Chapter 25 

 Order 3 Haemosporidia Danilewsky 



THE development of the Haemosporidia is, on the whole, sim- 

 ilar to that of the Coccidia in 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 Haemosporidia 

 remain always within the body of one of the two hosts; hence, the 

 sporozoites do not possess any protective envelope. 



The Haemosporidia are minute intracorpuscular parasites of 

 vertebrates. The malarial parasites of man are tj^pical members 

 of this order. The development of Plasmodium vivax is as follows 

 (Fig. 197) : Infected anopheline mosquitoes introduce the sporo- 

 zoites (a) which invade the erythrocytes (6), grow, and undergo 

 schizogony, forming a number of merozoites (c-f). The latter 

 upon liberation from the host cells, attack other erythrocytes. 

 Some of the merozoites develop into macrogametocytes (g) and 

 others, microgametocytes (i, j). No further changes ordinarily 

 take place in the human body, but the schizogony is repeated. 

 The protozoan produces melanin (or haemozoin) which is appar- 

 ently the metabolic product of the organism at the expense of the 

 haemoglobin. When the blood is taken into the stomach of a suit- 

 able species of anopheline mosquito, the gametocytes develop 

 into macrogametes and microgametes respectively (h, k). They 

 unite in pairs (I) 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 (n). 

 There they grow and the nuclei undergo rapid and repeated divi- 

 sions, finally producing an enormous number of minute sporo- 

 zoites (o, p). These sporozoites are set free through the rupture 

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

 vary glands and wait for an opportunity of being inoculated into 

 a new victim (q). The schizogony occurs regularly, and it is 

 thought that the typical malarial fever is caused by some toxic 

 substances which are liberated into the blood stream when in- 

 numerable merozoites become set free in the latter. 



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