SCHIZOGONY AND SPOROGONY 67 



and any other material to be discarded, such as pigment, is known as the 

 residual body. It takes no further part in the life of the organism, and 

 after separation of the merozoites quickly disintegrates (Fig. 39, 6). 



Amongst the Sporozoa, after syngamy has taken place, the zygote 

 divides by a process which is essentially the same as schizogony. This is 

 termed sporogony, and it gives rise to sporozoites, which differ in size and 

 shape from the merozoites. The sporozoites arise from the multinucleate 

 zygote, which may have increased considerably in size and is called the 

 sporont, by a budding process which is very similar to that by which the 

 merozoites are formed (Fig. 455). The term " sporogony " is generally 

 extended to include the whole phase of the developmental cycle from the 

 beginning of the production of gametes or gametocytes to the formation 

 of sporozoites from the sporont after syngamy has taken place. To 

 distinguish the other phase of development during which schizogony 

 occurs repeatedly without the intervention of a sexual process, it has 

 been termed agamogony, and the various stages (merozoites and schizonts) 

 agamonts. The growing agamont is often termed a trophozoite. 



During the formation of merozoites and sporozoites it not infrequently 

 happens that the number of nuclei present is so large that the surface 

 of the cytoplasm is insufficient to accommodate them all. By a process 

 of vacuolation of the cytoplasm the available surface is increased. The 

 vacuoles may open into one another, so that the cytoplasm is reduced to 

 the condition of a coarse network. In this way the available surface 

 upon which nuclei can take up their position is increased, so that the 

 merozoites or sporozoites can be budded off in the usual manner. A 

 typical instance of this increase in surface occurs during the formation of 

 sporozoites in the oocysts of the malarial parasites on the stomach of 

 mosquitoes, as also during schizogony of Aggregata eherthi and other 

 Sporozoa (Figs. 377 and 391). 



A method of schizogony which occurs amongst the piroplasmata must 

 be mentioned. In these parasites the number of daughter forms produced 

 are two or four, which are described as arising from the parent by a budding 

 process, in contrast to the supposed segmentation of the schizont of the 

 malarial parasites. As already explained, the merozoites of malarial 

 parasites are not produced from the parent by a sudden splitting of the 

 body between the nuclei, but by the formation of buds from its surface, 

 as occurs generally amongst the Sporozoa. The piroplasmata are no 

 exception to this rule. In some species {Babesia canis) the buds are 

 usually two in number, but may be four (Fig. 417). In others (B. equi) 

 there are usually four buds, as in Plasmodium minasense (Fig. 416 and 

 Plate XVII., 6-15, p. 982). The bud commences as a small cytoplasmic 

 elevation on the surface of a rounded parasite. It gradually increases in 



