9 8 



THE ANIMAL PARASITES OF MAN 



The development of the sporonts in mosquitoes (of the genus 

 Anopheles) is dependent on the atmospheric temperature and the 

 species of parasite. The plasmodium of the malignant tertian 

 (tropical fever) completes its development within eight days at a 

 temperature of 28 30 C. ; below 18 C. the development ceases. 

 The same condition also holds good for Plasmodium vivax, whereas 

 Plasmodium malarice requires a lower temperature, that is to say, 

 it will still develop at i6'5 C., but not if the temperature is 

 over 30 C. 



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FIG. 41. Ookinets of pernicious parasites 

 in the stomach of Anopheles maculipennis 

 thirty- two hours after having been sucked in. 

 (After Grassi.) 



FIG. 42. Transverse section of 

 the stomach of an Anopheles, with 

 cysts of the pernicious parasites. 

 (After Grassi.) 



The oocysts resting in the intestinal wall are at first oval, 

 but with their further growth they become globular. First of 

 all the nucleus within them divides up into a large number of 

 daughter nuclei. A portion of protoplasm gathers round each one 

 of these nuclei, and thus a number of mononuclear polyhedric cells 

 are formed and connected one with the other by bridges of proto- 

 plasm which occupy the entire internal space of the cystic mem- 

 brane (fig. 43, a). These cells may be termed sporoblasts, but 

 contrary to the similarly termed forms in coccidia, they remain 

 naked and immediately form the sporozoites. This process begins 

 by a division of the nucleus in each sporoblast ; the numerous 

 daughter nuclei take up a peripheral position in the plasma of 

 the sporoblasts and receive a thin coating of hyaline proto- 

 plasm. The entire substance of the sporoblast is not, however, 

 consumed thereby ; the larger part remains undivided, becomes 

 elongated and granular ; it represents a residual body which is 

 surrounded by numerous roundish sporozoites (fig. 43, b and c). 

 The sporozoites soon become small, elongated forms pointed at 

 both ends, one of which still adheres to the residual body. The 



