2 6o SCIENCE PROGRESS 



is obviously impossible to fix any such limit, and size as a 

 -criterion of sex fails entirely. 



The occasional occurrence of two Leucocytozoa within one 

 leucocyte has been observed in the case of L. funambuli and 

 also in certain Leucocytozoa of birds. This is probably merely 

 a case of double infection of the leucocyte, and, though some 

 would consider the two parasites to be sexual forms, neither 

 conjugation nor fertilisation have ever been seen, and until 

 these have been witnessed the question of sex cannot be 

 decided. 



VII. Mode of Transmission 



The exact method of transmission of the mammalian Leuco- 

 cytozoa to fresh hosts has been determined in a few cases 

 only, and even in some of these it is not absolutely certain 

 that the means proved experimentally is the one that occurs 

 naturally or that it is the sole means. Invertebrates — ticks, 

 mites, and lice — have been recorded as the intermediaries for the 

 transference of Leucocytozoa from host to host. 



Christophers (1907) described the sexual cycle of Leuco- 

 cytozoon cam's in the dog tick (Rhipicephalus sanguineus), and 

 this arthropod appears to be the agent in spreading the disease 

 from dog to dog. The exact method whereby the tick infects 

 a new host is not known. Adult female ticks were the ones 

 carrying the supposed vermicules of L. cams, and, as these 

 ticks are supposed not to suck blood again, the possibility of 

 inoculation of the dog by regurgitation of the small sporozoites 

 seems out of the question, and hereditary transmission of the 

 parasite has not been demonstrated. 



Gerrard (1906) also reported that when clean Malay puppies 

 and others infected with L. canis were placed together the clean 

 animals contracted the disease, ticks on the infected dogs being 

 the intermediaries. 



Miller (1908) described the infection of white rats with 

 Leucocytozoon muris {Hepatozoon perniciosum) as occurring in 

 two ways. The rapid method is attained by the rats 

 devouring the mites (Le/aps cchidninus) containing oocysts of 

 the parasite. This was shown experimentally by feeding rats 

 on crushed mites. The slower means of infection is by the 

 bite of the mites, which wander from the rats into the straw, 

 and thence, possibly, to different rats. Whether the rapid 



