68 MULTIPLICATION OF PROTOZOA 



size at the expense of the cytoplasm of the parent. It is difficult to 

 understand why an organism which is to produce only two daughter forms 

 should do so by a budding process instead of by a simple binary fission 

 into two parts. It seems possible that it is a condition which has evolved 

 from one in which a larger number of merozoites were originally produced, 

 as in typical schizogony. 



When a schizont is in process of producing merozoites or a sporont 

 sporozoites, the schizont or sporont may first divide into a number of 

 intermediate bodies which actually produce the merozoites or sporozoites. 

 In the case of the coccidium Caryotropha mesnili, when about sixteen 

 nuclei are present in the schizont, it divides into sixteen portions which 

 have been called cytomeres or agametoblasts (Fig. 375). The nuclei of 

 these undergo further divisions, and finally merozoites are budded from 

 their surfaces. A similar method of multiplication occurs in Klossiella 

 cobayce and other forms (Fig. 449). Similarly, during sporogony the zygote, 

 instead of dividing directly into sporozoites, may first produce a number 

 of sporoblasts, which give rise to the sporozoites. In the coccidia sporogony 

 takes place within the oocyst which has formed around the zygote, and 

 it frequently happens that the sporoblasts secrete around themselves 

 secondary cysts or sporocysts, within which the sporozoites are finally 

 produced (Fig. 337). 



Attention has already been called to the fact that occasionally, amongst 

 flagellates which normally multiply by binary fission, the rate of division 

 of the nuclei may exceed that of the cytoplasm during very rapid multi- 

 plication, so that stages are reached in which an abnormal number of 

 nuclei are present (Fig. 142). The excessive nuclear multiplication, 

 however, comes to an end, and the body divides repeatedly till a number 

 of normal uninucleate forms are produced. In some cases such multi- 

 nucleate stages occur normally in the developmental process. Thus, in 

 the course of the development of Trypanosoma lewisi in the flea, the 

 trypanosomes taken up from the rat enter the cells lining the stomach, 

 and there grow into large bodies which possess as many as sixteen nuclei, 

 kinetoplasts, and flagella (Fig. 200). The " sphere," as it is called, then 

 divides into a corresponding number of trypanosomes. Such a method 

 of multiplication is really one of delayed division of the cytoplasm, 

 and must be distinguished from true schizogony. It seems probable 

 that the final division of the " sphere " takes place by repeated binary 

 fissions. 



During the process of schizogony the merozoites produced by any 

 particular organism vary as regards size and numbers. In certain cases 

 the variations are at a minimum, as, for instance, amongst the human 

 malarial parasites. Plasmodium malaricB of quartan malarial fever pro- 



