PUPATION OF LEPIDOPTERA. 25 



works itself through the rent by alternately dilating and contracting the rings of its body, and 

 working the larva skin backwards towards the tail. How the tail of the apparently helpless pupa 

 could be withdrawn from the old skin, and fixed in the silk button without the pupa itself falling, long 

 remained unexplained, and it was always supposed that the pupa seized the old larva skin between two 

 of the segments of its body, as with a pair of pincers, and thus worked itself upwards. But according 

 to recent observations of Dr. Osborne this is not so, but the pupa remains connected with the old 

 larva skin by " a membrane extending from the lining of the latter to the anterior horns of the two 

 lateral ridges bounding the anal area of the chrysalis." Some writers regard this membrane as formed 

 of the lining of the tracheae, which, as well as that of the intestinal canal, is thrown off with the cast 

 skin of the larva. Nor is the membrane the only support of the pupa, for the interior of the larva 

 skin and the surface of the pupa are damp, if not actually wet, at this stage, and the pupa is, there- 

 fore, in part at least, upheld by capillary attraction. The chrysalis then stretches up its tail towards 

 the button of silk, and by a series of violent efforts succeeds in reaching it, and in fixing itself by the 

 small hooks with which its tail is provided. It then whirls itself round several times, first in one 

 direction and then in the other, in order to secure its hold, and to fix the hooks as firmly as possible. 

 During this process the connection between the pupa and the cast-off skin of the larva is almost 

 always severed, and the latter falls to the ground. 



The pupation of the larvse of those Butterflies in which the pupa is attached to a stem, horizontally 

 or vertically, by the tail and by a girth of silk round the body, is effected in a very similar manner. 

 Some larvae, like those of the Pierince, are sufficiently flexible to attach a thread on one side of their 

 body, and then carry it over, and fasten it on the other side, repeating the operation as often 

 as necessary ; but in the case of the Lyccenidce the girth is spun first, and the larva slips its head 

 under afterwards. The Papilionince, on the other hand, spin their girth, holding the separate threads 

 in their claws until the girth is strong enough, when they slip them over their heads. This arrange- 

 ment is necessary on account of the great risk of entangling the numerous threads of which the 

 girth is composed. 



The larvae of many Moths construct a hollow ball of silk, called a cocoon, in which to pass the 

 pupa state, and it is from the cocoon of the Silkworm and other Moths that the silk of commerce is 

 derived. Some cocoons, like that of the Silkworm are entirely closed, while others, like that of the 

 Emperor Moth, are partially open at one end, being constructed somewhat after the manner of a 

 weir, so that while they form no impediment to the egress of the enclosed Moth, an enemy cannot 

 force its way in from the outside. The larvae of many Sphinges, <fcc., construct a cell in the ground, 

 lined with agglutinated earth and silk, and those of the Goat Moth and other internal feeders, 

 form their cocoons in the solid wood of trees, forming a tunnel leading up to, but not breaking 

 through, a partition opening upon the outer air. Some cocoons, like those of various Notodontidce, 

 are attached to the bark of trees, which they closely resemble, and are as hard as wood. Many 

 larvae which spin cocoons construct them in the autumn, and lie dormant till the following spring, 

 without assuming the pupa state till then. 



Cocoons are not always made of silk alone. It has already been mentioned that cells 

 made underground are partially formed of agglutinated earth. Hairy caterpillars often weave 

 their hairs into their cocoons, and others employ fragments of leaves, moss, lichen, or comminuted 

 wood. Many larvae, however, scarcely construct any cocoon, forming their pupae between leaves or even 

 on the surface of the ground, often without any preparation. Many of the large foreign Saturniidce 

 make their cocoons within a leaf, which they connect with the branch by a strong silken band several 

 inches long, running along the leaf-stalk, so that even if the stalk becomes detached from the 

 branch, the leaf cannot possibly fall to the ground. 



It is believed that the object of cocoons is not warmth, but protection ; for the temperature 

 within does not exceed that of the surrounding earth or air. Protection, however, is not their only use ; 

 for the efforts which the insect makes to escape, and the pressure which the cocoon' exerts upon it, are 

 so essential to its development, that pupae prematurely removed from their cocoons often produce only 

 crippled specimens. 



The pupa is generally of a brown colour, but those of Butterflies, which are exposed to the sun 

 and air, are sometimes green, yellow, or metallic. The rudiments of the perfect insect, which can 

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