Sporozoa 307 



6. 23, H) divide into uninucleate forms, some of which enter the blood 

 stream and invade red corpuscles. The erythrocytic forms (Fig. 6. 23, 

 I-S) are infective for ticks. 



The life-cycle of Babesia bigemina (26, 27), the causative organism of 

 Texas cattle fever, is similar to that of Theileria parva. Erythrocytic 









Fig. 6. 23. A-F. Theileria parva, stages in ticks (after Cowdry and Ham): 

 A. Group of three "zygotes," x4550. B. Ookinete in gland cell. C, D. Growth 

 of ookinete. E. Multinucleate sporoblast. F. Sporozoites surrounding a resid- 

 ual inass; B-F, x2925. G-S. Theileria pama, stages in cattle (after Cowdry 

 and Banks): G. Multinucleate "agamonts" in a lymphocyte, x2925. H. A 

 multinucleate "gamont" in a lymphocyte, x2600. I-P. Stages suggesting re- 

 production of T. parva in red corpuscles; x2925. Q-S. Corpuscles containing 

 two, three and ten parasites; x2925. 



Stages are ingested by the tick and liberated from the corpuscles (Fig. 6. 

 24, K-M). Elongated "isogametes" later appear and undergo apparent 

 isogamy (Fig. 6. 24, N-R). The zygotes become ookinetes which migrate 

 through the gut wall. Those which invade ova continue their develop- 

 ment in the resulting young ticks, j^roducing sporoblasts (Fig. 6. 24, 

 S-W) which become sporokinetes. Some of these sporokinetes invade cells 



