428 BIOLOGY OF THE PROTOZOA 



Well-marked anisogamy is found in Pterocephalis nobilis (Duboscq 

 and Leger) and in SchaudinurUa henleoB (Nusbaum), but in general, 

 difi'erences in gametes are much less pronounced than in the Coccid- 

 iomorpha (Fig. 183). 



The sporoblasts in different species vary widely in form and in 

 sculpturing. The capsule is usually double consisting of an inner 

 (endospore) and an outer (exospore) capsule, the latter sometimes 

 provided with short spines (Ar(inihospora) or long filaments (Cerato- 

 spora). The typical number of sporozoites in a sporoblast is eight 

 but this is not invariable. They are liberated by action of gastric 

 juices and emerge through preformed openings or by separation of 

 the two valves of the sporoblast. They creep out of the endospore 

 and make their way to epithelial cells within which the first stages 

 of their development occur. 



Order 1. Eugregarinida, Doflein Emend. 



The great majority of known gregarines belong to this Order, the 

 agamous individuals living for long periods in the host before uniting 

 in couples to form isogamous or anisogamous gametes. Division 

 or asexual reproduction of any kind is unknown. Only exceptionally 

 are more, or less, than eight sporozoites formed in each sporoblast. 

 They are monocystid (single chambered) or polycystid in structure 

 the former grouped in the Sub-order Acephalina, the latter in the 

 Cephalina. 



Sub-order 1. Acephalina, Koelliker (Monocystidea, Stein). 



1. Genus Monocystls, Stein (1848). The troj^hozoites are often highly 



contractile owing to the peristalsis brought about by the contrac- 

 tions of ectoplasmic myonemes. Spores boat-shaped and octozoic. 

 Many species from worms and entomostraca, a typical species, 

 M. agilis may be found almost invariably in the seminal reservoirs 

 of the common earthworm, and excellent stages in sporulation and 

 fertilization may be easily obtained. 



2. Genus Zygocystis, Stein (1848). The trophozoites are usually found in 



pairs or groups of three. Typical species, Z. cometa, Stein, found in 

 the seminal vesicles and body cavity of the earthworm Lumbricus 

 agricola. 



3. Genus Zygosoma, Labbe (1899). The trophozoite has typical and 



characteristic finger-like processes and is usually found in couples. 

 Sporulation unknowai. Typical species, Z. gibbosum, Greeff (1880), 

 in the gut of Echiurus pallassii. 



4. Genus Pterospora, Racovitza and Labbe (1896). The pyriform tropho- 



zoites are always associated in couples. The spores have dissimilar 

 poles and the epispore is drawn out into lateral processes. One 

 species, P. maldaneorum, R. and L., from the coelomic cavity of 

 maldanid worms. 



5. Genus Cystobia, Mingazzini (1891). The trophozoites are large and 



irregular in form and usually have two nuclei due to the early fusion 

 of two individuals. The spores are heteropolar, and the epispore is 



