134 ZOOLOGY. 



23erfect insect appears. In some cases the larva resembles the adult at all 

 times in most particulars ; and when, after successive inoultings, it becomes 

 a pu]3a, this is still much like the adult, and continues to eat and move 

 about, diflering 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 metamorj)liosis, whence the latter have 

 been named Homomorplia^ and the former Ileteromor^ha. The metamor- 

 phosis of the Lepidoptera^ Coleoptera^ Hymenoptera^ and Diptera^ is 

 heteromorphic ; Avhilst that of the Ortlioptera and Ileraiptera is homo- 

 morphic. 



Heteromorphic larva? are more or less cylindrical, witli or without feet, 

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

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

 tlie head: \^ caput; 'i^ protliorax ', Z^mesotTiorax; ^^ metathovax ; h^ pro- 

 fodeoii; ^^podeon; 7, metapodeon ', 8, octooh; 9, ennaton; 10, decaton; 

 11, protelmn', 12, parcdelum; 13, telum. 



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

 being equally soft, and without antenna?, 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 antenna? of larva? 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 simj^le, the 

 latter, named stemmata^ are alone present in the larvce, 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 larvae of some Coleoptera have an analogous 

 •organ at the posterior extremity. 



The sides of terrestrial larva? generally show the spiracles, which usually 

 amount to nine or ten upon each side. A\\ the segments, except the first, 

 or head, third, fourth, and last, are usually supplied with spiracles. In some 

 aquatic larvae there are lateral gills, and in others breathing is accomplished 

 through the posterior extremity. 



The larva 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 

 Melolonilta live a few weeks in the adult state, and three years as larv^. 

 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 w^ingless forms, as bed-bugs, and certain grasshoppers. 

 Amongst the latter, the different stages of the genus PJialangopsis can 

 hardly be determined, but V7q have observed that certain spines upon the 

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

 3^8 



