134 ZOOLOGY. 
perfect insect appears. In some cases the larva resembles the adult at all 
times in most particulars; and when, after successive moultings, it becomes 
a pupa, this is still much like the adult, and continues to eat and move 
about, differing from the larva in having incipient wings inclosed in an 
envelope, and from the adult in not having perfect wings. Insects are thus 
subject to two principal kinds of metamorphosis, whence the latter have 
been named Homomorpha, and the former Heteromorpha. The metamor- 
phosis of the Lepidoptera, Coleoptera, Hymenoptera, and Diptera, is 
heteromorphic; whilst that of the Orthoptera and Hemiptera is homo- 
morphic. 
Heteromorphic larvee are more or less cylindrical, with or without is, 
and a distinct head. They have generally thirteen segments, each of =i 
has been provided with a name by Newman, as follows, commencing with 
the head: 1, caput; 2, prothorax; 3, mesothorax; A, Le 3 5, pro- 
podeon ; 6, podeon, 7, metapodeon; 8, octoon; 9, ennaton; 10, decaton; 
11, protelum; 12, paratelum, 18, telum. 
The head of larvee is in some cases not different from the other segments, 
being equally soft, and without antenne, eyes, or jaws. <A larva of this 
kind (the feet we also absent) is popularly termed a maggot. The cater- 
pillars, which hee a more perfect organization, have a corneous head 
generally bearing the various organs apparent in the perfect insect or imago. 
The antenne of larve have a simple.structure, and but few articulations, 
even in those cases where the adult has them complicated and very long. 
Of the two kinds of eyes found in adult insects, compound and simple, the 
latter, named stemmata, are alone present in the larvae, but these are some- 
times entirely destitute of visual organs. When present, there are from 
one to six upon each side. Some caterpillars have the power of secreting 
a silken thread, out of which their cocoon is made, the secreting organ being 
a part of the mouth. The larve of some Coleoptera have an analogous 
organ at the posterior extremity. 
The sides of terrestrial larvee generally show the spiracles, which usually 
amount to nine or ten upon each side. All the segments, except the first, 
or head, third, fourth, and last, are usually supplied with spiracles. In some 
aquatic larvee there are lateral gills, and in others breathing is accomplished 
through the posterior extremity. 
The Jarva state is that in which insects generally live the longest, the life 
of the imago being often very short ; so short, that in some cases they require 
no nourishment, and are not provided with a mouth. Some species of 
Melolontha live a few weeks in the adult state, and three years as larve. 
Cicada septendecim (and probably other species) does not survive a single 
season, although its larva is seventeen years in coming to maturity. 
Pupa. In the homomorphous forms the passage from the larva to the 
pupa state is gradual, and is accompanied by but little external change, 
especially in the wingless forms, as bed-bugs, and certain grasshoppers. 
Amongst the latter, ‘he different stages of the genus Phalangopsis can 
hardly be pipe 9 but we have observed that certain spines upon the 
legs appear only in the last stage, thus indicating the adult. 
338 
