MOULTING OF THE CATERPILLAR 645 



the two hours immediately preceding the change to the pupa, and 

 increases in frequency as that period approaches. He thus describes 

 the mode of moulting the larval skin : " When the period has arrived, 

 the skin bursts along the dorsal part of the 3d segment, or meso- 

 thorax, and is extended along the 2d and 4th, while the coverings 

 of the head separate into three pieces. The insect then exerts 

 itself to the utmost to extend the fissure along the segment of the 

 abdomen, and, in the meantime, pressing its body through the open- 

 ing, gradually withdraws its antennae and legs, while the skin, by 

 successive contortions of the abdomen, is slipped backwards, and 

 forced towards the extremity of the body, just as a person would 

 slip off his glove or his stocking. The efforts of the insect to get 

 entirely rid of it are then very great; it twirls itself in every 

 direction in order to burst the skin, and, when it has exerted itself 

 in this manner for some time, twirls itself swiftly, first in one 

 direction, then in the opposite, until at last the skin is broken 

 through and falls to the ground, or is forced to some distance from 

 it. The new pupa then hangs for a few seconds at rest, but its 

 change is not yet complete. The legs and antennae, which when 

 withdrawn from the old skin were disposed along the under surface 

 of the body, are yet separate, and do not adhere together as they do 

 a short time afterwards. The wings are also separate and very 

 small. In a few seconds the pupa makes several slow, but powerful, 

 respiratory efforts; during which the abdominal segments become 

 more contracted along their under surface, and the wings are much 

 enlarged and extended along the lateral inferior surface of the 

 body, while a very transparent fluid, which facilitated the slipping 

 off of the skin, is now diffused among the limbs, and when the pupa 

 becomes quiet dries, and unites the whole into one compact covering." 

 The changes in the head and mouth-parts. --The changes of form 

 from the active mandibulate caterpillar to the quiescent pupa, and 

 then to the adult butterfly, are, as we have seen, in direct adaptation 

 to their changed habits and surroundings, and they differ greatly in 

 details in insects of different orders. In many Lepidoptera and 

 certain Diptera the pupa and imago are Avithout the mandibles of the 

 larva, and, instead, the 1st maxillae in the former order, and the 2d 

 maxillae in the latter, are highly developed and specialized. The 

 changes in the shape of the head, with the antennae, the latter rudi- 

 mentary in the larva? of the two orders named, are noteworthy, and 

 will be referred to under those orders. The same may be said of 

 the thorax with the legs and wings, and the abdomen with the ovi- 

 positor. Every part of the body undergoes a profound change, though 



