Entomology 3rd edition - C.Gillott - Chapter 3 pps

3
E
xternal
S
tructur
e
1
. Intr
oduc
t
ion
T
he extreme variet
y
of external form seen in the Insecta is the most obvious manifestation
of this
g
roup’s adaptabilit
y
. To the taxonomist who thrives on morpholo
g
ical differences
,
t
his variet
y
is manna from Heaven; to the morpholo
g
ist who likes to refer ever
y
thin

g
back to
a
b
as
i
c type or groun
d
p
l
an,
i
t can
b
ean
i
g
h
tmare! Para
ll
e
li
ng t
hi
svar
i
ety
i
s, un
f

ortunate
l
y
,
a mass
i
ve term
i
no
l
ogy,event
h
e
b
as
i
cs o
f
w
hi
c
h
an e
l
ementary stu
d
ent may
fi
n
d diffi

cu
l
t
t
oa
b
sor
b
. Some conso
l
at
i
on ma
yb
e
d
er
i
ve
df
rom t
h
e
f
act t
h
at “
f
orm re
fl

ects
f
unct
i
on.”
I
n other words, seemin
g
l
y
minor differences in structure ma
y
reflect important difference
s
in functional ca
p
abilities. It is im
p
ossible to deal in a text of this kind with all of th
e
var
i
at
i
on
i
n
f
orm t
h

at ex
i
sts, an
d
on
l
yt
h
e
b
as
i
c structure o
f
an
i
nsect an
di
ts most
i
mportant
mo
difi
cat
i
ons
will b
e
d
escr

ib
e
d
.
2.
G
eneral Bod
y
Pla
n
Like other arthropods insects are se
g
mented animals whose bodies are covered wit
h
cuticle. Over most regions of the body the outer layer of the cuticle becomes hardened
(tanne
d
)an
df
orms t
h
e exocut
i
c
l
e (see C
h
apter 11, Sect
i
on 3.3). T

h
ese reg
i
ons are sepa-
rate
db
y areas (
j
o
i
nts)
i
nw
hi
c
h
t
h
e exocut
i
cu
l
ar
l
ayer
i
sm
i
ss
i

ng, an
d
t
h
e cut
i
c
l
et
h
ere
f
ore
remains membranous, flexible, and often folded. The presence of these cuticular membranes
facilitates movement between ad
j
acent hard parts (
s
clerites). The de
g
ree of movement at
a joint depends on the extent of the cuticular membrane. In the case of intersegmenta
l
mem
b
ranes t
h
ere
i
s comp

l
ete separat
i
on o
f
a
dj
acent sc
l
er
i
tes, an
d
t
h
ere
f
ore movement
i
s
u
nrestr
i
cte
d
. Usua
ll
y,
h
owever, espec

i
a
ll
y at appen
d
age
j
o
i
nts, movement
i
s restr
i
cte
dby
t
he development of one or two conti
g
uous points between ad
j
acent sclerites; that is, specific
articulations are
p
roduced.
A
m
onocondyli
c
j
oint has onl

y
one articulator
y
surface, and at
t
his
j
oint movement ma
y
be partiall
y
rotar
y
(e.
g
., the articulation of the antennae with th
e
h
ea
d
). In
d
icon
dyl
ic
j
o
i
nts (e.g., most
l

eg
j
o
i
nts) t
h
ere are two art
i
cu
l
at
i
ons, an
d
t
h
e
j
o
i
nt
operates
lik
ea
hi
nge. T
h
e art
i
cu

l
at
i
ons may
b
ee
i
t
h
e
r
i
ntrin
s
ic
,
w
h
ere t
h
e cont
i
guous po
i
nts
li
ew
i
t
hi

nt
h
e mem
b
rane (F
ig
ure 3.1A), or
e
xtrin
s
ic
,i
nw
hi
c
h
case t
h
e art
i
cu
l
at
i
n
g
sur
f
aces
lie outside the skeletal parts (Fi

g
ure 3.lB)
.
5
7
58
CHAPTER
3
F
I
GU
RE 3.1. Articulations. (A) Intrinsic (le
gj
oint); and (B) extrinsic (articulation of mandible with cranium).
[From R. E. Snodgrass
,
P
rinciples o
f
Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with per-
mi
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan

y
.]
In man
y
larval insects (as in annelids) the entire cuticle is thin and flexible, an
d
segments are separate
db
y
i
nvag
i
nat
i
ons o
f
t
h
e
i
ntegument
(
intersegmenta
lf
o
lds
)
t
o
whi

c
h
l
ong
i
tu
di
na
l
musc
l
es are attac
h
e
d
(F
i
gure 3.2A). An
i
ma
l
s possess
i
ng t
hi
s arrangement
(k
nown a
s
p

rimar
y
se
g
mentation
)h
ave
al
most un
li
m
i
te
df
ree
d
om o
fb
o
d
y movement. In
the ma
j
orit
y
of insects, however, there is heav
y
sclerotization of the cuticle to form a series
o
f dorsal and ventral

p
lates, the
t
erga
a
n
d
st
ern
a
,
respectivel
y
. As shown in Fi
g
ure 3.2B
,
F
IGURE 3.2. Types of body segmentation. (A) Primary; and (B) secondary. [From R. E. Snodgrass
,
P
rinciples o
f
I
nsect Morp
h
o
l
ogy
.

Cop
y
ri
g
ht 193
5
b
y
McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Compan
y
.
]
59
E
XTER
NAL
STRUCTURE
t
hese re
g
ions of sclerotization do not correspond precisel
y
with the primar
y
se
g
mental
pattern. The ter
g
al and sternal plates do not cover entirel

y
the posterior part of the primar
y
se
g
ment,
y
et the
y
extend anteriorl
y
sli
g
htl
y
be
y
ond the ori
g
inal interse
g
mental
g
roove
.
Th
us, t
h
e
b

o
d
y
i
s
diff
erent
i
ate
di
nto a ser
i
es o
f
secon
d
ary segments
(
s
c
l
eromat
a
)
se
p
arate
d
b
y mem

b
ranous areas
(
c
on
j
unctiva
e
)
t
h
at a
ll
ow t
h
e
b
o
d
y to rema
i
n
fl
ex
ibl
e. T
hi
s
i
s terme

d
secon
d
ar
y
se
g
mentation
.
Eac
h
secon
d
ar
y
se
g
ment conta
i
ns
f
our exos
k
e
l
eta
l
components,
a ter
g

um and a sternum separated b
y
lateral, primaril
y
membranous
,
p
leural areas
.
Each of
t
he primar
y
components ma
y
differentiate into several sclerites to which the
g
eneral term
s
ter
gi
tes
a
n
d
s
tern
i
te
s

are app
li
e
d
; sma
ll
sc
l
er
i
tes, genera
ll
y terme
d
pl
eurites, may a
l
so occu
r
i
nt
h
ep
l
eura
l
areas. T
h
epr
i

m
i
t
i
ve
i
ntersegmenta
lf
o
ld b
ecomes an
i
nterna
l
r
id
ge o
f
cut
i
c
l
e,
th
e anteco
s
ta, seen externa
ll
yasagroove,t
he

a
nteco
s
ta
ls
u
l
cu
s
.T
h
e narrow str
i
po
f
cut
i
c
le
anterior to the sulcus is th
e
a
crotergit
e
(
when dorsal
)
or
a
crosternit

e
(
when ventraJ
)
.Th
e
posterior part of both the ter
g
um and sternum is primitivel
y
a simple cuticular plate, but
t
his undergoes considerable modification in the thoracic region of the body. The pleurites
a
re usua
ll
y secon
d
ary sc
l
erot
i
zat
i
ons
b
ut
i
n
f

act may represent t
h
e
b
asa
l
segment o
f
t
he
a
ppen
d
ages. T
h
ep
l
eur
i
tes may
b
ecome great
l
yen
l
arge
d
an
df
use

d
w
i
t
h
t
h
e tergum an
d
sternum in the thoracic se
g
ments. In the abdomen the pleurites ma
y
fuse with the sternal
p
lates
.
The basic segmental structure is frequently obscured as a result of tagmosis. In insect
s
th
ree tagmata are
f
oun
d
:t
h
e
h
ea
d

,t
h
et
h
orax, an
d
t
h
ea
bd
omen. In t
h
e
h
ea
d
a
l
most a
ll
s
i
gns
o
f
t
h
eor
i
g

i
na
lb
oun
d
ar
i
es o
f
t
h
e segments
h
ave
di
sappeare
d
,t
h
oug
h
,
f
or most segments
,
t
he appenda
g
es remain. In the thorax the three se
g

ments can
g
enerall
y
be distin
g
uished,
a
lthou
g
h the
y
under
g
o profound modification associated with locomotion. The anterior
a
bdominal se
g
ments are usuall
y
little different from the t
y
pical secondar
y
se
g
ment described
ab
ove.Att
h

e poster
i
or en
d
o
f
t
h
ea
bd
omen a var
i
e
d
num
b
er o
f
segments may
b
emo
difi
e
d
,
re
d
uce
d
,or

l
ost, assoc
i
ate
d
w
i
t
h
t
h
e
d
eve
l
opment o
f
t
h
e externa
l
gen
i
ta
li
a.
Exam
i
nat
i

on o
f
t
h
e exos
k
e
l
eton revea
l
st
h
e presence o
f
a num
b
er o
fli
nes or
g
rooves
w
hose ori
g
in is varied. If the line marks the union of two ori
g
inall
y
separate sclerites, it is
kno

w
nas
a
su
t
ure
.I
fi
t
i
ndicates an inva
g
ination of the exoskeleton to form an internal rid
ge
o
f
cut
i
c
l
e
(
apo
d
em
e
)
,t
h
e

li
ne
i
s proper
l
y terme
da
s
u
l
cu
s
(Snodgrass, 1960). Pits may als
o
b
e seen on t
h
e exos
k
e
l
eton. T
h
ese p
i
ts mar
k
t
h
es

i
tes o
fi
nterna
l
,tu
b
ercu
l
ar
i
nvag
i
nat
i
ons
o
f
t
h
e
i
ntegument
(
apop
hy
se
s
)
. Secon

d
ary
di
scont
i
nuat
i
ons o
f
t
h
e exocut
i
cu
l
ar component
of the cuticle ma
y
occur, for example, the ecd
y
sial line alon
g
which the old cuticle splits
d
urin
g
moltin
g
, and these are
g

enerall
y
known as sutures.
Primitively each segment bore a pair of appendages. Traces of these can still be seen
on a
l
most a
ll
segments
f
oras
h
ort t
i
me
d
ur
i
ng em
b
ryon
i
c
d
eve
l
opment,
b
ut on many seg-
ments t

h
ey soon
di
sappear, an
d
typ
i
ca
li
nsects
l
ac
k
a
bd
om
i
na
l
appen
d
ages on a
ll
except
t
he posterior se
g
ments. Accordin
g
to Kukalov´a-Peck (1987), the

g
round plan of the insec
t
se
g
mental appenda
g
e included 11
p
odite
s
,
some of which carried inner or outer branches
(
endite
s
a
n
d
e
x
i
te
s
,
respectively) (Figure 3.21A). All of these podites can be identified in
some
f
oss
il i

nsects (Ku
k
a
l
ov´a-Pec
k
, 1992),
b
ut
i
nt
h
e great ma
j
or
i
ty o
f
extant
f
orms on
l
y
fi
ve or s
i
xpo
di
tes at most are o
b

v
i
ous, nota
bl
y
i
nt
h
e
l
egs
[
cox
a
,
troc
h
ante
r
,
f
emu
r
,
ti
b
ia
,
t
ar

s
u
s
(
an
d
p
retarsus,w
hi
c
h
some aut
h
ors
d
o not cons
id
er to
b
eapo
di
te)]. T
h
e appen
d
a
g
es
of the head and abdomen have become so hi
g

hl
y
modified that homolo
g
izin
g
their podite
s
ma
y
be extremel
y
difficult. Traces of exites can be seen as
g
ills in some aquatic
j
uvenile
i
nsects, an
d
t
h
een
di
tes rema
i
nast
h
e exsert
il

eves
i
c
l
es o
f
some apterygotes,
b
ut
i
nt
h
e
ma
j
or
i
ty o
fi
nsects t
h
ese
b
ranc
h
es
h
ave comp
l
ete

l
y
di
sappeare
d
.
60
CHAPTER
3
3
.Th
e
H
ead
Th
e
h
ea
d
,
b
e
i
n
g
t
h
e anter
i
or ta

g
ma,
b
ears t
h
ema
j
or sense or
g
ans an
d
t
h
e mout
h
parts
.
Considerable controvers
y
still surrounds the problem of se
g
mentation of the insect head,
e
speciall
y
concernin
g
the number and nature of se
g
ments anterior to the mouth.

*
At
v
ariou
s
times it has been argued that there are from three to seven segments in the insect head
,
t
h
oug
hi
t
i
snoww
id
e
l
y agree
d
t
h
at t
h
ere are s
i
x. It
i
s not
f
eas

ibl
eto
di
scuss
h
ere t
h
e man
y
t
h
eor
i
es concern
i
n
g
t
h
ese
g
menta
l
compos
i
t
i
on o
f
t

h
e
i
nsect
h
ea
d
,
b
ut t
h
ema
i
npo
i
nts o
f
c
ontention should be noted. These are: (1) whether arthropods possess an
acron
(
which is
non-se
g
mental and homolo
g
ous with the annelid prostomium); (2) whether
a
preantenna
l

s
egment occurs between the acron and the antennal segment and what appendages are
a
ssoc
i
ate
d
w
i
t
h
suc
h
a segment; an
d
(3) w
h
et
h
er t
he
a
ntennae
a
re segmenta
l
appen
d
ages o
r

merely outgrowths of the acron [see Rempel (197
5
), Bitsch (1994), Kukalov´a-Peck (1992)
,
a
nd Scholtz (1998) for reviews of the sub
j
ect]. The embr
y
olo
g
ical studies of Rempel and
C
hurch (1971) have demonstrated convincin
g
l
y
that an acron is present. However, it is never
s
een in fossil insects or other arthropods (Kukalov´a-Peck, 1992) because it moved dorsall
y
to merge
i
mpercept
ibl
y
i
nto t
h
ereg

i
on
b
etween t
h
e compoun
d
eyes (Ku
k
a
l
ov´a-Pec
k
, 1998).
Bot
h
em
b
ryo
l
ogy an
d
pa
l
eonto
l
ogy
h
ave con
fi

rme
d
t
h
at t
h
ere are t
h
ree preora
l
an
d
t
h
ree
p
ostoral se
g
ments The first preoral se
g
ment is preantennal; it is called the
p
rotocerebral
or
clypeolabral
s
e
g
ment. The se
g

ment itself has disappeared but its appenda
g
es remain as the
clypeolabrum
.
The second
p
reoral (
a
ntennal
/
deutocerebra
l
)
s
e
gment bears th
e
a
n
te
nn
ae
,
w
hi
c
h
are t
h

ere
f
ore true segmenta
l
appen
d
ages. T
h
et
hi
r
d
preora
l
(interca
l
ar
y
/tritocere
b
ra
l
)
s
egment appears
b
r
i
e
fl

y
d
ur
i
ng em
b
ryogenes
i
s, t
h
en
i
s
l
ost. Its appen
d
ages,
h
owever, rema
i
n
a
s part of the
h
ypopharynx (Kukalov´a-Peck, 1992). Head se
g
ments 4–
6
are postoral and
n

a
m
ed t
h
e
mandibula
r
,
m
axillary
,
an
d
labial
, respectivel
y
. Their appenda
g
es form the
mouth
p
arts from which their names are derived. In addition, the sternum of the mandibular
s
egment
b
ecomes part o
f
t
h
e

h
ypop
h
arynx
.
3.1.
G
eneral
S
tructure
P
rimitively the head is oriented so that the mouthparts lie ventrally (the hypognathou
s
con
di
t
i
on) (F
i
gure 3.3B). In some
i
nsects, espec
i
a
ll
yt
h
ose t
h
at pursue t

h
e
i
r prey or use t
h
e
i
r
mout
h
parts
i
n
b
urrow
i
ng, t
h
e
h
ea
di
s
p
ro
g
nat
h
ou
s

i
nw
hi
c
h
t
h
e mout
h
parts are
di
recte
d
a
nteriorl
y
(Fi
g
ure 3.4A). In man
y
Hemiptera the suctorial mouthparts are posteroventral i
n
p
osition (Fi
g
ure 3.4B), a condition described as opisthognathou
s
(
o
pisthorhynchous

).
The head takes the form of a heavily sclerotized capsule, and only the presence of th
e
a
ntennae an
d
mout
h
parts prov
id
es any externa
li
n
di
cat
i
on o
fi
ts segmenta
l
construct
i
on. In
most a
d
u
l
t
i
nsects an

dj
uven
il
e exopterygotes a pa
i
ro
f
compoun
d
e
y
e
s
i
ss
i
tuate
dd
orso
l
ater-
a
ll
y
on the cranium, with three
ocelli
b
etween them on the anterior face (Fi
g
ure 3.3A). Th

e
two
p
osterior ocelli are somewhat lateral in
p
osition; the third ocellus is anterior and median.
Th
e
a
n
te
nn
ae
v
ary in location from a point close to the mandibles to a more median positio
n
b
etween t
h
e compoun
d
eyes. On t
h
e poster
i
or sur
f
ace o
f
t

h
e
h
ea
d
capsu
l
e
i
s an aperture, t
h
e
occipita
l
forame
n
,w
hi
c
hl
ea
d
s
i
nto t
h
e nec
k
.O
f

t
h
e mout
h
parts, t
h
e
l
a
b
ru
m
h
angs
d
own
f
rom the ventral ed
g
eofth
e
c
lypeus
,
th
e
labium
l
ies below the occipital foramen, and th
e

*
P
erhaps the most interesting conclusion was drawn by Snodgrass (1960, p. 51) who stated “it would be too ba
d
if
t
h
e quest
i
on o
fh
ea
d
segmentat
i
on ever s
h
ou
ld b
e
fi
na
ll
y sett
l
e
d
;
i
t

h
as
b
een
f
or so
l
ong suc
hf
ert
il
e groun
d
f
or t
h
eor
i
z
i
n
g
t
h
at art
h
ropo
di
sts wou
ld

m
i
ss
i
tasa
fi
e
ld f
or menta
l
exerc
i
se”!
6
1
E
XTER
NAL
S
TRUCTURE
F
IGURE 3.3. Structure of the typical pterygotan head. (A) Anterior; (B) lateral; (C) posterior; and (D) ventral
(
appen
d
a
g
es remove
d
). [From R. E. Sno

dg
rass
.
P
rincip
l
es of Insect Morp
h
o
l
ogy .
C
op
y
ri
g
ht 193
5
b
y
McGraw-Hill,
Inc. Used with permission of McGraw-Hill Book Compan
y
.]
p
aired mandible
s
a
n
d

m
axillae
occup
y
ventrolateral positions (Fi
g
ure 3.3B). The mouth is
situated behind the base of the labrum. The true ventral surface of the head ca
p
sule is the
h
ypop
h
arynx (F
i
gure 3.3D), a mem
b
ranous
l
o
b
et
h
at
li
es
i
nt
h
e preora

l
cav
i
ty
f
orme
dby
th
e ventra
ll
y pro
j
ect
i
ng mout
h
parts
.
There are several
g
rooves and pits on the head (Fi
g
ure 3.3A–C), some of which, b
y
virtue of their constanc
y
of position within a particular insect
g
roup, constitute importan
t

t
axonomic features. The
g
rooves are almost all sulci. Th
e
p
ostoccipital sulcus
s
e
p
arates the
m
ax
ill
ary an
dl
a
bi
a
l
segments an
di
nterna
ll
y
f
orms a strong r
id
ge to w
hi

c
h
are attac
h
e
d
th
e musc
l
es use
di
nmov
i
ng t
h
e
h
ea
d
an
df
rom w
hi
c
h
t
h
e poster
i
or arms o

f
t
h
e tentorium
ar
i
se (see
f
o
ll
ow
i
n
g
para
g
rap
h
). T
h
epo
i
nts o
ff
ormat
i
on o
f
t
h

ese arms are seen externa
lly
as deep pits in the postoccipital
g
roove, the
p
osterior tentorial
p
it
s
.
Th
e
e
p
icranial sutur
e
62
CHAPTER
3
F
IGURE 3.4
.
(
A) Prognathous; and (B) opisthognathous types of head structure. [A, from R. E. Snodgrass,
Princip
l
es of Insect Morp
h
o

l
ogy
.
C
op
y
ri
g
ht 193
5
b
y
McGraw-Hill, Inc. Used with permission of McGraw-Hil
l
B
ook Compan
y
. B, after R. F. Chapman, 1971
,
T
he Insects:
S
tructure and Function
.
B
y
permission of Elsevie
r
North-Holland, Inc., and the author.
]

i
s a line of weakness occupying a median dorsal position on the head. It is also known a
s
the
ec
dy
sia
ll
in
e
,
f
or
i
t
i
sa
l
ong t
hi
s groove t
h
at t
h
e cut
i
c
l
esp
li

ts
d
ur
i
ng ec
d
ys
i
s. In man
y
i
nsects t
h
eep
i
cran
i
a
l
suture
i
s
i
nt
h
es
h
ape o
f
an

i
nverte
d
Yw
h
ose arms
di
verge a
b
ove t
h
e
m
edian ocellus and pass ventrall
y
over the anterior part of the head. Th
e
o
cci
p
ital sulcus
,
w
hich is commonl
y
found in orthopteroid insects, runs transversel
y
across the posterior
part of the cranium. Internall
y

it forms a rid
g
e that stren
g
thens this re
g
ion of the head. Th
e
s
u
bg
ena
l
su
l
cus
i
sa
l
atera
l
groove
i
nt
h
e cran
i
a
l
wa

ll
runn
i
ng s
li
g
h
t
l
ya
b
ove t
h
e mout
h
part
art
i
cu
l
at
i
ons. T
h
at part o
f
t
h
esu
b

gena
l
su
l
cus
l
y
i
ng
di
rect
l
ya
b
ove t
h
e man
dibl
e
i
s
k
nown
as t
h
e
pl
eurostoma
l
su

l
cu
s
;t
h
at part
lyi
n
gb
e
hi
n
di
st
h
e
hy
postoma
l
su
l
cu
s
,w
hi
c
hi
s usua
lly
c

ontinuous with the postoccipital suture. In man
y
insects the pleurostomal sulcus is contin
-
ued across the front of the cranium (above the labrum), where it is known as th
e
epistoma
l
(
f
rontoc
l
ypea
l
)
s
u
l
cu
s
.W
ithin this sulcus lie the
W
W
a
nterior tentoria
l
pit
s
,

w
hi
c
hi
n
di
cate t
he
i
nterna
l
or
i
g
i
no
f
t
h
e
a
nterior tentoria
l
arm
s
.T
he
antenna
l
a

n
d
o
cu
l
ar
s
u
l
c
i
i
n
di
cate
i
nterna
l
c
ut
i
cu
l
ar r
idg
es
b
rac
i
n

g
t
h
e antennae an
d
compoun
d
e
y
es, respect
i
ve
ly
.
A
s
u
b
ocu
l
ar
s
u
l
cu
s
runnin
g
dorsolaterall
y

beneath the compound e
y
e is often present.
63
E
XTER
NAL
S
TRUCTURE
F
I
GU
RE 3.5
.
Relationship of the tentorium to
g
rooves and pits on the head. Most of the head capsule has been
cut away. [From R. E. Snodgrass.
P
rinciples o
f
Insect Morphology
.
Copyright 1935 by McGraw-Hill, Inc. Use
d
w
i
t
h
perm

i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y
.]
The tentorium (Fi
g
ure 3.5) is an internal, cranial-supportin
g
structure whose mor
-
pholo
gy
varies considerabl
y
amon
g
different insect
g
roups. Like the
f
urc
a

o
f
t
h
et
h
o
r
ac
i
c
segments (Section 4.2), with which it is homologous, it is produced by invagination of the
exos
k
e
l
eton. Genera
ll
y,
i
t
i
s compose
d
o
f
t
h
e anter
i

or an
d
poster
i
or tentor
i
a
l
arms t
h
at ma
y
meet an
df
use w
i
t
hi
nt
h
e
h
ea
d
. Frequent
l
y, a
ddi
t
i

ona
l
supports
i
nt
h
e
f
orm o
fd
orsa
l
arms
are found. The latter are secondar
y
out
g
rowths of the anterior arms and not apodemes. Th
e
j
unction of the anterior and posterior arms is often enlar
g
ed and known as th
e
te
n
to
r
ial
b

ridg
e
or
c
orporotentor
i
u
m
.
In addition to bracing the cranium, the tentorium is also a site
f
or t
h
e
i
nsert
i
on o
f
musc
l
es contro
lli
ng movement o
f
t
h
e man
dibl
es, max

ill
ae,
l
a
bi
um, an
d
h
ypop
h
arynx.
The
g
rooves described above delimit particular areas of the cranium that are useful i
n
d
escriptive or taxonomic work. The ma
j
or areas are as follows. The
f
rontoclypeal area i
st
h
e
facial area of the head, between the antennae and the labrum. When the e
p
istomal sulcus is
p
resent, t
h

e area
b
ecomes
di
v
id
e
di
nto t
h
e
d
orsa
l
f
rons an
d
t
h
e ventra
l
c
l
ypeus. T
h
e
l
atter
is
o

f
ten
divid
e
di
nto a
p
ostc
ly
peus an
d
an
a
ntec
ly
peus
.
T
h
e
v
ertex
i
st
h
e
d
orsa
l
sur

f
ace o
f
t
h
e
h
ea
d
.It
i
s usua
lly d
e
li
m
i
te
d
anter
i
or
ly by
t
h
e arms o
f
t
h
eep

i
cran
i
a
l
suture an
d
poster
i
or
ly
by
the occipital sulcus. The vertex extends laterall
y
to mer
g
e with the
gena
,
whose anterior
,
posterior, and ventral limits are the subocular, occipital, and sub
g
enal sulci, respectivel
y.
Th
e
h
orses
h

oe-s
h
ape
d
area
l
y
i
ng
b
etween t
h
e occ
i
p
i
ta
l
su
l
cus an
d
postocc
i
p
i
ta
l
su
l

cus
i
s
genera
ll
y
di
v
id
e
di
nto t
h
e
d
orsa
l
o
cciput
,
w
hi
c
h
merges
l
atera
ll
yw
i

t
h
t
h
e post
g
ena
e
.T
he
p
ostocci
p
ut
i
st
h
e narrow poster
i
or r
i
mo
f
t
h
e cran
i
um surroun
di
n

g
t
h
e occ
i
p
i
ta
lf
oramen.
I
t bears a pair o
f
o
ccipital condyles
t
o which th
e
a
nterior cervical sclerite
s
are articulated
.
B
elow the
g
ena is a narrow area, th
e
s
ubgen

a
,on
w
hich the mandible and maxilla are
art
i
cu
l
ate
d
.T
h
e
l
a
bi
um
i
s usua
ll
y art
i
cu
l
ate
ddi
rect
l
yw
i

t
h
t
h
e nec
k
mem
b
rane (F
i
gure 3.3C),
b
ut
in
some
i
nsects a sc
l
erot
i
ze
d
reg
i
on separates t
h
etwo.T
hi
ssc
l

erot
i
ze
d
area
d
eve
l
ops
i
n one o
f
t
h
ree ways: as extens
i
ons o
f
t
h
esu
b
genae w
hi
c
hf
use
i
nt
h

em
idli
ne to
f
orm a
subgenal bridge
,ase
xtensions of the h
y
postomal areas to form
a
hypostomal bridge
,or
64
CHAPTER
3
(
in most pro
g
nathous heads) throu
g
h the extension ventrall
y
and anteriorl
y
of a ventra
l
c
ervical sclerite to form th
e

gul
a
.
At the same time the basal se
g
ment of the labium ma
y
also become elon
g
ated (Fi
g
ure 3.4A)
.
3
.2. Head
A
ppendage
s
3
.2.1.
A
nt
e
nn
ae
Apa
i
ro
f
antennae are

f
oun
d
on t
h
e
h
ea
d
o
f
t
h
e pter
yg
ote
i
nsects an
d
t
h
e apter
y
-
g
ote
g
roups with the exception of the Protura. However, in the larvae of man
y
hi

g
he
r
Hy
menoptera and Diptera the
y
are reduced to a sli
g
ht swellin
g
or disc.
In a typical antenna (Figure 3.6) there are three principal components: the basal
s
cap
e
b
yw
hi
c
h
t
h
e antenna
i
s attac
h
e
d
to t
h

e
h
ea
d
,t
h
e pe
d
ice
l
conta
i
n
i
ng Jo
h
nston’s organ
(
C
h
apter 12, Sect
i
on 3.1), an
d
t
h
e fla
g
e
ll

um,w
hi
c
hi
s usua
lly l
on
g
an
d
annu
l
ate
d
. Accor
d
-
i
n
g
to Kukalov´a-Peck (1992), the scape, pedicel, and fla
g
ellum are homolo
g
ous with th
e
s
ubcoxa, coxa, and remainin
g
se

g
ments, respectivel
y
, of the ancestral le
g
(Fi
g
ure 3.21A).
The annuli on the flagellum do not correspond with the ancestral leg joints; that is, the annuli
are constr
i
ct
i
ons, not sutures. T
h
e scape
i
s set
i
n a mem
b
ranous soc
k
et an
d
surroun
d
e
dby
t

h
e antenna
l
sc
l
er
i
te on w
hi
c
h
as
i
ng
l
e art
i
cu
l
at
i
on may occur. In t
h
ema
j
or
i
ty o
fi
nsects

m
ovement of the whole antenna is effected b
y
muscles inserted on the scape and attached
to the cranium or tentorium. However, in Collembola there is no Johnston’s or
g
an and each
antennal segment is moved by a muscle inserted in the previous segment.
A
l
t
h
oug
h
reta
i
n
i
ng t
h
e
b
as
i
c structure out
li
ne
d
a
b

ove, t
h
e antennae ta
k
eonaw
id
e
v
ar
i
ety o
ff
orms (F
i
gure 3.7) re
l
ate
d
to t
h
e
i
rvar
i
e
df
unct
i
ons. Genera
ll

y,
i
t
i
st
h
e
fl
age
ll
u
m
t
h
at
i
smo
difi
e
d
. For examp
l
e,
i
n some ma
l
e mot
h
san
db

eet
l
es t
h
e
fl
a
g
e
ll
um
i
sp
l
umose an
d
flabellate, respectivel
y
, providin
g
a lar
g
e surface area for the numerous chemosensilla that
g
ive these insects their remarkable sense of smell (see Chapter 12, Section 4). B
y
contrast,
t
h
ep

l
umose nature o
f
t
h
e antennae o
f
ma
l
e mosqu
i
toes ma
k
es t
h
em
hi
g
hl
y sens
i
t
i
ve to t
h
e
s
oun
d
s generate

db
yt
h
e
b
eat
i
ng o
f
t
h
e
f
ema
l
e’s w
i
ngs (C
h
apter 12, Sect
i
on 3.1). Ot
h
e
r
f
unct
i
ons o
f

antennae
i
nc
l
u
d
e touc
hi
n
g
, temperature an
dh
um
idi
t
y
percept
i
on,
g
rasp
i
n
g
pre
y
, and holdin
g
on to the female durin
g

matin
g
(Schneider, 1964; Zacharuk, 1985). Fo
r
taxonomists, this variet
y
of form ma
y
be an important dia
g
nostic feature.
3
.
2
.
2
. Mouthparts
T
he mouthparts consist of the labrum, a pair of mandibles, a pair of maxillae, the
l
abium, and the h
y
pophar
y
nx. In Collembola, Protura, and Diplura the mouthparts ar
e
FI
G
URE 3.6
.

Structure o
f
an antenna. [From R. E.
S
nod
g
rass
,
Principles o
f
Insect Morphology
.
Cop
y
ri
g
h
t
1
935 by McGraw-Hill, Inc. Used with permission o
f
McGraw-H
ill
Boo
k
Compan
y
.]
65
E

XTER
NAL
S
TRUCTURE
F
I
GU
RE 3.7. T
y
pes of antennae. [After A. D. Imms, 1957
,
A General Textbook o
f
Entomolog
y
, 9th ed.
(
revised
b
y O. W. Richards and R. G. Davies), Methuen and Co.]
enclosed within a cavit
y
formed b
y
the ventrolateral extension of the
g
enae, which fuse in
t
he midline (the entognathou
s

condition). In Microcor
y
phia, Z
yg
entoma, and Pter
yg
ota th
e
mout
h
parts pro
j
ect
f
ree
l
y
f
rom t
h
e
h
ea
d
capsu
l
e, a con
di
t
i

on
d
escr
ib
e
d
a
s
ecto
g
nat
h
ou
s
.
Th
e
f
orm o
f
t
h
e mout
h
parts
i
s extreme
l
yvar
i

e
d
(see
b
e
l
ow), an
di
t
i
s appropr
i
ate to
d
escr
ib
e
fi
rst t
h
e
i
r structure
i
nt
h
e more pr
i
m
i

t
i
ve c
h
ew
i
n
g
con
di
t
i
on
.
Typical Chewing Mouthparts
.
Inat
y
pical chewin
g
insect the labrum (Fi
g
ure 3.3A
)
is a broadly flattened plate hinged to the clypeus. Its ventral (inner) surface is usually
mem
b
ranous an
df
orms t

h
e
l
o
b
e-
lik
eep
i
p
h
arynx, w
hi
c
hb
ears mec
h
ano- an
d
c
h
emosens
ill
a.
T
h
e man
dibl
e(F
i

gure 3.8A)
i
sa
h
eav
il
ysc
l
erot
i
ze
d
, rat
h
er compact structure
h
av
i
ng
a
l
most a
l
wa
y
sa
di
con
dyli
c art

i
cu
l
at
i
on w
i
t
h
t
h
esu
bg
ena. Its
f
unct
i
ona
l
area var
i
es accor
d-
in
g
to the diet of the insect. In herbivorous forms there are both cuttin
g
ed
g
es and

g
rindin
g
surfaces on the mandible. The cuttin
g
ed
g
es are t
y
picall
y
stren
g
thened b
y
the addition o
f
zi
nc, manganese or, rare
l
y,
i
ron,
i
n amounts up to a
b
out 4% o
f
t
h

e
d
ry we
i
g
h
t. In carn
i
vorou
s
spec
i
es t
h
e man
dibl
e possesses s
h
arp
l
ypo
i
nte
d
“teet
h
”
f
or cutt
i

ng an
d
tear
i
ng. In M
i
croco-
r
y
p
hi
at
h
e man
dibl
e
h
asas
i
n
gl
e art
i
cu
l
at
i
on w
i
t

h
t
h
e cran
i
um an
d
, as a resu
l
t, muc
hg
reater
freedom of movement
.
Of all of the mouthparts the maxilla (Fi
g
ure 3.8B) retains most closel
y
the structur
e
o
f
t
h
epr
i
m
i
t
i

ve
i
nsectan
li
m
b
.T
h
e
b
asa
l
segment
i
s
di
v
id
e
db
y a transverse
li
ne o
ffl
exure
i
nto two su
b
segments, a prox
i

ma
l
c
ar
do
a
n
d
a
di
sta
l
s
tipe
s
.
T
h
e car
d
o carr
i
es t
h
es
i
ng
le
con
d

y
l
ew
i
t
h
w
hi
c
h
t
h
e max
ill
a art
i
cu
l
ates w
i
t
h
t
h
e
h
ea
d
. Bot
h

t
h
e car
d
oan
d
st
i
pes are
,
h
owever, attached on their entire inner surface to the membranous head pleuron. The stipes
66
CHAPTER
3
F
IGURE 3.8
.
S
tructure o
f
(A) man
dibl
e, (B) max
ill
a, an
d
(C)
l
a

bi
um o
f
a typ
i
ca
l
c
h
ew
i
ng
i
nsect. [Fro
m
R
.E.Sno
dg
rass
,
Princip
l
es of Insect Morp
h
o
l
ogy . Cop
y
ri
g

ht 193
5
b
y
McGraw-Hill, Inc. Used with permissio
n
o
f McGraw-Hill Book Company.
]
bea
r
sa
n inn
er
laci
n
ia
a
n
d oute
r gale
a
,
and
a
m
axillary pal
p
.
This basic structure is found i

n
b
ot
h
apterygotes an
d
t
h
ema
j
or
i
ty o
f
c
h
ew
i
ng pterygotes, a
l
t
h
oug
hi
n some
f
orms re
d
uct
i

o
n
or loss of the lacinia, galea, or palp occurs. In Kukalov´
a-Peck’s (1991) view the cardo
´
an
d
st
i
pes correspon
d
to t
h
esu
b
coxa an
d
coxa
+
troc
h
anter, respect
i
ve
ly
,o
f
t
h
e ancestra

l
appenda
g
e; the lacinia and the
g
alea to the coxal and trochanteral endites, respectivel
y
;an
d
the palp to the remainin
g
se
g
ments. The laciniae assist in holdin
g
and masticatin
g
the food,
whil
et
h
ega
l
eae an
d
pa
l
ps are equ
i
ppe

d
w
i
t
h
avar
i
ety o
f
mec
h
ano- an
d
c
h
emosens
ill
a
.
Th
e
l
a
bi
um (F
i
gure 3.8C)
i
s
f

orme
db
yt
h
eme
di
a
lf
us
i
on o
f
t
h
epr
i
m
i
t
i
ve appen
d
age
s
of
t
h
e postmax
ill
ar

y
se
g
ment, to
g
et
h
er w
i
t
h
,
i
n
i
ts
b
asa
l
re
gi
on, a sma
ll
part o
f
t
h
e sternum
o
f that se

g
ment. The labium is divided into two primar
y
re
g
ions, a proximal
p
os
t
men
t
u
m
c
orrespondin
g
to the maxillar
y
cardines plus the sternal component, and a distal
p
remen-
tum
h
omo
l
ogous w
i
t
h
t

h
e max
ill
ary st
i
p
i
tes. T
h
e postmentum
i
s usua
ll
ysu
bdi
v
id
e
di
nto
s
u
b
mentum
a
n
d
mentum reg
i
ons. T

h
e prementum
b
ears a pa
i
ro
fi
nner
gl
ossae an
d
apa
i
ro
f
o
u
t
e
r
para
gl
ossa
e
,
h
omo
l
o
g

ous w
i
t
h
t
h
e max
ill
ar
yl
ac
i
n
i
ae an
dg
a
l
eae, respect
i
ve
ly
,an
da
p
air of labial
p
al
p
s. When the

g
lossae and para
g
lossae are fused the
y
form a sin
g
le structur
e
te
rm
ed t
h
e
ligul
a
.
Ar
i
s
i
ng as a me
di
an, ma
i
n
l
y mem
b
ranous,

l
o
b
e
f
rom t
h
e
fl
oor o
f
t
h
e
h
ea
d
capsu
l
ean
d
pro
j
ect
i
ng ventra
ll
y
i
nto t

h
e preora
l
cav
i
ty
i
st
h
e
h
ypop
h
arynx (F
i
gures 3.3D an
d
3.9). I
t
i
s
f
requent
l
y
f
use
d
to t
h

e
l
a
bi
um. In a
f
ew
i
nsects (
b
r
i
st
l
eta
il
san
d
may
fl
y
l
arvae) a pa
i
r
o
f lobes
,
the superlinguae
,

which arise embr
y
onicall
y
in the mandibular se
g
ment, becom
e
associated with the h
y
pophar
y
nx. The h
y
pophar
y
nx divides the preoral cavit
y
into anterio
r
and
p
osterior s
p
aces, the u
pp
er
p
arts of which are the
ciba

r
ium
(
leading to the mouth) and
s
a
l
i
v
arium (
i
nto w
hi
c
h
t
h
esa
li
vary
d
uct opens), respect
i
ve
l
y
.
Mouth
p
art Modifications.

Th
et
y
p
i
ca
l
c
h
ew
i
n
g
mout
h
parts
d
escr
ib
e
d
a
b
ove can
b
e
f
ound with minor modifications in Odonata, Pleco
p
tera, the ortho

p
teroids and blattoids
,
67
E
XTER
NAL
S
TRUCTURE
F
I
GU
RE 3.9.
S
implified sectional diagram through the insect head showing the general arrangement of the
p
arts. [From R. E. Sno
d
grass,
P
rincip
l
es of Insect Morp
h
o
l
ogy . Copyright 1935 by McGraw-Hill, Inc. Used wit
h
p
erm

i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y
.
]
N
europtera and Coleoptera (with the exceptions mentioned below), Mecoptera, primitive
H
y
menoptera, and larval Ephemeroptera, Trichoptera, and Lepidoptera. However, the basi
c
arrangement may undergo great modification associated with specialized feeding habits
(espec
i
a
ll
yt
h
e upta
k
eo
fli

qu
id f
oo
d
)orot
h
er, nontrop
hi
c
f
unct
i
ons. Suctor
i
a
l
mout
h
parts
are
f
oun
di
n mem
b
ers o
f
t
h
e

h
em
i
ptero
id
or
d
ers, an
d
a
d
u
l
tS
i
p
h
onaptera, D
i
ptera,
hi
g
h
er
H
y
menoptera, and Lepidoptera. The mouthparts are reduced or absent in non-feedin
g
or
endo

p
arasitic forms
.
Examination of the structure of the mouth
p
arts
p
rovides information on an insect’
s
di
et an
df
ee
di
ng
h
a
bi
ts, an
di
sa
l
so o
f
ass
i
stance
i
n taxonom
i

c stu
di
es. Some o
f
t
h
e more
i
mportant mo
difi
cat
i
ons
f
or t
h
e upta
k
eo
fli
qu
id f
oo
d
are
d
escr
ib
e
db

e
l
ow.Itw
ill b
e note
d
th
at a
ll
suc
ki
n
gi
nsects
h
ave two
f
eatures
i
n common. Some components o
f
t
h
e
i
r mout
h
part
s
are modified into tubular structures, and a suckin

g
pump is developed for drawin
g
the food
into the mouth
.
C
oleoptera and Neuroptera
.
In certa
i
n spec
i
es o
f
Co
l
eoptera an
d
Neuroptera t
he
mout
h
parts o
f
t
h
e
l
arvae are mo

difi
e
df
or grasp
i
ng,
i
n
j
ect
i
ng, an
d
suc
ki
ng. In t
h
e
b
eet
l
e
Dystiscu
s
, for example, the laterall
y
placed mandibles are lon
g
, curved structures with a
g

roove havin
g
confluent ed
g
es on their inner surface (Fi
g
ure 3.10). The labrum and labium
are closely apposed so that the cibarium is cut off from the exterior. When prey is grasped,
di
gest
i
ve
fl
u
id
s
f
rom t
h
em
id
gut are
f
orce
d
a
l
ong t
h
e man

dib
u
l
ar grooves an
di
nto t
h
e
b
o
d
y
.
A
f
ter externa
ldi
gest
i
on,
li
que
fi
e
d
mater
i
a
li
s suc

k
e
db
ac
ki
nto t
h
ec
ib
ar
i
um. In D
y
tiscus
th
e suctor
i
a
l
pump
i
s constructe
df
rom t
h
ec
ib
ar
i
um, t

h
ep
h
ar
y
nx, an
d
t
h
e
i
r
dil
ator musc
l
es
(see Fi
g
ure 3.9)
.
Hymenoptera. In adult Hymenoptera a range of specialization of mouthparts can
b
e seen. In pr
i
m
i
t
i
ve
f

orms, suc
h
as saw
fli
es, t
h
e man
dibl
e
i
s a typ
i
ca
lbi
t
i
ng structure, an
d
th
e max
ill
ae an
dl
a
bi
um, t
h
oug
h
un

i
te
d
,st
ill
ex
hibi
tt
h
e
i
r component parts. In t
h
ea
d
vance
d
forms, such as bees, the mandibles become flattened and are used for
g
raspin
g
and moldin
g
68
CHAPTER
3
F
I
GU
RE 3.10

.
L
e
f
t
m
a
n
d
i
b
l
eo
f D
y
t
i
scu
s
larva, seen dorsall
y
, showin
g
t
he canal on its inner side. [From R. E. Snodgrass,
P
rinciples of Insec
t
Morp
h

o
l
ogy.
C
op
y
ri
g
ht 193
5
b
y
McGraw-Hill. Inc. Used with permission
of McGraw-Hill Book Compan
y
.
]
m
ater
i
a
l
s rat
h
er t
h
an
bi
t
i

n
g
an
d
cutt
i
n
g
.T
h
e max
ill
o
l
a
bi
a
l
comp
l
ex
i
se
l
on
g
ate an
d
t
he

g
lossae form a lon
g
flexible “ton
g
ue,” a suckin
g
tube capable of retraction and protractio
n
(
Fi
g
ure 3.11). The laciniae are lost and the maxillar
y
palps reduced, but the
g
aleae are muc
h
e
n
l
arge
d
,
fl
attene
d
structures, w
hi
c

hi
ns
h
ort-tongue
db
ees are use
d
to cut
h
o
l
es
i
nt
h
e
fl
ower
c
oro
ll
atoga
i
n access to t
h
e nectary. W
h
en t
h
e

f
oo
di
s eas
il
y access
ibl
e, t
h
eg
l
ossae,
l
a
bi
a
l
pa
l
ps, an
d
t
h
e
g
a
l
eae
f
orm a compos

i
te tu
b
eupw
hi
c
h
t
h
e
li
qu
id i
s
d
rawn. W
h
en t
h
e
f
oo
d
i
s confined in a narrow cavit
y
such as a nectar
y
, onl
y

the
g
lossae are used to obtain it. Th
e
suckin
g
mechanism of the H
y
menoptera includes the phar
y
nx, buccal cavit
y
, and cibarium,
and their dilator muscles.
Le
p
ido
p
tera. Funct
i
ona
lbi
t
i
ng mout
h
parts are reta
i
ne
di

nt
h
ea
d
u
l
ts o
f
on
l
y one
f
am
ily
o
f
Lep
id
optera, t
h
eM
i
cropter
igid
ae. In a
ll
ot
h
er
g

roups t
h
e mout
h
parts (F
ig
ure 3.12
)
are considerabl
y
modified in con
j
unction with the diet of nectar. The mandibles are usuall
y
l
ost, the labrum is reduced to a narrow transverse sclerite, and the labium is a small fla
p
FI
GU
RE 3.11.
M
outhparts of the hone
y
bee. [After R
.
E. Snodgrass. 1925, Anatomy and Physiology o
f
the Hone
y
b

ee, McGraw-H
ill
Boo
k
Compan
y
.]
69
E
XTER
NAL
STRUCTURE
F
I
GU
RE 3.12.
H
ea
d
an
d
mout
hp
arts o
f
Le
pid
o
p
tera. (A) Genera

l
v
i
ew o
f
t
h
e
h
ea
d
an
d
(B) cross-sect
i
on o
f
t
h
e
p
roboscis. [From R. E. Snodgrass, Principles o
f
Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Use
d
w
i
t
h
perm

i
ss
i
on o
f
McGraw-H
ill
Boo
k
Company.]
(thou
g
h its palps remain quite lar
g
e). The lon
g
, suctorial proboscis is formed from the
interlockin
gg
aleae, whose outer walls comprise a succession of narrow sclerotized arc
s
a
l
ternat
i
ng w
i
t
h
t

hi
n mem
b
ranous areas: presuma
bl
yt
hi
s arrangement
f
ac
ili
tates co
ili
ng.
E
xtens
i
on o
f
t
h
e pro
b
osc
i
s
i
s
b
roug

h
ta
b
out
b
ya
l
oca
li
ncrease
i
n
bl
oo
d
pressure. T
h
e suc
ki
n
g
pump o
f
Lep
id
optera compr
i
ses t
h
e same e

l
ements as t
h
at o
f
H
y
menoptera. In Lep
id
opter
a
t
hat do not feed as adults all mouthparts are
g
reatl
y
reduced and the pump is absent
.
Di
ptera.
I
n both larval and adult Di
p
tera the form and function of the mouth
p
art
s
h
ave
di

verge
d
cons
id
era
bl
y
f
rom t
h
e typ
i
ca
l
c
h
ew
i
ng con
di
t
i
on. In
d
ee
d
,
i
n extreme cases
[seen

i
n some o
f
t
h
e
l
arvae (maggots) o
f
Muscomorp
h
a]
i
t appears t
h
at not on
l
yanew
f
ee
di
n
g
mec
h
an
i
sm
b
ut an ent

i
re
ly
new
f
unct
i
ona
lh
ea
d
an
d
mout
hh
ave evo
l
ve
d
,t
h
e tru
e
mouthparts of the adult fl
y
bein
g
suppressed durin
g
the larval period. This remarkabl

e
modification of the head and its appenda
g
es is, of course, the result of the insect livin
g
ent
i
re
l
yw
i
t
hi
n
i
ts
f
oo
d
.
La
r
v
a.
In
l
arvae o
f
many ort
h

orr
h
ap
h
ous
fli
es t
h
e
h
ea
di
s retracte
di
nto t
h
et
h
orax
and enclosed within a sheath formed from the neck membrane. The mandibles and maxilla
e
possess the t
y
pical bitin
g
structure (thou
g
h the palps are small or absent). The labrum i
s
large and overhanging. The labium is rudimentary and often confused with the hypostom

a
,
a toot
h
e
d
,tr
i
angu
l
ar sc
l
er
i
te on t
h
e nec
k
mem
b
rane (F
i
gure 3.13A–C).
I
n maggots t
h
e true
h
ea
di

s comp
l
ete
l
y
i
nvag
i
nate
di
nto t
h
et
h
orax, an
d
t
h
e con
i
ca
l
“head” is
,
in fact
,
a sclerotized fold of the neck. The functional “mouth” is the inner end of
t
he preoral cavit
y

, the
at
r
iu
m
,
from which a
p
air of sclerotized hooks
p
rotrude. The cibariu
m
is transformed into a massive suckin
g
pump, and the true mouth is the posterior exit from
th
e pump
l
umen (F
i
gure 3.13D)
.
A
dult. No a
d
u
l
tD
i
ptera

h
ave t
y
p
i
ca
lbi
t
i
n
g
mout
h
parts, a
l
t
h
ou
gh
,o
f
course, man
y
b
lood feeders are said to “bite” when the
y
pierce the skin. The mouthparts can be divided
functionall
y
into those that onl

y
suck and those that first pierce and then suck. In the latter
th
ep
i
erc
i
ng structure may
b
et
h
e man
dibl
es, t
h
e
l
a
bi
um, or t
h
e
h
ypop
h
arynx
.
I
nD
i

ptera t
h
at mere
l
y suc
k
or “sponge” up t
h
e
i
r
f
oo
d
(e.g., t
h
e
h
ouse
fl
yan
dbl
ow
fl
y
)
th
e man
dibl
es

h
ave
di
sappeare
d
an
d
t
h
ee
l
ongate
f
ee
di
ng tu
b
e, t
he
p
ro
b
oscis
,i
s
a
compos
i
t
e

structure that includes the labrum, h
y
pophar
y
nx, and labium (Fi
g
ure 3.14). The probosci
s
7
0
CHAPTER
3
F
I
G
URE 3.13
.
Hea
d
an
d
mout
h
parts o
fl
arva
l
D
i
ptera. (A) D

i
a
g
rammat
i
c sect
i
on t
h
rou
gh
t
h
e retracte
dh
ea
d
o
f
T
i
p
ula; (B) ri
g
ht mandible of Ti
p
ul
a
;
(

C
)
left maxilla of
T
i
p
ula
;
and (D) dia
g
rammatic section throu
g
h the anterior
e
n
d
o
f
a maggot. [From R. E. Sno
d
grass,
P
rincip
l
es of Insect Morp
h
o
l
ogy . Copyright 1935 by McGraw-Hill, Inc.
Use

d
w
i
t
h
perm
i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y
.]
i
s divisible into a basa
l
r
os
t
rum bearin
g
the maxillar
y
palps, a median flexible haustellum
,

and two a
p
ical
labella
.
The latter are broad spon
g
in
g
pads, equipped with
p
seudotrachea
e
along which food passes to the oral aperture. The latter is not the true mouth, which lies at
t
h
e upper en
d
o
f
t
h
e
f
oo
d
cana
l
.As
i

not
h
er D
i
ptera, t
h
e suc
ki
ng apparatus
i
s
f
orme
df
ro
m
t
h
ec
ib
ar
i
um an
di
ts
dil
ator musc
l
es t
h

at are
i
nserte
d
on t
h
ec
l
ypeus.
M
an
y
D
i
ptera
f
ee
d
on
bl
oo
d
. Some o
f
t
h
ese (e.
g
., t
h

e tsetse
fly
, sta
bl
e
fly
,an
dh
orn
fly
),
l
ike their non-piercin
g
relatives, have a composite proboscis. However, the haustellum is
e
lon
g
ate and ri
g
id, and the distal labellar lobes are small but bear rows o
f
prestomal teet
h
o
nt
h
e
i
r

i
nner
w
a
ll
s. T
h
e
l
a
b
rum an
dl
a
bi
um
i
nter
l
oc
k
to
f
orm t
h
e
f
oo
d
cana

lwi
t
hi
n
whi
c
h
l
ies the hypopharynx enclosing the salivary duct (Figure 3.1
5
)
.
O
t
h
er
bl
oo
d
-
f
ee
di
n
gfli
es (e.
g
.,
h
orse

fli
es,
d
eer
fli
es,
bl
ac
kfli
es, an
d
mosqu
i
toes) use
the mandibles for piercin
g
the host’s skin. The mouthparts of the horse fl
y
T
abanus ma
y
b
e
71
E
XTER
NAL
S
TRUCTURE
F

I
GU
RE 3.14
.
H
ead and mouthparts of the house fly. (A) Lateral view of the head with the proboscis extended
;
an
d
(B) antero
di
sta
l
v
i
ew o
f
t
h
e pro
b
osc
i
s. [From R. E. Sno
d
grass, Princip
l
es of Insect Morp
h
o

l
ogy
.
C
opyr
i
g
h
t
193
5
b
y
McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Compan
y
.]
F
I
GU
RE 3.15.
M
outhparts of the tsetse fly. (A) Cross-section; and (B) lateral view of the proboscis. [From
R
.E.Sno
d
grass, Princip
l
es of Insect Morp
h
o

l
ogy
.
C
opyright 1935 by McGraw-Hill, Inc. Used with permission
o
f
McGraw-H
ill
Boo
k
Compan
y
.
]
t
aken as an example (Fi
g
ure 3.1
6
). The labrum is da
gg
er-shaped but flexible and blunt at th
e
t
ip. On its inner side is a
g
roove closed posteriorl
y
b

y
the mandibles to form the food canal.
T
he mandibles are long and sharply pointed. The maxillae retain most of the components o
f
th
e typ
i
ca
lbi
t
i
ng
f
orm (except t
h
e
l
ac
i
n
i
ae)
b
ut t
h
ega
l
eae are
l

ong
bl
a
d
e
lik
e structures. T
he
h
ypop
h
arynx
i
s a sty
l
et
lik
e structure an
d
conta
i
ns t
h
esa
li
vary
d
uct. T
h
e

l
a
bi
um
i
sa
l
arge
,
t
hick appenda
g
e with a deep anterior
g
roove into which the other mouthparts normall
y
fit
.
Distall
y
it bears two lar
g
e labellar lobes. Blood flows alon
g
the pseudotracheae to the tip
of the food canal
.
Hemi
p
tera.

Th
ema
j
or contr
ib
utor to t
h
e
h
em
i
pteran pro
b
osc
i
s(F
i
gure 3.17)
i
st
he
l
a
bi
um, a
fl
ex
ibl
ese
g

mente
d
structure w
i
t
h
a
d
eep
g
roove on
i
ts anter
i
or sur
f
ace. W
i
t
hin
t
his
g
roove are found the piercin
g
or
g
ans, th
e
mandibular

a
nd maxillary bristles. The two
7
2
CHAPTER
3
F
I
GU
RE 3.16
.
H
ead and mouthparts of the horse fly.(A)Anteriorview of the head; and (B–E) lateral views of the
separate
d
mout
h
parts. [From R. E. Sno
d
grass, Princip
l
es of Insect Morp
h
o
l
ogy
.
C
opyright 1935 by McGraw-Hill
,

I
nc. Use
d
w
i
t
h
perm
i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y
.
]
F
I
GU
RE 3.17. Head and mouth
p
arts of Hemi
p
tera. (A) Head with the mouth
p

arts se
p
arated; and (B) cross
-
section of the proboscis. [From R. E. Snodgrass,
P
rinciples o
f
Insect Morphology
.
Copyright 1935 by McGraw-Hill,
I
nc. Use
d
w
i
t
h
perm
i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y

.
]
m
axillary bristles are interlocked within the labial groove and form the food and salivar
y
c
ana
l
s. Because o
f
t
h
e great en
l
argement o
f
t
h
ec
l
ypea
l
reg
i
on o
f
t
h
e
h

ea
d
assoc
i
ate
d
w
i
t
h
t
h
eop
i
st
h
ognat
h
ous con
di
t
i
on, t
h
ec
ib
ar
i
a
l

suc
ki
ng pump
i
s ent
i
re
l
yw
i
t
hi
nt
h
e
h
ea
d
.
4
. The
N
eck and Thorax
T
he thorax is the locomotor
y
center of the insect. T
y
picall
y

each of its three se
g
ments
(
pro-, meso-, and metathorax) bears a pair of le
g
s, and in the adult sta
g
e of the Pter
yg
ota th
e
73
E
XTER
NAL
S
TRUCTURE
meso- and metathoracic se
g
ments each have a pair of win
g
s. Between the head and thora
x
is the membranous neck
(
cerv
i
x
).

4.1. The Nec
k
S
tu
dy
o
fi
ts em
b
r
y
on
i
c
d
eve
l
opment s
h
ows t
h
at t
h
e nec
k
conta
i
ns
b
ot

hl
a
bi
a
l
an
d
prothoracic components and therefore the primar
y
interse
g
mental line must be within the
neck membrane. The muscles that control head movement arise on the postoccipital rid
g
e
an
d
are attac
h
e
d
to t
h
e antecosta o
f
t
h
e prot
h
orac

i
c segment. T
h
us, t
h
ey must
i
nc
l
u
d
et
he
fib
ers o
f
two segments. T
hi
smo
difi
cat
i
on o
f
t
h
e
b
as
i

c segmenta
l
structure was apparent
l
y
necessar
y
to prov
id
esu
ffi
c
i
ent
f
ree
d
om o
fh
ea
d
movement.
U
suall
y
supportin
g
the head and articulatin
g
it with the prothorax are the cervical

sclerites, a pair of which occur on each side of the neck (Fi
g
ure 3.3B). Either one o
r
b
oth sclerites may be absent. When only one occurs, it is often fused with the prothorax
.
Occas
i
ona
ll
y, a
ddi
t
i
ona
ld
orsa
l
an
d
ventra
l
sc
l
er
i
tes are
f
oun

d
.
4.2.
S
tructure of the Thora
x
I
n the evolution of the typical insectan body plan there have been two phases associated
wi
t
h
t
h
e
d
eve
l
opment o
f
t
h
et
h
orax as t
h
e
l
ocomotory center;
i
nt

h
e
fi
rst t
h
ewa
lki
ng
l
eg
s
b
ecame restr
i
cte
d
to t
h
et
h
ree t
h
orac
i
c segments, an
di
nt
h
e secon
d

art
i
cu
l
ate
d
w
i
ngs were
formed on the meso- and metathoracic ter
g
a. Accompan
y
in
g
each of these development
s
w
ere ma
j
or chan
g
es in the basic structure of the secondar
y
se
g
ments of the thoracic re
g
ion
.

T
hese chan
g
es were primaril
y
to stren
g
then the re
g
ion for increased muscular power.
I
nt
h
e apterygotes an
d
many
j
uven
il
e pterygotes t
h
et
h
orac
i
c terga are
li
tt
l
e

diff
eren
t
f
rom t
h
ose o
f
t
h
e typ
i
ca
l
secon
d
ary segment
d
escr
ib
e
di
n Sect
i
on 2. In t
h
ea
d
u
l

tt
h
e terga o
f
th
ew
i
n
g
-
b
ear
i
n
g
se
g
ments are en
l
ar
g
e
d
an
d
muc
h
mo
difi
e

d
(F
ig
ure 3.18). A
l
t
h
ou
gh i
tma
y
remain a sin
g
le plate, the ter
g
um (or n
otum
,a
s
i
t
is
c
alled in the thoracic se
g
ments) is usuall
y
d
ivided into the anterior win
g

-bearin
g
ali
n
otum
,
and the
p
osterior
p
os
t
no
t
u
m
.
These ar
e
fi
rm
l
y supporte
d
on t
h
ep
l
eura
l

sc
l
erot
i
zat
i
on
b
y means o
f
t
h
e
p
rea
l
ar
a
n
d
p
osta
l
ar arms
,
respect
i
ve
l
y. T

h
e antecostae o
f
t
h
epr
i
m
i
t
i
ve segments
b
ecome great
l
yen
l
arge
df
orm
i
ng
ph
ra
g
mata
,to
whi
c
h

t
h
e
l
arge
d
orsa
ll
ong
i
tu
di
na
l
musc
l
es are attac
h
e
d
.Asw
i
ng movemen
t
is in part brou
g
ht about b
y
flexure of the ter
g

a (see Chapter 14, Section 3.3.3), which i
s
itself caused b
y
contraction and relaxation of the dorsal lon
g
itudinal muscles, it is clear that
t
he connection bet
w
een the mesono
t
um
a
n
d
m
e
t
ano
t
u
m
and bet
w
een the metanotum and
fi
rst a
bd
om

i
na
l
tergum must
b
er
i
g
id
.T
h
e
i
ntersegmenta
l
mem
b
ranes are t
h
ere
f
ore re
d
uce
d
or a
b
sent. A
ddi
t

i
ona
l
support
i
ng r
id
ges are
d
eve
l
ope
d
on t
h
e meso- an
d
metanota, t
h
e most
common of which are the V-shaped
s
cutoscutellar ridg
e
a
nd th
e
t
ransverse (
p

rescutal
)
r
idg
e
(
Fi
g
ure 3.18A). The lateral mar
g
ins of the alinotum are constructed for articulation of
t
he wing. They possess bot
h
a
n
te
r
io
r
a
n
d
p
osterior notal processes
,
to
w
hich th
e

fi
rs
t
a
n
d
t
h
ir
d
axi
ll
ar
y
sc
l
erites
,
respect
i
ve
l
y, are attac
h
e
d
. Furt
h
er
d

eta
il
so
f
t
h
ew
i
ng art
i
cu
l
at
i
on
are g
i
ven
i
n Sect
i
on 4.3.2
.
The ori
g
inall
y
membranous pleura have been stren
g
thened to var

y
in
g
de
g
rees b
y
scle-
rotization and the formation of internal cuticular rid
g
es. In some apter
yg
otes, for example,
t
wo small, crescent-shaped pleural sclerites ma
y
be seen above the coxa, thou
g
h the rest of
th
e
pl
euron
i
s mem
b
ranous. In t
h
e
p

rot
h
orax o
f
P
l
eco
p
tera t
h
ere are
lik
ew
i
se two sc
l
er
i
tes
,
b
ut t
h
ese are muc
hl
arger t
h
an t
h
ose o

f
apterygotes an
d
occupy more t
h
an
h
a
lf
t
h
ep
l
eura
l
area. In t
h
et
h
orac
i
cse
g
ments o
f
a
ll
ot
h
er pter

yg
otes t
h
ep
l
eura are
f
u
lly
sc
l
erot
i
ze
d
an
d
ar
e
7
4
CHAPTER
3
F
IGURE 3.18. (A) Dorsa
l
v
i
ew o
f

a genera
li
ze
d
a
li
notum; an
d
(B)
l
atera
l
v
i
ew o
f
a typ
i
ca
l
w
i
ng-
b
ear
i
n
g
se
g

ment. [From R. E. Sno
dg
rass, Princip
l
es of Insect Morp
h
o
l
ogy .
C
op
y
ri
g
ht 193
5
b
y
McGraw-Hill, Inc. Used
w
ith permission of McGraw-Hill Book Company.]
a
ddi
t
i
ona
ll
y strengt
h
ene

db
yt
h
e
f
ormat
i
on o
f
an
i
nterna
l
pl
eura
l
ri
dg
e t
h
at exten
d
s
d
orsa
lly
i
nto t
he
p

l
eura
l
win
g
proces
s
(F
i
gure 3.18B). Art
i
cu
l
at
i
ng w
i
t
h
t
hi
s process
i
st
h
e
s
econ
d
axillary sclerite

.
Each pleural rid
g
e is extended inwardl
y
as a
p
leural arm
(
Fi
g
ure 3.19
)
that meets and ma
y
fuse with similar apoph
y
ses from the sternum. The pleural rid
g
ei
s
seen externally as th
e
pleural sulcu
s
(
Figure 3.18B) above the coxa. This groove divides
t
h
ep

l
euron
i
nto an anter
i
o
r
ep
i
sternu
m
a
n
d
poster
i
or ep
i
mero
n
.
Of
ten t
h
ese sc
l
er
i
tes ar
e

di
v
id
e
d
secon
d
ar
il
y
i
nto
d
orsa
l
an
d
ventra
l
areas, t
he
s
u
p
rae
p
isternu
m
a
n

d
i
n
f
raepisternum
,
and
s
u
p
rae
p
imero
n
a
n
d
infraepimero
n
. Derived from the episternum and epimeron and ap
-
pearin
g
above them usuall
y
as distinct, articulated sclerites are the basala
r
a
n
d

s
ubala
r
,t
o
w
hich important win
g
muscles are attached.
In t
h
et
h
orax t
h
e acrostern
i
te o
f
t
h
e typ
i
ca
l
secon
d
ary segment
f
orms an

i
n
d
epen
d
en
t
i
ntersegmenta
l
p
l
ate or
i
nter
s
ternite.T
h
e
i
nterstern
i
tes, w
hi
c
h
are
f
oun
db

etween t
h
e pro
-
an
d
mesot
h
orax an
db
etween t
h
e meso- an
d
metat
h
orax
,
are
k
nown a
s
sp
inasterna
b
ecause
e
ach bears an internal spine to which a few ventral muscles are attached. Frequentl
y
,th

e
spinasterna fuse with the se
g
mental plate, eus
t
ernum
,
of the precedin
g
se
g
ment. The euster-
n
um
i
s a compos
i
te structure, compr
i
s
i
ng t
h
e primar
y
sterna
l
p
l
ate

a
n
d the
s
ternop
l
eurite
.
T
h
e eusternum may
b
e
di
v
id
e
d
secon
d
ar
il
y
i
nto an anter
i
or
b
a
s

i
s
ternu
m
a
n
d
poster
i
or
s
ter-
ne
ll
um
by
t
he
s
ternaco
s
ta
ls
u
l
cu
s
(F
ig
ure 3.20). T

h
e
l
atter
i
st
h
e resu
l
to
f
an
i
nva
gi
nat
i
on t
o
f
orm the s
t
ernacos
t
a
,a
r
id
g
e of cuticle that unites th

e
s
ternal apophyse
s
(Fi
g
ure 3.19). In the
hi
g
her pter
yg
otes these apoph
y
ses are borne on a median internal rid
g
e and form a Y-shape
d
f
urca (Figure 3.19). As noted earlier, these apophyses combine with the pleural arms to for
m
ar
i
g
id i
nterna
l
support. T
h
e
l

atter prov
id
es attac
h
ment
f
or t
h
ema
j
or
l
ong
i
tu
di
na
l
ventra
l
m
usc
l
es an
d
certa
i
n musc
l
es o

f
t
h
e
l
eg
.
It must beemphasized that man
y
variations occurfrom the rather
g
eneral description of
a
thoracic se
g
ment provided above. In all insects the prothorax is modified b
y
the development
75
E
XTER
NAL
S
TRUCTURE
F
I
GU
RE 3.19
.
Diagrammatic cross-sections of the thorax to show the endoskeleton. (A) Normal condition; and

(
B) con
di
t
i
on w
h
en
f
urca present. [From R. E. Sno
d
grass,
P
rincip
l
es of Insect Morp
h
o
l
ogy .
C
opyright 1935 b
y
M
cGraw-H
ill
, Inc. Use
d
w
i

t
h
perm
i
ss
i
on o
f
McGraw-H
ill
Boo
k
Compan
y
.]
F
I
GU
RE 3.20.
V
entral view of a generalized thoracic sternum. [From R. E. Snodgrass,
P
rinciples o
f
Insec
t
Morp
h
o
l

ogy
.
Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]
of the neck re
g
ion. The
p
rono
t
u
m
especiall
y
is different, lackin
g
the antecostal re
g
ion and
phra
g
ma throu
g
h neck membranization. In some
g
roups (e.
g
., Orthoptera, Hemiptera, and
Co
l
eoptera) t

h
e pronotum
i
s great
l
yen
l
arge
d
;
i
not
h
ers
i
t
i
sre
d
uce
d
to a narrow
b
an
d
b
etween t
h
e
h

ea
d
an
d
mesot
h
orax. In t
h
ose or
d
ers w
h
ose mem
b
ers
h
ave a s
i
ng
l
epa
i
ro
f
f
unct
i
ona
l
w

i
n
g
s, t
h
e ter
g
a
l
p
l
ates o
f
t
h
ese
g
ment
f
rom w
hi
c
h
t
h
ew
i
n
g
s are a

b
sent ar
e
u
suall
y
reduced in size
.
4.3. Thoracic Appendage
s
4
.
3
.
1
.Le
g
s
I
nt
h
e vast ma
j
or
i
ty o
fi
nsects eac
h
t

h
orac
i
c segment
b
ears a pa
i
ro
fl
egs. In t
h
e cases
w
here le
g
s are absent, for example, in all dipteran, and man
y
coleopteran and h
y
menoptera
n
larvae, the condition is secondar
y
.T
y
picall
y
, the le
g
s are concerned with walkin

g
and
runnin
g
, but the
y
ma
y
be specialized for a ran
g
e of other ph
y
sical functions, some o
f
whi
c
h
are
d
escr
ib
e
db
e
l
ow.Ina
ddi
t
i
on,

f
or many
i
nsects t
h
ey are
i
mportant organs o
f
tast
e
7
6
CHAPTER
3
F
I
GU
RE 3.21. (A) H
y
pothetical
g
round plan of le
g
podites in ancestral insect; and (B) t
y
pical le
g
of a modern
i

nsect.
[
A, after J. Kukalov
a-Peck, 1987, New Carboniferous Diplura, Monura, and Thysanura, the hexapod
´
g
roun
d
p
l
an, an
d
t
h
ero
l
eo
f
t
h
orac
i
cs
id
e
l
o
b
es
i

nt
h
eor
igi
no
f
w
i
n
g
s (Insecta), Can. J
.
Z
oo
l
.
65
:
2327–234
5
.B
y
permission of the National Research Council of Canada and the author. B, from R. E. Snod
g
rass,
P
rinciples o
f
I
nsect Morpholo

gy.
Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.
]
(
see C
h
apter 12, Sect
i
on 4.1). As note
d
ear
li
er, Ku
k
a
l
ov´a-Pec
k
(1987) su
gg
este
d
t
h
at t
h
e
ancestral limb included 11 podites, as well as exites and endites (Fi
g
ure 3.21A). Because o

f
f
usion of podites with the pleuron or with ad
j
acent podites the full complement of podites in
t
h
e
l
eg
i
s never seen, t
h
oug
hi
n many
f
oss
il
san
d
a
f
ew extant Ep
h
emeroptera an
d
O
d
onata

as many as e
i
g
h
tpo
di
tes can
b
e
id
ent
ifi
e
d
.
T
ypical Walkin
g
Le
g
.
T
he le
g
consists of six podites, the coxa, trochanter, femur,
tibia, tarsus, and pretarsus (Fi
g
ure 3.2lB). Between ad
j
acent parts are a narrow, annulated

m
embrane, the
co
r
ium
, and usuall
y
a mono- or dicond
y
lic articulation
.
Th
e coxa
i
sas
h
ort, t
hi
c
k
segment strengt
h
ene
d
at
i
ts prox
i
ma
l

en
db
yan
i
nterna
l
r
id
ge,
t
h
e
b
a
s
ico
s
ta (F
i
gure 3.22). T
h
e coxa usua
ll
y
h
as a
di
con
d
y

li
c art
i
cu
l
at
i
on w
i
t
h
t
h
ep
l
euron.
In some or
d
ers t
h
e
b
a
s
ico
s
ta
ls
u
l

cu
s
i
sU-orV-s
h
ape
d
over t
h
e poster
i
or
h
a
lf
o
f
t
h
e coxa
(
Fi
g
ure 3.22). The sclerite thus demarcated becomes thickened and is known as th
e
meron
.
The trochanter is a small se
g
ment. It alwa

y
s has a dicond
y
lic articulation with the coxa but
i
s usua
ll
y
fi
rm
l
y
fi
xe
d
to t
h
e
f
emur, w
hi
c
hi
s genera
ll
yt
h
e
l
argest

l
eg segment. Fo
ll
ow
i
ng
t
h
es
l
en
d
er t
ibi
a
i
st
h
e tarsus, a segment t
h
at
i
s usua
ll
ysu
bdi
v
id
e
di

nto
b
etween two an
d
fi
v
e
tar
s
omere
s
a
n
d
a pretarsus. T
h
e pretarsus,
i
n most
i
nsects, ta
k
es t
h
e
f
orm o
f
apa
i

ro
f
tarsal claw
s
a
nd a median lobe
,
th
e
a
r
oliu
m (Fi
g
ure 3.23).
77
E
XTER
NAL
S
TRUCTURE
F
I
GU
RE 3.22
.
Structure of the coxa. (A) Lateral view; and (B) coxa with a well-develo
p
ed meron. [From
R

. E. Snodgrass, Principles o
f
Insect Morphology
.
C
opyright 1935 by McGraw-Hill, Inc. Used with permission
o
f
McGraw-H
ill
Boo
k
Compan
y
.
]
F
I
GU
RE 3.23. Distal part of a leg showing the arolium and claws.
[
From R. E. Sno
d
grass,
P
rincip
l
es of Insect Morp
h
o

l
ogy .
C
opyr
i
g
h
t
193
5
b
y
McGraw-Hill, Inc. Used with permission of McGraw-Hil
l
B
ook Company.
]
L
e
g
Modifications. T
h
e
f
unct
i
ons
f
or w
hi

c
h
t
h
e
l
egs
h
ave
b
ecome mo
difi
e
di
nc
l
u
d
e
j
umpin
g
, swimmin
g
,
g
raspin
g
,di
gg

in
g
, sound production, and cleanin
g
.
I
n Orthoptera and a few Coleoptera (e.
g
., flea beetles) the femur on the hindle
g
is
g
reatl
y
enlarged to accommodate the extensor muscles of the tibia used in jumping. In swimming
i
nsects, t
h
et
ibi
aan
d
tarsus o
f
t
h
e
hi
n
dl

egs (occas
i
ona
ll
ya
l
so t
h
em
iddl
e
l
egs) are
fl
attene
d
an
db
ear r
i
g
id h
a
i
rs aroun
d
t
h
e per
i

p
h
ery (F
i
gure 3.24A). Legs mo
difi
e
df
or grasp
i
ng ar
e
f
oun
di
n pre
d
aceous
i
nsects suc
h
as t
h
e mant
i
san
dgi
ant water
b
u

g
,
i
n ectoparas
i
t
i
c
li
ce,
and in males of various species where the
y
are used for han
g
in
g
onto the female durin
g
matin
g
. In the mantis, the tibia and femur of the forele
g
are equipped with spines and operate
t
oget
h
er as p
i
ncers (F
i

gure 3.24B). T
h
e
f
ore
l
eg o
f
a
l
ouse
i
ss
h
ort an
d
t
hi
c
k
an
dh
as at
i
ts t
i
p
a
si
ng

l
e,
l
arge tarsa
l
c
l
aw t
h
at
f
o
ld
s
b
ac
k
aga
i
nst t
h
et
ibi
a
l
process (F
i
gure 3.24C). Suctor
i
a

l
pa
d
s
h
ave
b
een
d
eve
l
ope
d
on t
h
e
f
ore
li
m
b
s
i
nma
l
es o
f
man
yb
eet

l
e spec
i
es. In D
y
tiscu
s
,
for example, the first three tarsomeres are flattened and possess lar
g
e numbers of cuticula
r
7
8
CHAPTER
3
F
IGURE 3.24.
L
eg modifications. (A) Hindleg o
f
Gy
rinus (swimming); (B) foreleg of a mantis (grasping prey)
;
(C)
f
ore
l
eg o
f

a
l
ouse (attac
h
ment to
h
ost); (D)
f
ore
l
eg o
f
D
ytiscus (
h
o
ldi
ng onto
f
ema
l
e); an
d
(E)
f
ore
l
eg o
f
amo

le
c
r
i
c
k
et (
diggi
n
g
). [A, a
f
ter L. C. M
i
a
ll
, 1922
,
T
h
e Natura
l
History of A
q
uatic Insect
s
,
pu
bli
s

h
e
dby
Macm
ill
a
n
Ltd. B, D, E, after J. W. Folsom, 1906
,
E
ntomology: With Special Re
f
erence to Its Biological and Economi
c
A
spects
.]
c
ups, two o
f
w
hi
c
h
are extreme
l
yen
l
arge
d

(F
i
gure 3.24D). T
h
e
f
ore
l
egs o
f
so
il
-
d
we
lli
n
g
i
nsects suc
h
as t
h
emo
l
ecr
i
c
k
et (F

i
gure 3.24E), c
i
ca
d
as, an
d
var
i
ous
b
eet
l
es are mo
difi
e
df
or
diggi
n
g
.T
h
e
l
e
g
s are
l
ar

g
e,
h
eav
ily
sc
l
erot
i
ze
d
,an
d
possess stout c
l
aws. T
h
e tarsomeres ar
e
reduced in number or ma
y
disappear entirel
y
in some forms. In man
y
Orthoptera sound
s
are produced when the hind femora, which have a row of cuticular pe
g
s on their inne

r
sur
f
ace, are ru
bb
e
d
aga
i
nst r
id
ge
d
ve
i
ns on t
h
e
f
ore w
i
ng. Mo
difi
cat
i
ons to t
h
e
f
ore

l
egs
f
o
r
cl
ean
i
ng purposes are
f
oun
di
n many
i
nsects. In certa
i
nCo
l
eoptera an
d
Hymenoptera,
f
o
r
e
xample, the hone
y
bee (Fi
g
ure 3.2

5
A), a notch lined with hairs occurs on the metatarsus
79
E
XTER
NAL
STRUCTURE
F
I
GU
RE 3.25. Le
g
mo
difi
cat
i
ons
i
nt
h
ewor
k
er
h
one
yb
ee. (A) Fore
l
e
g

s
h
ow
i
n
g
t
h
ec
l
ean
i
n
g
notc
h
, (B) oute
r
s
urface of hindleg showing the pollen basket, and (C) inner surface of hind tarsus and tip of hind tibia showing
r
ake and pollen press. [After R. E. Snodgrass, 1925.
A
natomy an
d
P
h
ysio
l
ogyoft

h
e Honey
b
e
e
,
McGraw-H
ill
B
oo
k
Compan
y
.
]
o
f
t
h
e
f
ore
l
eg t
h
roug
h
w
hi
c

h
t
h
e antenna can
b
e
d
rawn an
d
c
l
eane
d
.T
h
e
hi
n
dl
egs o
f
t
h
e
b
e
e
are modified for pollen collection (Figure 3.2
5
B). Rows of hairs, th

e
com
b
,
o
n
t
h
e
i
nner s
ide
o
f
t
h
e
fi
rst tarsomere scrape po
ll
en o
ff
t
h
ea
bd
omen. T
h
e
r

a
k
e
,
a
f
r
i
n
g
eo
fh
a
i
rs at t
h
e
di
sta
l
end of the tibia, then collects the pollen from the comb on the opposite le
g
and transfers i
t
t
o the
p
ollen
p
re

ss
.
When the
p
ress is closed, the
p
ollen is
p
ushed u
p
into the
p
olle
n
baske
t
,
w
here it is stored until the bee returns to its nest.
4
.3.2. W
i
ng
s
The ma
j
orit
y
of adult Pter
yg

ota have one or two pairs of functional win
g
s. The complete
absence of win
g
s is a secondar
y
condition, associated with the habits of the
g
roup concerned,
for example, soil-dwellin
g
or endoparasitism. The win
g
sma
y
be modified for a variet
y
of
purposes ot
h
er t
h
an
fli
g
h
t
.
D

evelo
p
ment and General
S
tructure
.
R
egar
dl
ess o
fi
ts evo
l
ut
i
onary or
i
g
i
n(C
h
ap
-
t
er 2, Section 3.1) a win
g
contains the usual inte
g
umental elements (cuticle, epidermis, an
d

80
CHAPTER
3
basal lamina) and its lumen, bein
g
an extension of the hemocoel, contains tracheae, nerves,
and hemol
y
mph. As the win
g
develops, the dorsal and ventral inte
g
umental la
y
ers becom
e
c
losel
y
apposed over most of their area formin
g
the
w
ing membran
e
.
The remainin
g
areas
f

orm c
h
anne
l
s, t
h
e
f
uture
v
e
i
n
s
,
in
whi
c
h
t
h
e nerves an
d
trac
h
eae may occur. T
h
e cut
i
c

l
e sur-
roun
di
ng t
h
eve
i
ns
b
ecomes t
hi
c
k
ene
d
to prov
id
e strengt
h
an
d
r
i
g
idi
ty to t
h
ew
i

ng. Ha
i
rs o
f
two t
y
pes ma
y
occur on t
h
ew
i
n
g
s:
mic
r
ot
r
ichia
,
w
hi
c
h
are sma
ll
an
di
rre

g
u
l
ar
ly
scattere
d
,
and
mac
r
ot
r
ic
h
ia
,
which are lar
g
er, socketed, and ma
y
be restricted to veins. The scales
o
f Lepidoptera and Trichoptera are hi
g
hl
y
modified macrotrichia. For a detailed review of
wi
ng morp

h
o
l
ogy, see Wootton (1992).
It must
b
e assume
d
t
h
at t
h
e extreme
l
yvar
i
e
d
arrangement o
f
ve
i
ns
f
oun
d
among t
h
e
i

nsect or
d
ers
i
s
d
er
i
ve
df
romapr
i
m
i
t
i
ve common pattern, t
h
e groun
d
p
l
an or arc
h
etype
v
enation. Details of the latter will never be known with certaint
y
because even the earliest
f

ossilized win
g
shadahi
g
hl
y
complex venation. In order to develop a basic plan of win
g
v
enation, it is necessary to compare (and homologize) not only the veins, but also flexion
li
nes (
li
nes a
l
ong w
hi
c
h
aw
i
ng creases
d
ur
i
ng
fli
g
h
t),

f
o
ld li
nes (w
h
ere w
i
ngs crease
d
ur
i
ng
f
o
ldi
ng), an
d
w
i
ng areas (areas
d
e
li
m
i
te
db
y spec
ifi
cve

i
ns an
d
/or
li
nes) (Wootton, 1979)
.
Given the diversit
y
of win
g
s of insects, both fossil and extant, it is not surprisin
g
that author
s
have sometimes reached quite different conclusions with respect to the homolo
g
ies of veins
(
compare Figures 2.2 and 3.26). This is unfortunate given the enormous importance of win
g
v
enat
i
on
i
np
h
y
l

ogenet
i
can
d
taxonom
i
c stu
di
es
.
Th
e usua
l
met
h
o
d
o
fd
eterm
i
n
i
ng
h
omo
l
ogy
i
s

di
rect compar
i
son o
f
t
h
e pos
i
t
i
on an
d
f
orm of veins. In addition, there are other, more subtle features with which to assess potential
homolo
g
ies (Ra
gg
e, 1955; Hamilton, 1972a; Lawrenc
e
et al.
, 1991
)
. Thus, certain veins
are alwa
y
s associated with particular axillar
y
sclerites. Till

y
ard (1918) made use of the fact
F
I
GU
RE 3.26
.
Bas
i
csc
h
eme o
f
w
i
n
g
venat
i
on,
fl
ex
i
on
li
nes an
df
o
ldi
n

gli
nes. (A) Fore w
i
n
g
or
hi
n
d
w
i
n
g
w
i
t
h
out
v
annus; and (B) vannal area of hind wing. [After R. J. Wootton, 1979, Function, homology and terminology i
n
i
nsect w
i
ngs, Syst. Entomo
l
.
4
:
81–93. By perm

i
ss
i
on o
f
t
h
eRoya
l
Entomo
l
og
i
ca
l
Soc
i
ety.
]
81
E
XTER
NAL
S
TRUCTURE
t
hat some veins have associated with them a row of macrotrichia. In man
y
win
g

s this row
persists even when the ori
g
inal vein has disappeared. The widel
y
used Comstock-Needham
s
y
stem of win
g
venation was based on the assumption that tracheae are alwa
y
s present
i
n
p
art
i
cu
l
ar ve
i
ns an
d
t
h
at t
h
e
p

attern o
f
trac
h
eae
d
eve
l
o
p
s
i
nac
h
aracter
i
st
i
c manne
r
an
d
t
h
ere
b
y
d
eterm
i

nes t
h
e venat
i
ona
l
pattern (Comstoc
k
, 1918). In
f
act, t
h
e
l
acunae
f
rom
whi
c
h
ve
i
ns ar
i
se
d
eve
l
op as
h

emo
ly
mp
h
c
h
anne
l
san
di
t
i
son
ly
a
f
ter ve
i
ns
h
ave
f
orme
d
t
h
a
t
t
racheae and nerves extend into them. In addition, tracheal patterns ma

y
differ, for example,
b
etween pupal and adult instars, accordin
g
to different functional needs. Other authors have
b
ase
d
t
h
e
i
r stu
di
es o
f
ve
i
n
h
omo
l
ogy on w
i
ng
fl
ut
i
ng, t

h
ea
l
ternat
i
on o
f
concave an
d
convex
ve
i
ns. T
hi
s approac
hi
so
fli
m
i
te
d
use,
h
owever, an
di
s not app
li
ca
bl

eto
b
ranc
h
e
d
ve
i
n
systems w
h
ere
fl
ut
i
ng
i
s pract
i
ca
ll
y non-ex
i
stent, or to w
i
ngs t
h
at are secon
d
ar

il
y
fl
ute
d
(
Hamilton, 1972a
).
W
ootton (1979) made a ma
j
or contribution toward resolution of the confusion over th
e
nomenclature of veins and other wing components. His scheme, presented in Figure 3.26,
i
nc
l
u
d
es t
h
e
f
o
ll
ow
i
ng
l
ong

i
tu
di
na
l
ve
i
ns (
f
rom anter
i
or to poster
i
or):
c
o
s
t
a
,
s
u
b
co
s
ta
,
r
a-
d

iu
s
,
ra
d
ia
ls
ecto
r
,
anterior me
d
ia
,
p
osterior me
d
i
a
,
anterior cu
b
itu
s
,
p
osterior cu
b
itus
,

an
d
a
nals (of which there ma
y
be several). An
y
of these veins ma
y
be branched, thou
g
h the
costa and posterior cubitus rarel
y
are because the former is at the leadin
g
ed
g
e of the win
g
w
hile the latter is associated with the claval furrow. In wings with
a
j
ugu
m
(see below),
j
ugal
v

ein
(
s
)
may occur. T
h
ema
j
or
fl
ex
i
on
li
nes are t
he
m
e
d
ian flexion
l
in
e
,w
hi
c
h
or
i
g

i
nates
j
ust
b
e
hi
n
d
t
h
eme
di
aan
d
runs outwar
dj
ust
b
e
hi
n
d
t
h
era
di
a
l
sector, an

d
t
he
cl
ava
l
furrow
,
w
hich lies alon
g
the posterior cubitus (Fi
g
ure 3.27). Thou
g
h fold lines ma
y
be transverse,
as in the hind win
g
s of beetles and earwi
g
s, the
y
are normall
y
radial to the base of the win
g,
allowin
g

ad
j
acent sections of a win
g
to be folded over or under each other. The commonest
fold li
n
eisthe
j
uga
lf
o
ld
,s
i
tuate
dj
ust
b
e
hi
n
d
t
h
et
hi
r
d
ana

l
ve
i
n. In
hi
n
d
w
i
ngs w
i
t
h
a
n
F
I
GU
RE 3.27
.
Di
a
g
ram s
h
ow
i
n
g
t

h
ema
j
or areas, mar
gi
ns an
d
an
gl
es o
f
a
g
enera
li
ze
d
w
i
n
g
. (A) Fore w
i
n
g
o
r
h
ind wing without vannus; and (B) vannal area of hind wing [Partly after R. J. Wootton, 1979, Function, homolog
y

an
d
term
i
no
l
ogy
i
n
i
nsect w
i
ngs,
S
yst. Entomo
l.
4
:
81–93. By perm
i
ss
i
on o
f
t
h
eRoya
l
Entomo
l

og
i
ca
l
Soc
i
ety.]