CHAPTER XXII 



ORDER 2 HAEMOSPORIDIA DANILEWSKY 



THE DEVELOPMENT of the Haemosporidia is, on the whole, 

 similar to that of the Coccidiain that they undergo asexual 

 reproduction, or schizogony, and also sexual reproduction, or 

 sporozoite-formation ; but the former takes place in the blood 

 of vertebrates and the latter in the alimentary canal of some 

 blood-sucking invertebrates. Thus one sees that the Haemo- 

 sporidia do not pass any part of their development outside of 

 a host body; hence, the sporozoites do not possess a resistant 

 membrane. 



The Haemosporidia are minute and usually intracellular 

 parasites of erythrocytes. The malarial parasites of man are 

 typical members of this order. The development of Plasmodium 

 vivax is as follows (Fig. 120): Infected anopheline mosquitoes 

 introduce the sporozoites (a), which invade the erythrocytes 

 {b), grow, and undergo schizogony, forming a number of mero- 

 zoites (c-/). The latter upon liberation from the host cells, at- 

 tack other erythrocytes. Some of the merozoites become macro- 

 gametocytes (g) and others microgametocytes {i, j). No fur- 

 ther changes ordinarily take place in the human body, but the 

 schizogony is repeated. The protozoan produces melanin (or 

 haemozoin) which is apparently the matabolic product of the 

 organism at the expense of the haemoglobin. When the 

 blood is taken into the stomach of a suitable species of anophe- 

 line mosquito, the gametocytes undergo development, forming 

 macrogametes and microgametes {h, k). They unite in pairs 

 (/) and thus ookinetes (zygotes) (w) are formed. The ookinetes 

 penetrate the stomach wall and become lodged between the 

 epithelium and the elastic membrane of the stomach («). 

 There they grow and the nuclei undergo rapid and repeated 

 divisions, finally producing an enormous number of minute 

 sporozoites {o, p). These sporozoites are set free through the 

 rupture of the cyst wall in the body cavity, find their way into 

 the salivary glands and wait for an opportunity of being inocu- 



[284 1 



