INSECTS IN GENERAL. 



THE METAMORPHOSES OF INSECTS. 



Nothing in the history of insects is more remarkable than the striking 

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

 development. Whilst other animals progress from infancy to maturity, 

 simply by a process of growth, and by such gradual and imperceptible 

 changes only as their growth necessitates, many insects assume totally 

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

 never be recognized as the same individuals, if this development had 

 not been actually traced from one stage to another. These changes are 

 called the metamorplioses or transformations of insects. All insects, in 

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

 larva, or caterpillar state; the imjya, or chrysalis state ; and the imago, 

 or perfect and winged state. The metamorphoses of insects are of two 

 principal kinds, complete and incomplete. 



In the complete metamorphosis the larva bears no resemblance to the 

 imago, and the insect, in the intermediate or pupa state, is motionless, 

 and takes no food. This kind of metamorphosis presents two principal 

 varieties. In some (Lepidoptera and many Diptera), the legs and wings 

 are completely inclosed in the i>upa case. In others (Coleoptera, Hy- 

 menoptera, and some others), the legs of the pupa, though useless, are 

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

 some (the noctural Lepidoptera, and many Hymenoptera), the pupa 

 is inclosed in a separate covering or cocoon, whereas the majority of in- 

 sects have no such .covering. Pupoe thus inclosed are called folliculate. 

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

 plied to the pupa} of the diurnal Lepidoi^tera, because the pupai of some 

 butterflies are ornamented with golden spots. 



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

 larval skin, but in many of the two-winged flies, (Muscidic, Syriphida?, 

 etc.) the larval skin becomes contracted 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. Pupaj thus in- 

 closed are called coarctate, 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 ^gg. 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 stay? is dis- 

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

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

 or bugs pro[)er, and all the Orthoptera, or crickets, grasshoppers and 

 cockroaches, exhibit this imperfect kind of metamorphosis. 



