ECOLOGY, COMMENSALISM AND PARASITISM 400 



infected corpuscles are uniformly stippled with pink spots, the 

 so-called Schuffner dots. The other 2 species cause no enlarge- 

 ment of the corpuscles, on the contrary there is a tendency to 

 reduce them; Sehiiffner's dots are absent, but irregularly scat- 

 tered larger dots (so-called Maurer's dots) are frequently present 

 in infections by P. falciparum. 



4. While the numbers of merozoites formed by the sporulating 

 individual are not always the same but fluctuate about a given 

 mean, this mean or average is quite different in the 3 species. For 

 Plasmodium vivax it is 16; for P. malariae, about 8; for P. falciparum, 

 about 24. 



5 and 6. During the growth of the parasite granules of dark 

 substance, known as melanin, malarial pigment, etc., and regarded 

 as products of hemoglobin breakdown, are stored up in the Plasmo- 

 dium protoplasm. At sporulation this melanin may be distributed 

 irregularly between the merozoites as it is in P. vivax, or clumped 

 in the center of the group as in P. malariae and P. falciparum. 

 In P. falciparum the merozoites are irregular as in P. vivax, but in 

 P. malarial' they are grouped rosette-like about the clump of 

 melanin (Fig. 12+, p. 2'-\S). 



7. The gametocytes, finally, afford still another diagnostic 

 morphological character. It is limited, however, for there is not a 

 great difference between those of vivax and those of malariae. In 

 P. falciparum they are distinctly differentiated as crescents, the 

 female crescent with a slightly more definite capsule about it than 

 the male crescent (Plate II). All gametocytes are present in the 

 circulating blood with which they are taken into the stomach of a 

 female Anopheline mosquito. 



The evolution of the gametocytes of P. falciparum has recently 

 been studied by Aragao (1930), who finds that there is a distinct 

 difference between the male and female gametocytes which may 

 be traced back to the merozoite stages. Merozoites destined to 

 form male gametocytes after entering a corpuscle are spherical, 

 with a distinct nucleus and without the vacuole typical of ring 

 forms (Plate II). The young female gametocyte, upon entering a 

 corpuscle stretches out across the corpuscle in the form of an 

 elongate bar. In all stages of its evolution the chromatin is more 

 definite than in the male gametocyte. 



The sexual stages in the life history of Plasmodium, consisting 

 of maturation and fusion of the gametes, development of the zygote 

 and formation of sporozoites, all take place in the body of the 

 mosquito. In these processes there is no important difference in 

 the three species. The gametocytes of the circulating blood in 

 which no further development occurs, under the influence of the 

 changed conditions, are stimulated to undergo their maturation 

 processes whereby the female gametocyte becomes a macrogam- 

 ete and the male gametocyte gives rise to a small number of 



