35* 



Descriptive Zoology. 



of an inch in length. It is sometimes called the " pork- 

 worm." As is well known, this parasite is obtained by 

 eating raw or partially raw pork, and there is no danger 

 when the flesh is thoroughly cooked. If they gain access 

 to the intestine of the pig, the females bring forth alive a 



FIG. 199. TRICHINA ENCYSTED IN HUMAN MUSCLE. 



Highly magnified. From Packard's Zoology. 



large number of young. These bore their way outward 

 into the muscles and there inclose themselves in a sac or 

 capsule, where they may remain an indefinite time. If 

 this pork, uncooked, is eaten by man, the capsule is di- 

 gested and the larvae are set free. The young soon bore 

 through into the muscles and each worm gets into a muscle 

 cell and coils up in a case or "cyst," which it forms for 

 itself. 



The Guinea Worm. In the East Indies occurs another 

 parasite, the guinea worm. It is sometimes found two 

 feet long, embedded in the connective tissue under the 

 human skin. It is supposed that the eggs or larvae are 

 introduced in drinking water. 



BRANCH TROCHELMINTHES. 



THE ROTIFERS. 



The Wheel Animalcule. The word "Rotifer" means 

 wheel bearer, from the two circular disks at the anterior 

 end, around the borders of which are circles of cilia whose 



