PARASITISM 339 



Class Sporozoa. These form a large group of 

 mtracellular parasites, some, as Coccidia, being 

 parasites of epithelial cells, others, like Plasmo- 

 dium, blood parasites, and still others, like the 

 Sarcocystis, muscle cell parasites. 



Phylum Porifera. There seem to be no parasitic 

 forms in this phylum. 



Phylum Ccelenterata. This furnishes very few para- 

 sitic representatives, none of which affects man. 



Class Hydrozoa. The Polypodium hydriforme 



at one stage of its life cycle is parasitic upon 



the immature eggs of the sturgeon. Cunina is 



parasitic in medusae. 



Class Scyphozoa. Probably has no parasitic 



representatives. 



Class Actinozoa Edwardsia is parasitic in 



Ctenophora; Pemmatodiscus on Rhizostoma. 



Class Ctenophora. Gastroides is parasitic in 



Salpa. 



Phylum Echinodermata. Probably has no parasitic 



representatives. 



Phylum Platyhelminthes. Among these worms are 



many parasitic individuals infesting man and lower 



animals. 



Class Trematoda. These worms are all para- 

 sitic. The best known are the liver flukes, 

 Fasciola hepaticum and Dicroccelium lanceo- 

 latum; the blood fluke Bilharzia hematobium 

 and the lung fluke Paragonimus westermanii. 

 All of these are parasites of man. In addi- 

 tion there are many others that infest the 

 lower animals. Some forms require but one 

 host, some an alternation of hosts. 

 Class Cestoda. These are the tape-worms, 

 all of which are parasitic. Of those infesting 

 man the best known are Tsenia saginata, 

 Tsenia solium, Dibothriocephalus latus, Hy- 

 menolepis nana, Dipylidium caninum, and 



