168 
NATURE 
that of insects, have probably come to be what they are, 
assuming them to have developed under natural laws 
from simpler organisms, The question is one of great 
difficulty. It is hardly necessary to say that insects cannot 
have passed through all the lower forms of animal life, 
and the true line of their development would not at pre- 
sent be agreed upon by all naturalists. In this question 
embryology and development are perhaps our best guides. 
The various groups of Crustacea, for instance, greatly as 
they differ in their mature condition, are for the most 
part very similar when they quit the egg. Haeckel, in his 
“Naturliche Schopfungsgeschichte,” gives a diagram 
which illustrates this very clearly. 
In the case of insects, the gradual course of evo- 
lution through which the present condition of the 
group has been probably arrived at, has been discussed 
by Mr. Darwin, by Fritz Miller, Haeckel, Brauer, myself 
and others. At first sight the differences are indeed great 
between the various groups of insects. The stag beetle, 
the dragon fly, the moth, the bee, the ant, the gnat, the 
grasshopper —these and other less familiar types seem at 
first to have little indeed in common. They differ in size, 
a 
Fic. 60, Egg of Tardigrade, Kaufmann, Zeit f. Wiss. Zool. 1851, Pl. r 
61, Egg of Tardigrade after the yolk has subdivided. 62, Egg of 
Tardigrade in the next stage. 63, Egg of Tardigrade more advanced. 
in form, in colour, in habits, and modes of life. Yet the 
researches of entomologists, following the clue supplied 
by the illustrious Savigny, have shown, not only that 
while differing greatly in details, they are constructed on 
one common plan; but also that other groups, as for 
instance, Crustacea (Lobsters, Crabs, &c.) and Arachnida 
(Spiders and Mites), can be shown to be fundamentally 
similar, In Pl. 4 I have figured the larve of an Ephemera 
(Fig. 1), of a Meloe (Fig. 2), of a Dragon Fly (Fig. 3), of 
a Sitaris (Fig. 4), of a Campodea (Fig. 5), of a Dyticus 
(Fig. 6), of a Termite (Fig. 7), of a Stylops (Fig. 8), and 
of a Thrips (Fig. 9). All these larvee possess many cha- 
racters in common, The mature forms are represented 
in the corresponding figures of Plate 3, and it will at once 
be seen how considerably they differ from one another. The 
same fact is also illustrated in Figs. 48—55, where Figs. 
48—5SI represent the larval states of the mature forms re- 
presented in Figs.52—55. Fig. 48is the larva of a moth, 
Agrotis suffusa (Fig. 52); Fig. 49 of a beetle, Haltica 
(Fig. 53); Fig. 50 of a Saw Fly, CimseaXFig. 54) ; and 
Fig. 51 of a Centipede, ¥z/us (Fig. 55). 
Thus then, although it can be demonstrated that per- 
fect insects, however much they diifer in appearance, are 
yet reducible to one type, the fact becomes much more 
evident if we compare the larva. M. Brauer* and I t+ 
have pointed out that two types of larvae, which Packard 
has proposed to call the Eruciform and Leptiform, run 
through the principal groups of insects. This is obviously 
a fact of great importance: as all individual Meloés are 
derived from a form resembling Plate 2, Fig, 2, it is surely 
no rash hypothesis to suggest that the genus itself may 
be so. 
Firstly, however, let me say a word as to the general 
Insect type. It may shortly be described as consisting 
of animals, possessing a head, with mouth-parts, eyes, 
and antennz ; a thorax made up of three segments, each 
with a pair of legs; and a many-segmented abdomen 
with anal appendages. Into the internal anatomy I will 
* Wien. Zool. Bot. Gessels, 1869. 
- t Linnean Transactions, 7863, 
‘not now enter. 
| presenting the larva of a small beetle named Sitaris, 
It will be seen that Plate 4, Fig. 4, re- 
answers very well to this description. Many other 
Bectles are developed from larvz closely resembling those 
of Meloé (Plate 4, Fig. 2), and Sitaris (Plate 4, Fig. 4) ; in 
fact—except those species the larve of which, as, for 
instance of the Weevils (Plite 2, Fig. 6), are internal 
feeders, and do not require legs—we may say that the 
Coleoptera generally are derived from larvae of this type. 
I will now pass to a second order, the Neuroptera. 
Plate 4, Fig. 1, represents the larva of Chloéon, a species 
the metamorphoses of which [ described some years ago 
in the Linnean Transactions,* and itis obvious that in 
essential points it closely resembles the form which I 
have just described. 
The Orthoptera, again, the order to which Grass- 
hoppers, Crickets, Locusts, &c. belong, commence life in 
a similar condition, and the same may also be said of the 
Trichoptera. 
From the difference in external form, and especially 
the large comparative size of the abdomen, the larvze of 
Lepidoptera (Fig. 48), and of certain Hymenoptera, 
for instance, of Sirex (Fig. 14) and Tenthredo, the Saw 
Flies (Fig. 50), have generally been classed with the 
maggots of Flies, Bees, Weevils, &c., rather than with the 
more active form of larva just adverted to. This seems to 
me, as I have already pointed out,t to be amistike. If 
we look, for insiamce, at the larva of Tenthredo 
the three thoracic segments well marked,” 
we see 
and the three pairs of legs. The abdominal prolegs, 
indeed, give the larvae a very different appearance to those 
of the preceding type, but in some resp2cts remove them | 
still further from the apod, vermiform, larve. The larva 
of other species bel nging to this group, for instance of 
Lyda, have no abdominal prolegs, and well developed 
though short antenne. The caterpillar type differs 
then in its general appearance owing to its greater 
clumsiness, but still essentially agrees with that already 
described. 
No Dipterous larva, so far as I know. belongs truly to 
this type; in fact, the early stages of the pupa in the 
Diptera seem in some respects to correspond to the larva 
of other Insect orders. The Development of the Diptera 
is, however, as Weissman f has shown, very abnormal in 
other respects. 
Thus then we find in many of the principal groups 
of insects that, greatly as they differ from one another 
in their mature condition, woen they leave the egg 
they consist of a head; a three-segmented thorax, 
with three pairs of legs; and a many-jointed abiomen, 
often with anal appendages. Now is there any mature 
animal which answers to this description? We need 
not have been surprised if this type, through which 
it wouli appear that insects must have passed so 
many ages since (for winged Neuroptera have been 
found in the carboniferous strata) had long ago become 
extinct. Yet itis not so. The interesting genus Campo- 
dea (Pl. 3, Fig 5) still lives; it inhibits damp earth, and 
closely resembles the larva of Chloéon (PI. 2, Fig. 1), 
constitutinz, indeed, a type which, as shown in Pl. 4, 
Occurs in many orders of insects. It is true that the 
mouth parts of Campodea do not resemble either the 
strongly mandibulate form which prevails among the 
larvae of Coleoptera, Orthoptera, Neuroptera, Hymenop- 
tera, and Lepidoptera; or the suctorial type of the 
Homoptera and Heteroptera. It is, however, not the 
less interesting or significant on that account, since, as I 
have elsewhere endeavoured to point out, its mouth parts 
are intermediate § between the mandibulate and haustillate 
types ; a fact which seems to me highly significant. 
It seems to me, then, that there are good grounds for 
* Linnean Transactions, 1866, vol. xxv. 
+ Linnean Transactions, vol. xxiv. p 65. - 
1 Siebold and Kolliker’s Zeits. f Wiss. Zool., 1864. 
§ Journal, v, xis 
[Fune 26, 1873 
