130 SOME MINUTE ANIMAL PARASITES 



two practically identical masses, so arranged that 

 the broad part of the one is adjacent to the narrow 

 part of the other. The two vermiform organisms 

 thus produced in each spore are the two sporozoites 

 (Figs. 28, T ; 29, F) similar to those with which the 

 life-cycle began. 



When a fresh preparation containing many oocysts 

 is examined, variations as to size and shape of the 

 cysts as well as in the arrangement of the contents, 

 will be seen. This is only to be expected, seeing 

 that size and shape are largely dependent on the 

 quantity of food available and the amount of space 

 at the disposal of the parasite. At the commence- 

 ment of cyst formation, when the number of cysts is 

 relatively few, there is an abundance of food, and 

 the parasites do not suffer from overcrowding. As 

 a result, the oocysts are well formed and large. 

 When the same host cell is invaded by several 

 merozoites, together or successively (and this often 

 happens), and when at the same time the adjacent 

 cells are also highly parasitized, then there is restric- 

 tion both m the food-supply and in the space. 

 Squarish or egg-shaped oocysts of smaller size are 

 often produced under such conditions. Further, 

 when sections are examined, the above reflexes of 

 space conditions and nourishment available are seen. 

 Thus, when the number of trophozoites in any area is 

 unduly large, the schizonts produced do not grow to 

 the normal size and produce eight to fourteen or 

 even twenty merozoites, but remain small, and 

 commonly form about four merozoites. Thus it is 

 seen that two methods of maintaining the constancy 



