ioo PHYLUM PROTOZOA THE SIMPLEST ANIMALS. 



bent spindle (falciform), and seems next door to being 

 flagellate. It bores into a mother sperm cell, and from this 

 it afterwards passes as an adult into the cavity of the 

 seminal vesicles. In some allied Sporozoa the young form 

 is first flagellate, and then amoeboid, before it becomes the 

 sluggish adult. Intracellular parasitism and copious food 

 naturally act as checks to activity. 



The species of Monocystis occur chiefly in "Worms" and 



sp.c 



FIG. 44. Life history of Monocystis. After Biitschli. 



1. Gregarine lying within a sperm mother cell of earthworm. 



2. Conjugation of two Gregarines within a cyst. 



3. Numerous spore-cases (sp.c., pseudonavicellae) within a cyst. 



4. A spore-case with eight spores (.?/.) and a residual core (rb.). 



Tunicates ; none are known in Arthropods, Molluscs, or 

 Vertebrates. 



Seventh Type of Protozoa COCCIDIUM SCHUBERGI. 



Coccidia are intracellular parasitic Sporozoa, attacking 

 mainly the epithelial cells of the gut or associated organs. 

 They are found chiefly in insects, myriopods, molluscs, and 

 vertebrates. 



Coccidiiim schubergi infests the intestinal epithelium of 

 the centipede Lithobiiis forficatus. The adult is a minute 

 oval or spherical cell with a nucleus. It lives a quiescent 

 life within the host cell, growing and absorbing nourishment 

 until the resources of the cell are exhausted. 



Life history.- -The adult coccidium enters the host cell 

 as a minute sickle-shaped body, pointed at the anterior end, 

 and more blunt posteriorly. This is the sporozoite stage of 

 the life history ; it is liberated from a cyst (oocyst) when the 

 latter is swallowed by the centipede in its food. When 



