84 SUPPLEMENT ON 



form advance out of their shell by the assistance of the stiff 

 points with which the segments of their bodies are furnished. 



The fifth and last mode of metamorphosis is exhibited by 

 the pupa of the majority of two-winged insects. This is the 

 sort of nymph which Fabricius terms coarcta. The larvae 

 of these insects, which are very improperly called the worms 

 of flies, are indeed devoid of feet. They move, however, by 

 the aid of some peculiar organs, and with more or less agi- 

 lity. Most of them are developed in very humid situations, or 

 substances, and even in liquids. They change their skin several 

 times, but at their last moulting they totally lose their primi- 

 tive forms. Their body grows shorter, contracts itself so as to 

 present the appearance of an egg-shell, or elongated ball, the 

 envelope of which, at first soft and whitish, afterwards grows 

 hard and brown, leaving externally to be distinguished no 

 trace, no lineament, no appearance of any kind of the insect 

 which it contains. It is, in fact, a sort of corneous shell in- 

 dependent of the animal which it protects. When it is 

 opened, an insect is found in the nymph state, analogous to 

 that of the coleoptera in the contraction of its members. 

 When this pupa has acquired a sufficient degree of consist- 

 ence, it begins to work upon the walls of its prison, which 

 tear constantly and circularly so as to allow the body of the 

 insect to be disclosed, which comes forth quite moist, and the 

 wings but little developed. These, however, soon become 

 sufficiently extended to sustain the insect in the atmospheric 

 air, in which its new mode of locomotion is to be exerted. 



Such are the principal metamorphoses of insects. There 

 are some which participate in many of the modes of transfor- 

 mation we have now described. The study of this period 

 of insects is certainly one of the most curious and interesting 

 that can engage the attention of the naturalist. In some 

 species in particular, the change of the nymph into the per- 

 fect insect takes place with the most extreme rapidity, and 



