172 OTHER SPOROZOA 



this important purpose. Probably stimulated by reactions 

 against them on the part of the host certain coccidians, instead 

 of multiplying in the usual manner, differentiate into sexual 

 forms, some transforming into large immobile egglike female 

 individuals or macrogametes (Fig. 48E and G), others dividing 

 into numerous very active flagellated spermlike male individuals 

 or microgametes (Fig. 48F and H). One of the spermlike in- 

 dividuals penetrates an egglike individual and fuses with it 

 (Fig. 481), in precisely the same manner as a spermatozoon 

 fertilizes an egg in higher animals. The fertilized individual 

 develops a thick resistant cyst wall and is then known as an 

 "oocyst" (Fig. 48J). The parasite is now ready to hazard the 

 dangers of an exit into the outside world, and is passed out with 

 the faeces. Eventually, sometimes within a few days, the con- 

 tents of the oocyst divide into several parts, each known as a 

 " sporocyst " (Fig. 48K, L and M). Each sporocyst in turn 

 develops within itself a number of " sporozoites " (Fig. 48N), 

 each capable of infecting a separate cell 

 in a new host. The oocysts with their 

 contained sporocysts and sporozoites can 

 exist in soil or dust for a long time, 

 awaiting an opportunity to enter a new 



FIG. 49. Oocyst of Iso- victim with food or water. 



from British soldier Infection with coccidians has not often 



been observed in man but it is pos- 

 sporocysts, each with four sibly more prevalent than is commonly 

 " I0 ' <After thought. A few cases have been re- 



ported of human infection with a coc- 

 cidian very similar to Eimeria stiedce, which infests the intestine 

 and liver of rabbits; some workers believe these cases to have 

 been caused by this very species, and that infection probably 

 resulted from eating infected livers of rabbits. Recently Wen- 

 yon has reported the not uncommon occurrence of oocysts of two 

 species of coccidians in the fasces of British soldiers returning 

 from Gallipoli. The cysts of the commoner species, of the genus 

 Isospora, contain a single mass of protoplasm when first passed, 

 but in three or four days they become fully developed and con- 

 tain two sporocysts, each with four sporozoites (Fig. 49). The 

 cysts of the other species, referred to the genus Eimeria, differ 

 in producing four sporocysts, each with two sporozoites (Fig. 



