THE AMERICAN SILK-WORMS 



267 



of two walls of silk, the outer one being thick and paper-like and 

 the inner one thin and fim; between these walls is a matting 

 of loose silk, showing that the insect knows how to make a home 

 that will protect it from winter weather. It is a clever buildrr 

 in another respect, since at one end of the cocoon it spins the silk 

 lengthwise instead of crosswise, thus making a valve through which 

 the moth can push as it issues in the spring. It is very interesting 

 to watch one of these caterpillars spin its cocoon. It first makes 

 a framework by stretching a few stamds of silk, which like all 

 other caterpillars, it spins from a gland opening in the lower lip; 

 it then makes a loose net-work on the supporting strands, and then 

 begins laying on the silk by weaving its head back and forth leaving 

 the sticky thread in the shape of connecting M's or figure 8's. 

 Very industriously does it work, and after a short time it is so 

 screened by the silk, that the rest of its perf onnance remains to us a 

 mystery. It is especially mj^sterious since the inner wall of the 

 cocoon encloses so small a cell that the caterpillar is obliged to 

 compress itself in order to fit within it. This achievement would 

 be something like that of a man who built aroimd himself a box 

 onl}' a few inches longer, wider and thicker than himself. After 

 the cocoon is entirely finished the caterpillar sheds its skin for 

 the last time and 

 changes to a pupa. 



The pupa. — Very 

 different indeed does 

 the pupa look from 

 the brilliant colored, 

 warty caterpillar. It 

 is compact and 

 brown, oval and 

 smooth with ability 

 to move but ver\' 

 little when dis- 

 turbed. The cases 

 which contain the 

 wings, which are 

 later to be the ob- 

 jects of our admira- 

 tion are now folded 

 down like a tight 

 cape, around the Cocoon oj cecropia. 



