538 



BIOLOGY OF THE PROTOZOA 



species which pass their trophic stages in the digestive tract of 

 Crustacea and their sexual stages in mussels. Porospora gigantea 

 grows to an enormous size (up to 1(> mm.) in the lobster (Homarus 

 sp.) where it apparently lives for a long period. Ultimately, and 

 either in association or individually, it becomes spherical and forms 

 a cyst-like ball with a diameter of 3 to 4 mm. The ball then divides 

 into many gametocytes, each with a diameter of from 5 to 8 /x, and 





Fig. 215.— Gametes of Gregarines and Coccidia. A, male and female gametes of 

 Stylorhynchus longicollis; B, Monocystis sp.; C, spermatozoid of Echinomera hispida, 

 to the left the two gametes of Pterocephalus nobilis; D, gametes of Urospora lagidis; 

 E, of Gregarina ovata; F, of Schaudinnella henleae; and G, of Eimeria schubergi. (From 

 Shellack after Leger, Cuenot, Brasil, Schnitzler and Schaudinn.) 



each gametocyte forms gametes which are arranged radially about 

 a central residual body. The gametes are very small (3ju long by 

 1 ix in diameter) and pass out with the feces into the water with 

 which they enter the digestive tract of the mussel (Mytilus edulis) 

 where they unite to form zygotes. Each zygote forms a single 

 sporozoite which is liberated in the gut of the lobster. 



The Schizogregarinida are more complicated through the intro- 

 duction of an asexual reproductive phase in the life history leading 



