1 78 COMPARATIVE ANATOMY 



with the saliva into the wound when the insect sucks blood. 

 On entering the blood vessels they at once attack and make 

 their way into the red blood corpuscles, just as the sporozoite 

 of Monocystis attacks and enters the sperm-mother cell of an 

 earthworm. 



Fig. 38- 



A diagram illustrating the stages of the life cycle of Plasmodium vivax 

 found in human blood. I-IX show the schizogonous cycle. In / a 

 sporozoite is boring its way into a red corpuscle ; 77, young amoeboid 

 phase_; 777, a vacuole has appeared near the nucleus giving the charac- 

 teristic ring form ; 7Fand p", pigment (melanin) granules are deposited 

 in the cytoplasm, the parasite has increased in size and exhibits active 

 pseudoppdial movements; F7, nucleus with an equatorial ring of 

 chrpmatin granules ; VI[ and VIII, successive stages of nuclear 

 division ; 7 A', segmentation of the cytoplasm round the nuclei to form 

 the merozoites which are shown at mer escaping into the blood plasma, 

 j/z, sporozoites ;/, pigment granules ; gam, a young gametocyte ; <$ , a 

 male gametocyte (microgametocyte) and O_ a female gametocyte 

 (macrogametocy te) of P. vivax. In this species and in P. malaria thr 

 gametocytes are not crescent-shaped as they are in P. immaculatum. 

 (Somewhat diagrammatic after Schaudinn.) 



Each sporozoite is a minute spindle-shaped cell, pointed at 

 both ends with a nucleus in the middle of its body (fig. 38, 

 spz). It has been observed, in a drop of blood kept under 

 suitable conditions of warmth and moisture under the micro- 

 scope, to move actively among the corpuscles either by wave- 



