S INSECTS IN GENERAL. 



THE METAMORPHOSES OF INSECTS. 



-S ofhing in fke history of insects is more remarkable than the striking 

 ^changes of form which many of them undergo, in the course of their 

 ■deveiopraeat. Wfeilst other animals progress from infancy to maturity, 

 simply by a i)rocess of growth, and by such gradual and imperceptible 

 changes only as tSkmr growth necessitates, many insects assume totally 

 ' different forms in tfee course of their development, so that they could 

 inevefT be recognized as the same individuals, if this development had 

 mot been actually traoed from one stage to another. These changes are 

 icaXhd the ')roetamor2)homs or transformations of iusects. All insects, in 

 their growth, pass throcigh four stages, designated as the egg state ; the 

 larva, «or caterpillar state j the 2>i«J?rt, or chrysalis state; and the imago, 

 •or perfect and ^ss^nged trtate. The metamori)hoses of insects are of two 

 iprincipal kinds, complete -Mid incomplete. 



In (the complete metamorphosis the larva bears no resemblance to the 

 imago, «ffld the insect, ^in the intermediate or pupa state, is motionless, 

 and takes no food- This ikiud of metamorphosis presents two principal 

 ^varieties. In soi»ei(Lepidoptera and many Diptera), the legs and wings 

 .ar& completely inclosed in the pupa case. In others (Coleoptera, Hy- 

 menoptera, aa£ some -otkej's^, the legs of the pupa, though useless, are 

 :free, and the rudimental wings lie loosely upon the sides. Moreover, in 

 ■some (the noctKral L^pidoptera, and many Hymenoptera), the pupa 

 is inclosed in a separate cov>eriug or cocoon, whereas the majority of in- 

 sects have 110 such covering. Pupie thus inclosed are called folUculate. 

 The term chrysalis, from a Greek word meaning golden, is sometimes ap- 

 plied to the puftie of the diurnal Lepidoptera, because the pupae of some 

 butterflies are ornamented with golden spots. 



Most insects, in changing from the larva to the piapa state, cast off the 

 larval skin, but in many of the two-winged flies,' (Muscidte, Syriphidre., 

 ■etc.) the larval skin becomes (X)ntracted and hardened, assumes an oval 

 form and a brown color, and thus forms a compact and closely-fitting 

 case, in which the pupa proper is inclosed, but distinct. Puixe thus in- 

 closed are calkd marctate, and their cases are analogous to the cocoons 

 of the Lepidoptera, 



In the incomplete metamorphosis, the insect presents essentially the 

 same form, and is active in all its stages, after leaving the egg. The 

 pupa is distinguished from the larva by the presence of short rudimental 

 wings at the base of the abdomen, and the imago or adult state is dis- 

 tinguished by the fully grown wings and wing covers. It is ouly in this 

 last stage that insects are capable of propagation. All the Hemiptera, 

 or bugs proper, and all the Orthoptera, or crickets, grasshoppers and 

 cockroaches, exhibit this imperfect kind of metamorphosis. 



