ANIMAL PARASITES 



297 



is the pig. In the alimentary canal of the pig the young 

 tapeworm develops, to bore its way later through the 

 walls of the canal and become imbedded in the muscles. 

 There it lies until the diseased flesh containing it is eaten 

 (without being perfectly cooked), and it thus finds its way 

 into the alimentary canal and thence into the intestine of 

 man. It now continues to develop until it becomes full 

 grown . 



Parasitic insects Among the insects many live as 



parasites during their immature or larval life, but as adults 

 are free and independent creatures. From the chrysalid 

 of a butterfly or moth there will often come not a butter- 



FiG. 234. — Larva of a sphinx-moth, with cocoons of a parasitic ichneumon 

 fly. (From specimen.) 



fly but numerous tiny four-winged gnats, called ichneumon 

 flies. This is what happened. When the butterfly 

 caterpillar was crawling about a female ichneumon darted 

 down on it, and with her sharp ovipositor either laid 

 several eggs beneath its skin or glued them to its outer 

 surface. These eggs hatched in two or three da}'s as 

 tiny white ichneumon grubs, which immediately burrowed 

 deep into the caterpillar and lay there feeding on the 

 blood and tissues of its body. But the caterpillar went 

 on eating and finally changed into a chrysalid, with the 

 ichneumon grubs still inside. Soon the grubs, having 

 eaten up most of the body of the developing butterfly 

 and thus killed it, changed into tiny pupse, and later into 



