164 GENERAL BIOLOGY OF MICRO-ORUANISMS 



host, the mosquito. In the stomach of this insect the gametes 

 unite and the fertilized cell (ookinet) actively penetrates the 

 epithelium and beneath it develops into a large oocyst, 30 to 90/* 

 in diameter, enclosed in the elastic tunic of the stomach wall of the 

 mosquito. As the oocyst enlarges, the nucleus divides and eventu- 

 ally the cytoplasm also. The nucleus of each of these masses 

 (sporoblasts) then divides many times. Each nucleus, together 

 with a small amount of protoplasm, separates and then elongates 

 into a slender thread-like sporozoit (14 X im)- As many as 10,000 



Pig. 82. — Babesia muris. A, Young form in a red blood cell. B, Form with 

 two nuclei. C and D, Binary division. E and F, Multiple infection; ameboid 

 forms in F. G, An exceptionally large individual (gametocyte?). H, Form with a 

 thread-like process (flagellated stage ?) . (From Doflein after Fantham.) 



of these may be produced in one oocyst. The cyst bursts into the 

 body cavity of the mosquito and the motile sporozoits circulate 

 through the body of the insect and eventually assemble in the cells 

 of the salivary glands. From these they escape with the secretion 

 and gain entrance to the wound made by the mosquito in biting. 

 Babesia. — A number of parasites of the red blood cells are 

 classed in the genus Babesia {Piroplasma) . These resemble the 

 members of the preceding genus very closely but multiple division 

 (segmentation) does not seem to occur in the asexual cycle. The 

 multiplication seems to be by longitudinal division into two 

 daughter cells. The characteristic form is pear-shaped, but 

 irregular amoeboid forms are also common. Flagellate stages 

 existing in the blood plasma have also been described. The sexual 



