750 MUlilEL JiOLERTSON. 



type and geuerally of long standing. It is obvious that only 

 by following the successive stages of the infection in a 

 previously clean tortoise can points like this be really con- 

 clusively determined. 



Interpretation of the Two Types of Schizogony. — 

 There are three views which might be put forward in explana- 

 tion of the facts : (1) That the schizogony in the lung with 

 the large merozoites gives rise to the female gametes, and the 

 schizogony in the blood-corpuscles to male gametes. This 

 view is, I think, inadmissible, as it is very unlikely that the 

 small male gametes should be produced in such small numbers, 

 namely six to eight to one parent individual, while the female 

 gametes are produced in large numbers — about seventy to 

 one parent individual. 



(2) The second, and I think more probable, explanation is 

 that the schizogony in the lung is the endogenous asexual 

 multiplication, and that certain of the merozoites thus formed 

 proceed in turn to form gametocytes by the schizogony in the 

 blood-stream. 



(3) A third quite plausible explanation is that the schizogony 

 in the lung is brought about by the newly injected parasite — 

 that is to say, it is the first activity of the heemogregarine 

 upon arriving- in the vertebrate host. Miller's (9) account of 

 Hepatozoou perniciosum, Chagas' (5) work on Schizo- 

 trypanum, and Aragao's (1) on H asm o pro tens cblumbae 

 furnish parallels for such an interpretation. On this view the 

 schizogony in the blood-corpuscle would be the later, and, so 

 to speak, chronic process of multiplication, which would at 

 some period culminate in gamete formation. 



I think the evidence is strongest in support of the second view 

 (2) put forward, namely that the schizogony in the lung is the 

 asexual multiplication, and that in the blood gamete-forma- 

 tion. A somewhat important point against view (3) is the 

 fact that the schizont in the lung does not appear to penetrate 

 a lung-cell, which one would expect it to do did it arrive in 

 the lung as a free vermicule (sporozoite). Moreover the 

 possession of an envelope in so early a stage as that shown 



