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, diftering from the larva in having incipient wings inclosed in an 

 envelope, and from the adult in not having perfect wings. Insects are thus 

 rtubject to two principal kinds of metamorphosis, whence the latter have 

 l)een named Ilmnomorpha^ and the former Heteromorpha. The metamor- 

 phosis of the Lejyidoptera^ Coleoptera^ Ilymenoptera^ and Diptera^ is 

 heteromorphic ; whilst that of the Ortlioptera and llonipttera is liomo- 

 morphic. 



Heteromorphic larvai are more or less cylindrical, with or without feet, 

 and a distinct head. They have generally thirteen segments, each of which 

 has been provided with a name by Newman, as follows, commencing with 

 the head: \^ caput', 2, j'^roMorö'.T;/ 2>^nnesothorax', ■^^ metathorax ', b^ pro- 

 podeon; (S^podeon', 7, metapodeon ; 8, octoonj 1), ennaton', 10, decaton; 

 11, j^roteluni; 12, pa7'atelum,' Id, telic?)i. 



The head of larvjE is in some cases not different from the other segments, 

 being equally soft, and without antennae, eyes, or jaws. A larva of this 

 kind (the feet being also absent) is popularly termed a maggot. The cater- 

 pillars, which have a more perfect (organization, have a corneous head 

 generally bearing the various organs apparent in the perfect insect or imago. 

 The antennae of larvfe have a simple structure, and but few articulations, 

 i!ven in those cases where the adult has them complicated and very long. 



Of the two kinds of eijes found in adult insects, compound and simple, the 

 latter, named fifemmata, are alone present in the larva^, 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 larvai of some Coleoptera have an analogous 

 organ at the posterior extremity. 



The sides of terrestrial larva» generally show the spiracles, whicli 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 larva? there are lateral gills, and in others breathing is accomplished 

 through the posterior extremity. 



The larva state is tliat 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 larvae. 

 Cicada septendechn (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, the dilfereiit stages of the genus Ptialangopsis can 

 hardly be determined, but we have observed that certain spines upon the 

 legs appear only in the last stage, thus indicating the adult. 

 338 



