172 OTHER SPOROZOA 



this important purpose. At intervals the coccidians, instead 

 of multiplying in the usual manner, differentiate into sexual forms, 

 corresponding to eggs and sperms (Fig. 48G and H). One of the 

 spermlike individuals 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. 48 J): 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 - 



spora from British soldier Infection with coccidians has not often 



N"esence m of Sywo been observed in man but it is pos- 



sporocysts, each with four sibly more prevalent than is commonly 



sporozoites. X 1000. (After ,-, -, , /. f *.- : " 



Wenyon.) thought. A few cases of coccidian infec- 



tion of the human liver have been recorded 



and it has been generally assumed that the parasite was identical 

 with Eimeria stiedce of rabbits, but Dobell has pointed out that 

 there is no sound reason for this belief. Recently Wenyon has 

 reported the not uncommon occurrence of oocysts of two species 

 of coccidians in the faeces of British soldiers returning from Gal- 

 lipoli. The cysts of the commoner species, Isospora hominis, 

 contain a single mass of protoplasm when first passed, but in three 

 or four days they become fully developed and contain two sporo- 

 cysts, each with four sporozoites (Fig. 49). The cysts measure 

 12 M to 14 AI by 7 M to 9 M (about -^Vo by y^nr of an inch). The 

 cysts of the other species, Eimeria wenyoni, are fully developed 

 when passed, and possess four sporocysts with two sporozoites 

 each (Fig. 50) They measure 20 /z in diameter. Only four 

 cases of infection are known. A single case each of infection with 

 two other species have been recorded: E. oxy spora, with large 

 spherical cysts (36 ju in diameter) and straight sharp-pointed 

 spores, recorded by Dobell; and E. snijderi, with still larger 



