THE LEUCOCYTOZOA 261 



method of infection is a natural one is open to criticism. If 

 it were so, the faeces of the rats should contain the chitinoid 

 remains of the mites, but we are not told that such was the 

 case. If this method of infection occurs naturally, then we 

 have an entirely new method of infection, whereby the 

 vertebrate host eats the ectoparasitic invertebrate carrier. 



Miller's experiments were most ingenious. However, in such 

 a complicated subject, mistakes cannot be entirely excluded, and 

 it is just possible that Miller's sporogonic stages of Hepatozobn 

 perniciosum in the mite were stages of natural parasites of the 

 mite {e.g. a Gregarina or Coccidium, or both). This remark is not 

 intended as in any sense derogatory to Miller's work, which 

 was most clear and original. One cannot, however, overlook 

 the fact that many most capable observers have for several 

 years failed to find any evidence of a sexual cycle of a Leuco- 

 cytozoon in an invertebrate (arthropod) carrier of infection. 



Lice act as agents of transmission of disease in the case of 

 L. musculi. Lice fed on infected white mice showed vermicules 

 in their gut, and similar ones placed on clean mice produced 

 a slight infection. No sexual cycle of the Leucocytozoon has 

 been seen in the louse {Hcematopinus spinulosus), and it is 

 probable that the hemipteran acts merely as a mechanical agent 

 in the transference of the disease. 



The mode of transmission of the Leucocytozoa of birds and 

 amphibia is unknown. 



VIII. Distribution 



The Leucocytozoa occur in all parts of the world, though 

 they are more abundant in the leucocytes of animals 

 living in tropical regions. Several Leucocytozoa — e.g. L. canis, 

 L. funambuli, L. fells domestical, L. leporls, and L. ratti (a variety 

 of L. muris) — occur in various parts of India. Also, in dogs 

 from Malay and Tonkin, L. canis has been found. So far as 

 mammalian Leucocytozoa are concerned, the majority are found 

 in Asia. 



Leucocytozoa also occur in Africa, for many of the avian 

 Leucocytozoa are found there. The chief mammalian form from 

 Africa is L. muris, described by Balfour from the leucocytes 

 of Mus decumanus at Khartoum. 



Up to the present the only Leucocytozoon described from 

 European mammals is L. musculi, which occurred in white 



