THE SPOROZOA 



191 



nucleus. Living as it does under rich nutrient conditions, the 

 cytoplasm of the cell at this stage is able to assimilate and store 

 up an abundance of food material to be used in later stages when 

 nutritive processes are in abeyance. Such powers of rapid assim- 

 ilation, and hence of rapid growth, are common in parasites during 

 favorable periods of their life cycles. 



Fig. 101. — Life cycle of the gregarine, monocystis. 



A, spore consisting of a spore case enclosing eight sporozoites. B, transverse section 

 of same. C and D, liberated sporozoites. E, sporozoite after entering multicellular sperm 

 sphere of earthworm. /' and G, growth in sperm sphere until the fully formed trophozoite 

 is formed surrounded by the degenerate remains of sperm sphere with flagella of sperma- 

 tozoa. H, two trophozoites that have become free of the degenerate sperm sphere and 

 united as gametocytes. I, encystmeut of gametocytes. J, division of nuclei and cyto- 

 plasm to form gametes. K, union of the gametes in isogamous conjugation to form 

 zygotes, residual cytoplasm of gametocytes in center of cyst. L, cyst containing many 

 sporozoites formed by secretion of a spindle-shaped spore case around each zygote, which 

 then divides to form eight sporozoites. These eventually become arranged as in A and B, 

 in which stage they are transferred to another host. (Drawn by Wiley Crawford.) 



Excretion of the waste products of dissimilation must occur, in 

 monocystis, by diffusion from the cell into the surrounding fluid of 

 the host. Hence, the parallel between a monocystis, living sur- 



