712 MISS ANNIE PORTER ON A [June 16, 



other. However, the formation of a definite zygote from these 

 associated forms was, unfortunately, not seen. 



Again, in PI. XXXIX. Jig. 22, those authorities who believe in 

 differentiation into male and female forms, would see a female 

 form (macrogametocyte) in the upper, broader and granular 

 parasite, and a male form (microgametocyte) in the lower, longer 

 and narrower form. I do not go quite so far personally, as I have 

 doubts of sexual differentiation, preferring the series view (see 

 page 707). However, in the present state of our knowledge, the 

 suggestion of sexual forms is worthy of note. 



IX. Life-History. 



Commencing with the free vermicule which may be either a 

 sporozoite or a merozoite, the following sequence probably occurs. 

 The parasite lives awhile in the plasma as a small, active form 

 (PI. XXXIX. fig. 13). This ultimately penetrates a leucocyte 

 and grows actively there as an endoglobular trophozoite. A 

 cytocyst may or may not form around it (PI. XXXIX. figs. 15, 

 16, 17). After a time, it becomes free in the plasma, rviptuiing 

 the host-cell as it issues, but leaving little or no trace of its 

 presence behind. In the plasma it assumes the free trophozoite 

 form. Association between trophozoites may perhaps occur (cf, 

 PI. XXXIX. figs. 21, 22), and the residt of this is probably a 

 zygote, which one would expect to find in the louse, on homology 

 with the malarial parasite — but more definite information is 

 lacking. 



Other free forms may reach the bone-marrow. There encyst- 

 ment occurs, and a schizont, in a thin but distinct cytocyst, is 

 produced. This schizont by multiple fission gives rise to relatively 

 few but definite merozoites. By the rupture of the cyst, these 

 are set free into the blood-stream where growth again occurs, 

 leading to adult trophozoites. This is the schizogonic cycle of the- 

 parasite. 



Ecto-parasitic on the mouse was the louse, Hoemato'pi'nus 

 s2nnulosus. By the bite of this louse infected blood passes from 

 the mouse to the mouth and gut of the invertebrate host, and so 

 we find the small, gregarinifoi'm vermicviles shown in PI. XXXIX. 

 figs. 23, 24. These ultimately reach the saliva of the louse and 

 by this insect are probably transferred to another mouse. PerhajDS 

 a sexual cycle of the Leucocytozoon occurs in the louse, but of 

 this I have, unfortunately, no definite evidence. Probably the 

 louse is merely a mechanical agent in spreading the infection. 



X. Affinities of the Parasite, and Summary. 



Affinities of Parasite. 



The term Leucocytozoon was used by Danilewsky [8] in 1890 

 for vermiform parasites stated to occur in the leucocytes of certain, 

 birds. Danilewsky confined his observations to fresh preparations. 



