MONOCYSTIS 



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development, and amongst and within the sperm-mother- 

 cells Monocystis lives and passes through the various stages 

 of its life-history. The two commonest species are known 

 as M. agilis and M. magna. 



The encysted stage is the most easily recognised, and a 

 number of spherical cysts, varying between about \ and T ^ 



FIG. 74. Monocystis. 



A, Trophozoites in different stages of contraction. B, encysted gametocytes. 

 C,' division of gametocytes into gametes. D, conjugation of gametes to form 

 zygotes. E, Cyst enclosing ripe spores formed from the zygotes. F, single 

 spore, drawn to a larger scale, showing the (8) sporozoites in its interior. 

 G, group of developing sperm-cells of the earthworm, enclosing a sporozoite in the 

 centre. H, young trophozoites still surrounded with the tails of the degenerated 

 sperms, nu, nuclei. 



mm. in diameter, can usually be seen if a small piece of a 

 sperm-sac is examined under the microscope. When ripe 

 each cyst contains a large number of small spindle-shaped or 

 boat-shaped .spores (&). Before encystment Monocystis has 



