OTHER NON-COLONIAL PROTOZOA 



79 



cysts containing individuals of the Genus Monocystis, a sporozoan 

 which lives in the seminal vesicles of the earthworm, can be studied 

 (Fig. 39). Here the encysted stages are abundant in infected speci- 



FiG. 39. — ^Life-cycle of the gregarine, Monocystis. A, spore consisting of a 

 spore-case enclosing eight sporozoites. B, transverse section of same. C and 

 D, hberated sporozoites. E, sporozoite after entering multicellular sperm- 

 sphere of earthworm. F, growth in sperm-sphere to form a trophozoite which 

 is later surrounded (G) by the remains of the sperm-sphere consisting of a 

 thin envelope to which the tails of the degenerate spermatozoa adhere. H, 

 two trophozoites that have become free of the degenerate sperm-spheres and 

 united as gametocytes. /, encystment of gametocytes. J, reproduction by 

 sporulation, or multiple division of the nucleus followed by cytosomal con- 

 strictions, to form isogametes. K, reproduction by union of the isogametes 

 to form zygotes; the residual cytoplasm of the gametocytes is in the center 

 of the cyst. L, cyst containing many sporozoites, formed by secretion of a 

 spindle-shaped spore case around each zygote which undergoes sporulation 

 to form eight sporozoites; these eventually become arranged as in A and B, 

 in which state they are transferred to another earthworm. 



(Drawn by Wiley Crawford.) 



mens, while the active stages are less numerous. Take a bit of the 

 seminal vesicle from a fresh earthworm, and tease it out in 0.9% salt 

 (sodium chloride) solution on a slide. Add a cover glass and look for 

 spherical bodies, containing two hemispherical cells or many smaller 



