i6 FIRST LESSONS IN ZOOLOGY 



and it is plain that the larva is making a silken case or 

 cocoon about itself. The spinning lasts about three days 

 and results in a thick, firm, white or yellowish (rarely 

 greenish) silken closed cocoon, within which the larva 

 moults. Cut one of the cocoons open a few days after 

 its making and there will be found within it the cast skin 

 of the larva and the pupa which appears after the final 

 larval moulting. In what habit does this pupa resemble 

 that of the mosquito .'' In what habit does it differ .■" The 

 pupal stage in the development of insects is a stage in 

 ■which the insect takes no food, is usually quiescent, and 

 is undergoing the final changes from -worm- or grub-like 

 larva to winged adult. The silkworm pupa lies quiescent 

 in its silken case for about two weeks, sometimes a little 

 longer, when the pupal cuticle splits, and one end of the 

 silken cocoon is dissolved by a fluid secreted by the insect 

 within. Through this opening out crawls the moth, 

 damp and crumpled-looking, with the wings all compressed 

 into short thick pads or sacs. But these slowly expand, 

 the scales and hairs covering the body dry, and soon the 

 robust fully developed white moth walks slowly about. 



Make a drawing of a net and cocoon just begun, show- 

 ing the larva inside at work spinning" ; also a drawing of 

 a completed cocoon ; and of a cocoon cut open showing 

 the mumm)'-likc pupa within. 



As the silkworm takes no food in the pupal stage (this 

 is true of the mosquito also) and as a great deal of devel- 

 opment goes on in this stage during which the ^\'ingless 

 larva is transformed into the very different winged imago, 

 it is plain that the pupa must live on food stored in the 

 body. It is for tliis reason that the larval mosquito, 

 the wriggler, and the larval silkworm moth, the silkworm, 

 devote themselves so steadily to eating ami eat more 

 than they need for their own use. The extra food eaten 

 is changed into fat, or is in some way stored in the body 



