



DEVELOPMENT 



upae are supported by a silken girdle (Fig. 29), and nymphalid chrysa- 

 lides hang freely suspended by the tail (Fig. 215). 



Cocoon-Spinning. The caterpillar of Telea polyphemus " feels with 

 its head in all directions, to discover any leaves to which to attach the 

 fibres that are to give form to the cocoon. If it finds the place suitable, 

 it begins to wind a layer of silk around a twig, then a fibre is attached to 

 a leaf near by, and by many times doubling this fibre and making it 

 shorter every time, the leaf is made to approach the twig -at the distance 

 necessary to build the cocoon; two or three leaves are disposed like this 

 one and then the fibres are spread between them in all directions, and 

 soon the ovoid form of the cocoon distinctly appears. This seems to 



FIG. 218. Cocoon of Samia cecropia, cut open to show the two silken layers and the 

 enclosed pupa. Natural size. 



be the most difficult feat for the worm to accomplish, as after this the 

 work is simply mechanical, the cocoon being made of regular layers 

 of silk united by a gummy substance. The silk is distributed in 

 zigzag lines about one-eighth of an inch long. When the cocoon is 

 made, the worm will have moved his head to and fro, in order to distrib- 

 ute the silk, about two hundred and fifty-four thousand times. .After 

 about half a day's work, the cocoon is so far completed that the worm 

 can hardly be distinguished through the fine texture of the wall; then 

 a gummy resinous substance, sometimes of a light brown color, is spread 

 over all the inside of the cocoon. The larva continues to work for four 

 or five days, hardly taking a few minutes of rest, and finally another 

 coating is spun in the interior, when the cocoon is all finished and com- 

 pletely air tight. The fibre diminishes in thickness as the completion 

 of the cocoon advances, so that the last internal coating is not half so 

 thick and so strong as the outside ones." (Trouvelot.) 



