SCHIZOGONY AND SPOROGONY 69 



duces nearly always eight merozoites, and these vary little in size (Plate 

 XIII., p. 934). ^ijnilsiTly, Plasmodium vivax of benign tertian fever pro- 

 duces, as a rule, sixteen, but departures from this number are not uncom- 

 mon (Plate XII,, 16-18, p. 926). Amongst other Sporozoa, however, greater 

 variations occur, as will be described below. In some cases it has been 

 supposed that the schizogony was of two types- — the one giving rise to a 

 small number of large merozoites, and the other to a large number of 

 smaller ones (Fig. 39, 6 and 7). It was supposed that this represented 

 a sexual dimorphism, one line ending in gametocytes of the female sex, 

 and the other in gametocytes of the male sex. More careful study of such 

 cases has thrown doubt on these conclusions, and has tended to show that 

 every transition, both as regards numbers and size, occurs between the two 

 types. Thus, in the case of Adelina dimidiata, a coccidium of the centipede, 

 the merozoites produced by a schizont vary in number from four to 

 sixteen, as demonstrated by Schellack (1913). As a rule, when the number 

 is large the merozoites are small, and vice versa. In Hepatozoon canis 

 (Fig. 39) the number of merozoites produced may be only four, or it may 

 exceed a hundred. In this case it appears that with successive schizogony 

 the number of merozoites produced increases, while their size diminishes, 

 till finally there are formed a large number of small ones which enter the 

 leucocytes and become gametocytes. It has thus to be remembered that 

 in any individual species the merozoites produced at schizogony may vary 

 considerably, both in number and size. 



In the case of sporozoites which are produced from the zygote by a 

 process similar to schizogony, the number and size is much more constant. 

 Thus the zygotes of coccidia belonging to the genus Eimeria invariably 

 produce eight sporozoites which are contained in pairs in four sporocysts 

 (Fig. 337). In other cases, as, for instance, in the genera Barrouxia and 

 Aggregata, though the number of sporocysts produced by the zygotes of 

 any particular species may vary considerably, the number of sporozoites 

 in the sporocysts is constant (Fig. 376). On account of its uniformity 

 the type of sporogony is of greater value for purposes of identification 

 and classification than are the forms observed at schizogony. 



GEMMATION OR BUDDING.— By this method of reproduction is to 

 be understood one in which an organism, after its nucleus has divided, 

 instead of splitting into two equal or nearly equal parts, divides very 

 unequally, so that one daughter form is very much smaller than the other. 

 The condition is one of extreme unequal binary fission. It is usual to 

 regard the large form as a parent individual, and the small one as a daughter. 

 The process has been described as occurring in free-living amoebae, and the 

 unequal divisions seen in Tnjpanosoma lewisi, which has already been 

 referred to, may be regarded as an instance of gemmation (Fig. 197). It 



