SPOROZOA 



437 



cyte and enlarges, retaining its oval or circular form. The nucleus 

 of the host cell is pushed out of position but its form is not ma- 

 terially altered. The full-grown parasite segments, producing 

 lo to 30 merozoits and leaving behind a small residual body con- 

 taining the accumulated pigment, thus completing the asexual 



Pig. 196. — Proteosoma prcecox in the blood of a field lark (Glauda arvensis). 

 A, Young parasite in a blood cell. B, Half-grown parasite which has pushed aside 

 the nucleus of the erjrthrocyte. C, Parasite with clump of pigment and many nuclei. 

 The nucleus of. the erythrocyte has been lost (uncommon) . D, Division into eight- 

 een merozoits. (From Doflein after Wasielewski.) 



cycle, which may be repeated many times. After a time some 

 of the growing parasites become differentiated to form macro- 

 gametocytes and microgametocytes, which are kidney-shaped and 

 do not divide nor undergo further development in the vertebrate 

 host. When the blood is drawn and diluted with citrated salt so- 



FlG. 197. — Midgut of a culex mosquito, covered with oocyts of Proteosoma prcecox. 

 V, Vasa malpighii. (From Doflein after Ross.) 



lution, or taken in by a mosquito, four to eight microgametes are 

 formed just as has been described for H. columbce. They are very 

 slender actively motile spindles without flagella. Fertilization 

 of the macrogamete and the production of an ookinete takes 

 place in the usual manner. The latter penetrates the intestinal 

 epithelium of thfe mosquito (Culex sp.) and enlarges to produce 



