THE LEUCOCYTOZOA 259 



sexual cycle of the rat parasite that he called Hcpatozoon perni- 

 ciosum, which is probably L. muris. The cycle takes place in 

 the mite Lelaps ecktdnmus, and as this is migratory, infection of 

 other rats is easily brought about. Miller describes schizogony 

 of the usual type as occurring in the liver of the rat, and by 

 this means numerous merozoites are set free into the blood- 

 stream. These penetrate the leucocytes, and finally encyst. 

 Mites, when feeding on the rats, swallow the encysted Lencocy- 

 tozoa, which are liberated in the stomach of the mite as free 

 vermicules. These vermicules were described by Miller as 

 "similar," and "two similar vermicules become associated and 

 conjugate." One, the female or macrogamete, grows larger and 

 partly surrounds the other, the male or microgamete. After 

 the association the nuclei fuse to form a zygote, which gives 

 rise to a sluggishly motile body, that, in the course of its 

 wanderings, penetrates the stomach wall of the mite, encysts 

 there, and becomes the oocyst. The nucleus of the oocyst 

 divides into many parts, which travel to the periphery, and the 

 surface of the growing oocyst becomes raised into rounded 

 projections. Each projection contains several nuclei, becomes 

 detached, and forms a sporoblast. Finally the sporoblasts 

 acquire a cyst wall, and, within the sporocyst so produced, 

 sixteen minute parasites, the sporozoites, are formed. As each 

 oocyst contains fifty to a hundred sporocysts, the number of 

 sporozoites is very great. The sporozoites serve to infect other 

 rats. The possibility of the infection of the mite by a parasite 

 peculiar or natural to itself, stages of which might be mistaken 

 for stages of sporogony of the Leucocytozoon, must not be 

 overlooked. 



Up to the present there is no definite evidence that un- 

 doubted sexual differentiation occurs either in the Haemo- 

 flagellates or in the Leucocytozoa of the mammalian blood. Some 

 workers, influenced perhaps by what occurs in the malarial 

 parasite, have been led to declare that male and female forms 

 exist. They argue that shorter, thin forms, with sometimes a 

 slightly denser nucleus, are male ; while larger, broader forms, 

 with a somewhat less chromatic nucleus and granular proto- 

 plasm, are regarded as female. Careful examination of the 

 dimensions and figures given for the two forms of parasites 

 shows that they merely form a continuous series. Where, then, 

 in a series is the limit for, say, male forms to be applied ? It 



