258 SCIENCE PROGRESS 



schizont has a single nucleus. This nucleus divides into a 

 number of fragments, around each of which protoplasm collects, 

 producing a small daughter form. In L. cam's at least thirty 

 such daughter forms or merozoites are produced (fig. 4, a), 

 arranged about the periphery of the cyst wall. In L. maris the 

 nuclei of the dividing schizont migrate to the poles of the cyst, 

 and the total number of merozoites is about sixteen, arranged 

 in two groups, one at each end of the cyst (fig. 4, b). The 

 merozoites of L. musculi (fig. 4, c) are also few in number, some 

 ten to twelve, usually arranged in couples within the cyst. 

 A small amount of the protoplasm of the parent schizont may 

 be left over in merozoite formation, and remains behind in the 

 cyst (fig. 4, a-c). The merozoites are small and usually falciform 

 or vermiform. They become free within the cyst, whose walls 

 ultimately break down, so setting free the minute parasites into 

 the blood-stream, where they infect other leucocytes. The 

 remains of the cell in which encystment of the schizont occurs 

 are found outside the cyst. Schizogony of the Lcucocytozoa has 

 never been observed in the peripheral blood. 



(b) Sexual Reproduction. — Possible sexual methods of repro- 

 duction in Lcucocytozoa have been rarely observed, and in the 

 cases that have been described there is a certain amount of 

 doubt, owing to the possible occurrence of natural parasites 

 of the invertebrate host, within which the sexual reproduction 

 of the parasite is supposed to occur. The earliest record of 

 sexual reproduction is that made by Christophers (1907), who 

 described a developmental cycle for L. cauis in the dog tick 

 (Rhipiccphalus sanguineus). Christophers removed ticks from 

 dogs heavily infected with Leucocytozoon canis. The ticks were 

 immediately dissected, and free vermicules were found in their 

 guts. Each vermicule penetrates the gut epithelium of the tick, 

 and there divides into two, then four, and sometimes eight 

 smaller individuals. These secondary vermicules conjugate in 

 pairs, and, as a result of fertilisation, oocysts are formed. These 

 are about 14 fi in diameter, are oval in shape, and within each, 

 twelve to fourteen small, sausage-shaped, sexually produced 

 parasites, the sporozoites, are differentiated. The possible 

 existence of a natural parasite of the dog tick (e.g. a Coccidium) 

 needs very careful consideration in connection with this supposed 

 sexual cycle of L. canis. 



The late Surgeon W. W. Miller (1908) recently described a 



