124 



PHYLUM PROTOZOA^ — THE SIMPLEST ANIMALS 



nucleus divides up, and eight elongated spores are formed 

 round a residual core. The spore-case now takes its typical 

 shape and is known as a pseudonavicella. The spores are 

 considerably larger than those of Gregarina. Eventually, in 

 the alimentary canal of another earthworm the cyst bursts, 

 the spore-cases are extruded, the spores emerge from their 

 firm chitinoid cases. The young spore (sporozoite) is like 

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

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



Fig. 56. — Life-history of Gregarina. — After Butschli. 



1. Young forms {a, b, c) emerging from intestinal cells (i.e.) ; i.n., 



nucleus of intestinal cell. 



2. Two forms conjugating (0. blattarum). 



3. Spore formation within a cyst. 



4. .\dult with deciduous head-cap (c.c), and a cuticular partition 



dividing the cell into an anterior part (A ) and a posterior part 

 (B) ; n., the nucleus. 



5. A spore-case (sp.c). 



it afterwards passes as an adult into the cavity of the 

 seminal vesicles. Intracellular parasitism and copious food 

 naturally act as checks to activity, and the adult is sluggish. 



The allies of Monocystis occur chiefly in " Worms," 

 Tunicates, and x\rthropods ; none are known in Vertebrates. 



Along with Monocystis we take Gregarina, a type of 

 Sporozoa in which the cell is divided into two regions by a 

 partition. Various species occur in the intestine of the 

 lobster, cockroach, and other Arthropods. When young 

 they are intracellular parasites, but later they become free in 



