THE SPOROZOA 



255 



The reproductive phases of the majority of Haemosporidia are 

 very imperfectly known, and in most cases the statements that 

 have been made require revision, or at all events reinterpretation, 

 in the light of recent discoveries. As regards the non-sexual 

 cycle, it is interesting to note that in many forms the schizogony 

 takes the most primitive form of multiplication by simple binary 

 fission. This is the case in the species of the genus Piroplasma, 

 where the pear-shaped trophozoite divides within the blood- 

 corpuscle into two twin bodies, from which circumstance the type- 

 species of the genus has received the specific designation bigeminum. 

 Each of the daughter trophozoites may in its turn divide again. 

 A similar binary fission occurs also in the species Haemogregarina 

 Ugemina, recently discovered by Laveran and Mesnil [79] in two 

 species of blennies. In the majority of Haemosporidia, however, 

 the schizont divides up simultaneously into a number of merozoites, 



Haemogregarina Hgemina, Laveran, from the blood of blennies. a, the form of the parasite 

 found free in the blood plasma. 6, parasite within a blood -corpuscle, preparing for divi- 

 sion ; the nucleus has already divided, c, the parasite has divided into two rounded corpuscles, 

 which assume the form of the free parasite, as seen in il, c, and /. A r , nucleus of the blood- 

 corpuscle ; n, nucleus of the parasite. The outline of the blood - corpuscle is indicated by a 

 thick black line. (After Laveran.) Magnified about 1800 diameters. 



which may be disposed in various ways. Besides the " rosette " 

 or " daisy " pattern described above for Laverania, they may be 

 arranged in the form of a " barrel," with the residual protoplasm 

 at one extremity, as in the Eimerian phases of Coccidia, or they 

 may be implanted on each side of the residuum, or in other ways. 

 Sometimes the arrangement may vary in the same species, as in 

 Lankesterella (Drepanulium) ranarum, where the merozoites may be 

 formed on one side only of the schizont, or may have the radiate, 

 daisy-like arrangement. The schizogony is usually intracellular, 

 and takes place within a blood-corpuscle, or in the cells of certain 

 internal organs, more particularly the spleen, liver, and bone 

 marrow. The schizont often becomes surrounded by a membrane, 

 forming a so-called cytocyst (Fig. 73). Sometimes, however, the 

 sporulation may be free, i.e. extracellular, especially in the spleen- 

 pulp. 



In many Haemosporidia of cold-blooded animals there appears 

 to be a well-marked dimorphism in the schizonts, as well as in the 



