THE H^MOSPORIDIA 375 



destined to grow into gametocytes (Fig. 1 59, J L) . In H . stepanowi 

 the microschizont sporulates in the bone-marrow or in the circu- 

 lating blood, and produces six micromerozoites. In H. nicorice 

 it sporulates only in the circulating blood, and produces six to 

 eight micromerozoites. 



(4) The micromerozoites penetrate into a blood-corpuscle, and 

 may (a) repeat the microschizogony, or (6) develop into sporonts- 

 (gametocytes). 



(5) The sporonts (Fig. 159, M l , M z ) are sexually differentiated. 

 They represent the end of the. development in the tortoise, and can 

 only develop further in a leech. H. stepanowi develops in Placob- 

 della catenigera (=Hcementeria costata), H. nicorice in Ozobranchus 

 shipley i. 



(6) When the leech sucks the blood of an infected tortoise, it 

 may take up every stage of the parasite into its stomach, where, 

 however, all stages are digested except the sporonts, which resist 

 digestion and pass on into the intestine. There they associate in 

 couples, male and female together. The male sporont produces 

 four microgametes, and one of the four penetrates the macrogamete 

 and fertilizes it (Fig. 159, N R). 



(7) The zygote forms an oocyst with a thin membrane, and 

 divides within it into eight sporozoites (Fig. 159, S U], which 

 pass into the blood-spaces and collect in the dorsal blood-vessel of 

 the leech. How they pass from thence into the tortoise is 

 uncertain. 



The existence of two types of schizogony macrocysts producing macro- 

 merozoites, and microcysts producing micromerozoites in the cycle of the same 

 species of haemogregarine, has long been known, but without the significance 

 of this fact being understood. 



While the life-history described above is very probably typical of the hsemo- 

 gregarines of aquatic cold-blooded vertebrates, where the intermediate host 

 is a leech, that of terrestrial animals, so far as it is known, is of a somewhat 



FIG. 159 continued : 



A, Sporozoite ; B, C, early schizogony, in which a large number of mero- 

 zoites are produced ; D, merozoite penetrating a blood-corpuscle ; E U, 

 later schizogony, in which few merozoites are produced ; in F the reorrvcd 

 vermicule within the corpuscle is seen ; /, free merozoite about to penetrate 

 a corpuscle and recapitulate the stages D H, or to initiate the next phase ; 

 J, K, the stages of the final schizogonous generation which produces the 

 gametocytes ; L 1 , L 2 , sexually-differentiated mer^zoites of the final generation, 

 which grow up into male (If*) or female ( M 2 ) gametocytes respectively ; these 

 are the stages which develop in the leech when taken up by it. 



N, Association of male and female gametocytes in the gut of the ieech ; 

 0, formation of four male gametes by the male gametocyte ; P, one of the 

 male gametes has penetrated into the body of the female gamete, and the 

 two pronuclei are undergoing fusion, with formation of a fertilization-spindle ; 

 Q, zygote with synkaryon and the degenerating remains of the male gameto- 

 cyte attached to it, which is seen also in the next four stages ; R, 8, T, succes- 

 sive divisions of the synkaryon ; U, ripe cyst containing eight sporozoites, 

 residual protoplasm, and the remains of the male gametes. 



After Reichenow (78), modified in arrangement. 



