420 ZOOLOGY. 



nuclei, which assume an elongated form and then separate 

 from the gametocyte, each provided with a protoplasmic 

 flagellum at each end (Fig. 206, & $ ). In the female 

 gametocyte, on the other hand, it is the chromatin 

 which remains at the centre while the achromatic 

 part of the karyosome is expelled at the circumference in a 

 fashion which reminds one of polar bodies, though there 

 seems to be no real similarity between the two cases. The 

 female gametocyte also accumulates a certain amount of 

 food granules resembling the yolk of the Metazoan ovum. 



12. Conjugation. A microgamete enters the mega- 

 gamete, and fuses with its chromatin nucleus, and the 

 result of this process of conjugation or fertilisation is the 

 zygote. The nucleus next divides by direct division into 

 four, and the protoplasm also segments, forming four 

 sporoblasts. The zygote surrounds itself with a cyst called 

 the oocyst. Each sporoblast also becomes enclosed in a 

 thick coat called the sporocyst, and the contents of the 

 spore divide into two sporozoites. We thus reach the 

 stage from which we started in following the succession of 

 stages in the life-history. 



13. Mode of Infection. The infection of a Lithobius 

 is due to the accidental swallowing of oocysts with the 

 food. The parasite is intracellular in all stages except the 

 free sporozoites and merozoites, which enter new epithelial 

 cells and there develop. When the oocysts are developed 

 they become free in the intestine of the host and then pass 

 out with the faeces. When these oocysts are swallowed by 

 another Lithobius, the cyst wall is dissolved by the diges- 

 tive secretions, the four spores are liberated, and then 

 each spore splits lengthwise and the sporozoites are 

 liberated and at once make their way into the epithelial 

 cells of the intestines. 



14. Life-history Formula. The life-history of Cocci- 

 dium schubergi is represented in the following formula : 

 Sporozoite -> schizont x merozoites -> . . . schizonts -> 



-> merozoites -> $ gametocytes x n <$ gametes ) , _ 

 . . . merozoites ->- ? gametocytes -> ? gametes j 

 zygote x 4 spores X 8 sporozoites. 



