THE H^MOSPORIDIA 377 



number of large merozoites (compare H. canis, below). In both H. gerbilli 

 and H . jaculi free vennicules occur, and are set free readily in vitro ; those of 

 H. gerbilli are recurved when contained in the blood-corpuscle. Stages of 

 the development of H. gerbitti were found in a louse, Hcematopinus stephensi ; 

 first free vermicules in the stomach and intestine, later large cysts in the 

 body-cavity containing a great number of spores, each of which encloses 

 six to eight sporozoites. It seems impossible that the parasites encysted in 

 the body- cavity of the louse should get back into the gerbille in any other 

 way than that of being eaten by the gerbille. Christophers found that, though 

 the sporozoites were liberated in the intestinal juice of the gerbille, they soon 

 died in it, but that in the blood- plasma of the gerbille they became extremely 

 active ; this observation may perhaps be interpreted as indicating that the 

 spores germinate in the intestine, and the sporozoites, when liberated, pass at 

 once through the wall of the intestine into the blood- circulation. 



The crithidial forms seen by Balf our in Pulex cleopatrce can have no connec- 

 tion whatever with the haemogregarine of the jerboa ; the flea is probably not 

 the right host for this parasite. 



A number of leucocytic gregarines have been described from various mam- 

 mals, amongst which may be mentioned H, canis (Christophers, 700), H. 

 funambuli (Patton, 721), and H. musculi (Porter). The life-cycle of H. canis 

 has been described by Wenyon (84). The schizogony takes place in the bone- 

 marrow and the spleen of the dog, and is of two distinct types. In the one 

 case the schizont divides into a small number of merozoites, usually three, 

 of large size. In the second case the schizogony results in the production cf 

 a large number of small merozoites. The larger merozoites grow up into 

 schizonts again ; the small merozoites pass into the blood, are taken up by 

 the leucocytes, and become the gametocytes, as in H. muris. The sporogony 

 takes place in the tick, Rhipicephalus sanguineus, and is similar throughout 

 to that of H. muris. The sexual phases were not observed by Wenyon, but 

 according to Christophers (701) the vermicules become free in the stomach, 

 and penetrate the epithelial cells, in which they multiply by fission to form 

 gametes ; probably this applies to the male sex alono. The next stage is an 

 oocyst in the tissues of the tick. The oocyst grows in size, its nuclei multiply, 

 some thirty to fifty uninucleate sporoblasts are formed, and each secretes 

 a sporocyst and becomes a spore containing on the average sixteen sporozoites. 

 The oocyst-wall dissolves, and the ripe spores are set free in the body of the tick. 

 Wenyon considers it possible that the dog acquires the infection by eating 

 infected ticks. 



Free vermicules of H. funambuli were seen in a louse by Patton, and a similar 

 observation was made for H. musculi by Porter. H. musculi also reproduces 

 by schizogony in the bone-marrow of its host. 



The haemogregarines of birds described by Aragao (692) appear to be very 

 similar to those parasitic in the leucocytes of mammals. The schizogony 

 takes place in the epithelial cells of the gut or in the cells of the liver, lung, or 

 bone-marrow 9 it results in the formation of a number of small, comma- 

 shaped merozoites, which escape from the cell and are taken up by the mono- 

 nuclear leucocytes. They do not, however, remain- in a resting phase in the 

 leucocytes, but grow within them to a fair size. When set free from the 

 leucocyte, they perform active movements. The intermediate host and the 

 mode of transmission remain, however, to be discovered. 



The schizogony of hsemogregnrines parasitic in snakes has been studied 

 by Sambon and Seligmann, Hartmann and Chagas (89), and Laveran and 

 Pettit (716). It takes place in the capillaries of the liver and lung or in the 

 bone-marrow. The parasite becomes free from the corpuscle in the capillary, 

 and grows to a large size. In H. sebai the number of merozoites formed 

 varies from two or four to over thirty, but is more often from four to eight. 

 The merozoites are larger when a smaller number is produced. Possibly the 

 variation is related to the age of the infection, as in H . stepanowi, or to the destiny 

 of the merozoites, whether to become schizonts or gametocytes, as in H. canis. 



The sporogony of the haemogregarines of terrestrial reptiles is practically 



