STUDIES ON CKYLON H^MATOZOA. 743 



The liaeiiiogregai-ine in the blood of the tortoise shows the 

 usual two types, a bean-shaped and a recurved type. Certain 

 of tlie beau-shaped individuals, namely, the large forms with 

 a nucleus in which the chromatin is rather loosely arranged, 

 give rise by a process of schizogony in the lung to a great 

 number (about seventy) of large merozoites. Another type 

 of schizogony is found in the circulating blood-corpuscles, 

 and arises also from bean-shaped individuals. This results 

 in the formation of a small number (six to eight) of mero- 

 zoites of quite small dimensions. It appears that the form 

 which gives rise to this second type of merozoite is itself 

 derived from the schizogony in the lung. It is probable that 

 the small merozoites give rise to the gametocytes. The reason 

 for this assumption is given in another part of the paper. 

 When the heemogregarines are taken into the crop of the 

 leech, Ozobranchus shipleyi, together with the blood of 

 the tortoise, certain of the hasmogregarines pass into the 

 intestine, and are there found as motile vermicules. They 

 penetrate into the intestinal wall, where the differentiation of 

 the hitherto indistinguishable gametes takes place, culminating 

 in a process suggesting anisogamous conjugation. The 

 zygote breaks up to form eight sporozoites, which pass 

 through the intestinal wall into the blood-spaces. The 

 haemogregarine is probably passed into the blood of the 

 I^icoria through the contamination of the wound by the leech 

 while feeding. 



III. Phases of the Hj]mogregarine in the Blood op the 



Tortoise. 



In the living state the hasmogregarine may easily be dis- 

 tinguished as a clear sausage-shaped inclusion in the red 

 blood-corpuscles. The protoplasm is slightly more granular 

 at one end than the other, and the nucleus can be seen as a 

 sharply defined clear area. The parasites do not show any 

 sign of movement when they are observed upon a sealed 

 slide, but free vermicules are very occasionally found in 



