370 THE PROTOZOA 



is occupied by an oval, compact mass of cytoplasm containing a 

 nucleus. By some this mass is regarded as the whole parasite, by 

 others as its endoplasmic region alone. In the female forms the 

 cytoplasm is dense and stains deeply, and the nucleus is relatively 

 small, with a distinct karyosome sometimes placed eccentrically. 

 In the male forms the cytoplasm is paler, and the much larger 

 nucleus stains feebly, with a diffuse granular structure and with- 

 out a conspicuous karyosome. Stretched along one side of the 

 body of the parasite is the nucleus of the host-eel] compressed, 

 usually more or less drawn out, and staining deeply. The surface 

 of the body is covered by a thin membrane, which is prolonged 

 usually into two horn-like processes at the two poles of the body. 

 It is doubtful whether these two processes consist solely of the 

 substance of the host-cell, or whether they contain ectoplasmic 

 extensions of the parasite also. In any case it is certain that the 

 parasite modifies the host-cell in a singular manner. It is also 

 disputed whether the host-cell itself is an erythroblast or a mono- 

 nuclear leucocyte. Most recent investigators, however, incline 

 to the latter view ; but Keysselitz and Mayer (A.P.K., xvi., p. 237) 

 state that the host-cell is an erythroblast. No melanin -pigment is 

 formed. 



The young forms of the parasite are compact, rounded, or 

 haemogregarine-like, contained in white cells with a large nucleus, 

 and without the horn-like processes characteristic of the adult. 

 Fantham (689) has described in L. lovati of the grouse multiplica- 

 tion by schizogony taking place in the spleen. The schizonts pro- 

 duce a number of merozoites which escape into the blood, and 

 doubtless give rise to the j'oung forms of the leucocyte zoa. The 

 periodicity of the sexual forms in the blood observed by Mathis 

 and Leger (473) depends, probably, on successive schizogonous 

 generations occurring in the internal organs, such as Fantham has 

 described. 



The method of transmission and the invertebrate host are as yet 

 unknown. If blood containing the parasites in the condition of 

 ripe gametocytes be drawn, the sexual phases and fertilization can 

 be studied without difficulty on the slide. The female gametocytes 

 round themselves off, losing their spindle-like form, and burst their 

 envelope. The male gametocytes contract themselves into two or 

 three rounded masses, which give off about eight thread-like 

 microgametes altogether, in a manner similar to the " exflagel- 

 lation " of the malarial parasites. The microgametes become de- 

 tached and fertilize a female. 



Schaudinn-(132) gave an account of the development of these parasites 

 which cannot be accepted as correct. According to him, L. ziemanni of 

 Athene myetiia is in reality the resting stage of a large trypanosome, which 



