64 



VETERINAKY PATHOLOGY. 



";l' — SarcoCAwtis IMiewIieri. Drawing made with f^amfra liK'ida. 

 <'i"nss S'Ction sarcocyst. musclr <ill '.nclosing sarcucyst ruptured. 

 <_'ri)ss section of in-art muscio cell. 

 Fibrous connective tissue 



than the closely related nonparasitic animals. The simplicity of 

 parasites is a result of adaptation to environments m which es- 

 sential structures of the nonparasitic tvpe, useless to the para- 

 sitic tyjie. atriiphv because of disuse. The parasitic helminthes 

 are of the simplest structure, their nervous, dig"estive and respi- 

 ratiirv systems being \'erv rudimentary. 



Their food is obtained from their host. Some animal para- 

 sites, as the tapeworm (Taenia) absorb dis^ested food stuff from 

 the intestine of their host, others subsist upon the host's blood, 

 (Uncinaria), and still others consume tissue juices and lyinph, 

 (Trichina spiralis). The reproduction of helminthes is accom- 



