The Life-Story of Insects

ory of the race as it might be traced through innumerable generations. The endless variety in the form and habits of insect-larvae and their adaptations to various mode

of orders and classes evidently akin to each other, furnish at least some indications of the course of development in the greater systematic divisions, even as the facts of seasonal dimorphism, mentioned in the last chapter, give hi

extinct types of hard-shelled marine animals, such as the Mollusca, fossil insects are few, as could only be expected, seeing that insects are terrestrial and aerial creatures with slight chance of preservation in sediments f

of Geological S

eriod of the Coal Measures, can only be a matter of inference. Still it may safely be inferred that when the structure of these remains clearly indicates affinity to some existing order or family, the life-history of the ext

nsects with complete transformations must have been fairly abundant. Rocks of Triassic age have yielded beetles and lacewing-flies, while from among Jurassic fossils specimens have been described as representing most of our existing orders, including Lepidoptera, Hymenoptera and Diptera. In Cainozoic rocks fossil insects of nearly six thousand species have been found, which are easily referable to existing families and often to existing genera. We may conclude then, imperfect though our knowledge of extinct insects is, that some of the most complex of insect life-stories were being worked out before the dawn of the Cainozoic era. Some instructive hints as to differences in the rate of change among different insect groups may be drawn from the study o

ew Brunswick, Canada, by some modern geolo

and what might have been expected, but we are confronted with the difficulty that if the most highly organised insects pass through the most profound transformations, then insects present a remarkable and puzzling exception to the general rules of development among animals, as has already been pointed out in the first chapter of this volume (p. 7). A few students of insect transformation have indeed supposed that the crawling caterpillar or maggot must be regarded as a larval stage which recalls the worm-like nature of the supposed far-off ancestors of insects generally. Even in Poulto

d difference in form between the newly-hatched young and the adult, and in such cases we find that the young insect lives in the same way as the adult, has the same surroundings, eats the same food. This is the rule (see Chapters II and III) with the Apterygota, the Orthoptera, and most of the Hemiptera. In the last-named order, however, we find in certain fam

gills, adapting them to an aquatic life, the stone-fly nymphs differ but slightly from the adults; the grubs of the dragon-flies and may-flies, however, are markedly different from their parents. In connection with these comparisons, it is to be noted that the dra

. A. Lameere has indeed, while admitting the adaptive character of insect larvae generally, argued (1899) with much ingenuity that the eruciform or vermiform type must have been primitive among the Endopterygota, believing that the original environment of the larvae of the ancestral stock of all these insects must have been the interior of plant tissues. He is thus forced to the necessity of suggesting that the campodeiform larvae of ground-beetles or lacewings must be regarded as due to secondarily acquired adaptations; 'they resemble Thysanura and the larvae of Heterometabola only as whales resemble fishes.' There are two considerations w

nd Galerucella) together with their grubs, all greedily eating the foliage; or lady-bird beetles (Coccinella) and their larvae hunting and devouring the 'greenfly.' All of these insects are, however, Coleoptera, and the adult insects of this order are much more disposed to walk and crawl and less disposed to fly than other endopterygote insects. Their heavily armoured bodies and their firm shield-like forewings r

ble of changing so as to suit the most diverse surroundings. In a most suggestive recent discussion on the transformation of insects P. Deegener (1909) has claimed that the larva must be regarded as the more modified stage, because while all the adult's structures are represented in the larva, even if only as imaginal buds, there are commonly present in the larva special adaptive organs not found in the imago, for example the pro-legs of caterpillars or the skin-gills of midge-grubs. The correspondence of parts in butterfly and caterpillar just referred to, may still be traced, though less easily, in bluebottle and maggot. The latter is an extreme example of degenerative evolution, and its contrast with the elaborately organised two-w

2). Reference has already been made to insects of various orders in which one sex is wingless, the Vapourer Moth (p. 96) for example, or all the individuals of both sexes are wingless, as the aberrant cockroaches mentioned in Chapter II (p. 15), or certain generations of virgin females are wingless, for example aphids (pp. 18-19) and gall-flies (pp. 94-5). Insects may thus become secondarily wingless, that is to say be manifestly the offspring of winged parents, and such wingless forms may on the other hand give rise to offspring or descendants with well-developed wings. Frequently, as in the case of the aphids, many wingless generations intervene between two winged generations. A striking illustration of this fact is afforded by an aquatic bug, Velia currens, commonly to be seen skating over the surface of running water. The adults of Velia are nearly always wingless, but now and then the naturalist meets with

is difficult to imagine in large groups during a prolonged evolutionary history, while the sudden appearance of a totally

ckard and other writers have stated that pupae of bees and wasps undergo two or three moults before the final exposure of the imago. Such an early pupal instar has been defined as a 'pro-nymph' or a 'semi-pupa.' Examples have been given of the exceptional passive condition of the penultimate instar in Exopterygota. The instars preceding this presumably had originally outward wing-rudiments in all insect life-histories, and the endopterygote condition was attained by the postponement of the outward appearance of these to successively later stages. The leg and wing rudiments of the male coccid (pp. 20-1) beneath the cuticle of the second instar are strictly comparable to imaginal buds, and these are present in one instar of what is generally regarded as an exopterygote life-history. The first instar in all insects has no visible wing-rudiments, but when they grow outwardly from the body, they necessarily become covered with cuticle, so that they must be visible after the first moult. There is no supreme difficulty in supposing that the important change was for these early rudiments to become sunk into the body, so that the cuti

rvae, which are carried on the abdominal segments somewhat as wings are on the thoracic segments. But B?rner has recently (1909) brought forward evidence that these abdominal gills really correspond serially with legs. Moreover Gegenbaur's theory suggests that the ancestral insects were aquatic, whereas the presence of tubes for breathing atmospheric air in well-nigh all members of the class, and the fact that aquatic adaptations, respiratory and ot

pects remain mysterious still. Perhaps the most striking result of the study of insect transformation is the appreciation of the divergent specialisation of larva and imago, and it is a suggestive thought that of the two the larva has in many cases diverged the more from the typical condition. The caterpillar crawling over the leaf, or the fly-grub swimming through the water, may thus be regarded as a creature preparing for a change to the true conditions of its life. It is a strange irony that the preparation

SSIFICATION

SECTA or

s A, Apt

r

a (Brist

la (Spri

s B, Exo

r

era (Ea

roaches, Grassho

ra (Ston

rmites or 'W

Copeognatha

ga (Biti

ptera (M

(Drago

ptera (

roptera (Bugs,

cads, 'Greenf

ura (

C, Endop

r

er-flies, Ant-l

era (Be

(Scorpio

ra (Caddi

(Moths and B

ies) Orthorrhapha (Cra

r-flies, House-fli

ptera (

a Symphyta

s, Ichneumon-flies,

GEOLOGICA

e fossils entombed in them, are arranged in 'descending' order, the more recent format

or Terti

stoc

oce

oc

ce

or Second

tac

ass

ass

c or Prim

rm

onif

oni

uri

bri

IOGR

ion, is needless to say very far from exhaustive. To save space, titles are often abbreviated. Most of the works in the general lis

NERAL

n der Insekten. Sitzb. d. Gesells

rwandlung der Insekten. Verhandl. der K.

. Insects, their Stru

. The Origin of

Die Metamorphose de

olsom. Entomo

undriss der Vergleiche

ch. Die fossilen

nneguy. Les In

nen Formen der Insectenmetamorph

des Metamorphoses chez les Insectes

Origin and Metamorphos

The Transformations o

ural History of Aqua

and Useful Insects.

Insects. Todd Cycl

d. Text book of En

es pour servir à l'Histoire naturell

Cambridge Natural Hi

Classification of Insects. I

Encycl. Brit. 10th E

er. Hexapoda in Encycl. Br

en (incorporates works on Insects publish

bald. Insect Pes

ECIAL

nswechsel den Eichen-Gallwespen. Ze

traton. Alternating

ations sur les Métamorphoses Inte

book of the Tsetse-Flies

fe-History of Agrionid Drag

t. Lepidoptera of the

rd. Les Insectes

cheenkiemen der Ephemeri

Monographie der

servir à l'histoire des Insectes foss

of Pupae of Heterocerous Lepido

sene Tracheensystem bei Insek

phose et les M?urs des Meloides. An

geschichte bei den Insekten. Zei

hose des Lepidoptères. Bull

Fortpflanzung einer Chironomus. Mem

ology of the Lepidoptera. Trans.

Larve von Tenebrio molitor. Sitzb. d,

ten Jugendformen von M

aedogenesis der Cecid

n and Species-forming of Ectopar

yonale Entwicklung der Musciden.

History of Common Animals (c

owne. The Blowfl

pment of Chloeon. Trans.

raité anatomique d

pighi. De Bo

eriodical Cicada. Entom. B

nal Dimorphism in Butterflies.

A. B. Hammond. The H

. Coccidae of the B

ur Morphologie des Tr

phology of the Lepidopterous Pupa

pidopterous Larvae &c. and their su

tion of Butterflies. Pr

. Report of Entomolog

und Anatomie des m?nnlichen Aspidi

Insekten in Zittel'

onale Entwicklung der Trichopteren

orfosi e Costumi della Le

e Plant-louse. New Jersey A

ere Metamorphose von Musca

r Felsenspringer, Machiloi

ren Gallmückenlarven. Zeits

itoxenia. Zeitsch. f.

nale Entwicklung der Musciden. Ze

amorphose von Co

heorie. Leipzig. (English Transla

N

E F G H

R S T U

ssulariata,

of larvae,

haga

r, H

dae, 27

idae,

s sege

11, 23, 47,

of generat

bola,

erygo

as,

lion

, 64

e, 17-

pomi

s-li

gota,

ects, 23-34

vana and var

a cai

iada

ropo

n, E.

ord, see L

-Browne

beetl

, C. G.

gard,

40, 46

50-7, 80, 1

Mot

-lic

h, 1

orienta

r-beet

ttle, 43, 44, 46,

, C.,

es, 73-

in,

, 6, 52, 5

le-ta

iart,

es, 1, 83

erflies, 39,

ge-fl

ies, 62-3

ic inse

, 43. See

rm larvae,

bida

erous in

a pomonel

n-beet

36, 49, 58-62,

yidae,

bycid

pods,

fer

, T. A.

us, 43,

oeo

, 82. See

, 53. See als

sopa

, 22,

ficati

ing Mo

eetles,

es-mo

e, 20,

nella

, 11, 14, 1

oon

g Moth

, 50-6, 80

embo

ion, 35, 107, 119. S

thra

38, 62

es, 67, 7

aste

acea,

, 43,

lioni

29, 37, 40, 5

94. See als

ong-leg

n, C.

er, P.

n insec

tz,

e system

s pyriv

, 67-79, 81, 86

en larva and ima

ed Lepidopte

ies, 26-3

-flie

life, 34,

icu

10. See a

rm, 9,

Moths,

26, 34, 65-7,

erid

a, 41, 49, 1

a, 24. See a

rmis,

tali

larvae, 56

n, 16, 1

a, 41, 108,

kele

, J.

body

iod, 27, 32

, 1, 4,

as,

-gut

pup

es, 64-6

dges, 6

n, M

hilus e

aur, C

history,

trida

27, 32, 78,

sini

orm, 5

, 43,

h, 38, 6

, J.,

pers, 11

m, O

beetles

wth

See also Cate

, 59,

A. R.,

rsch,

, Will

-Jackson

Mot

rt,

ode

robi

etabo

era, 1

y, L. F

, R., 6

. See Winte

-gut

bosci

is and His

etabo

ly, 67,

-flie

ra, 58, 6

tamorph

ma bovi

derm

-flies, 6

or discs, 34

24, 3

13, 33,

and larva, 2,

c insec

e, W

g, V.

vsky,

um,

g-flies

bird

re, A

yris

, 26-7, 32,

reprodu

mpidae,

r, O.

es, 53, 83

capular

36, 38, 49, 58

lulid

e,

urus

rn Bee

terpillar

, B.

k, J.,

triid

et,

ilis

, 67, 71-6

oth, 60,

phaga

4, 17, 26

el-f

t, C.

l, G. A

e, 2, 1

31-4, 107,

idae

c insec

bola

is (in gene

insects) 8, 3

28, 33, 43, 77,

. See Cu

58-62, 84,

10, 32,

domest

idae

cle

s syst

era, 57

t, G.,

idae,

, 15,

appl

t pup

. See also

us ov

etles,

antiq

era, 17

oths,

, A. S.

. See Larval

Lady But

oic ins

n, J.

nsects, 73-

al car

nogene

ansformati

la,

n inse

ocyt

decta,

otret

sicae, 39,

and var. bry

gaste

24. See also

lidae

E. B., 61

cis

trypid

, 4, 58-

mph, 1

e colorat

s chrysoc

idae

7, 40, 79-

rium

para

is car

led mag

A. F. de,

e larvae, 9

ctive o

aga hete

, C.

son, E

midge

opha

lies,

s, 20. See a

baeid

t, E.

ytid

r, S.

changes

dimorph

-pup

idae

ferences,

., 13, 3

ning, 58,

worm

pha

a, A.

tri, F

ium,

, J.

idae,

ngid

nere

, 23, 70, 72

g-tai

ies, 24,

ago, 3

g inse

rdam,

hus,

inae,

o molit

oxenii

ld, F.

anur

oths, 5

-beetl

idae

lida

ell Butter

icida

em. See Air-t

ion. See Me

c insec

hoce

ra, 62-3,

e Fli

fly, 53

p Mot

Moths,

urtica

ees,

Moth, 9

curren

ff, K.

rm larvae,

stem-mo

reproductio

er,

ly, 73-4

colora

nn, E

46, 64,

ts. See Aqu

vil

, A., 38

flies, 41, 8

-beetl

ects, 15, 18

20, 22, 24, 28, 33, 36

, 14, 11

brood

g stages

orms,

-was

Y JOHN CLAY, M.A. AT

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IDGE

CE AND L

he Cambridge U

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any in the Unive

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By Rev. C. H. W

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