LIFE-CYCLE OF " CYSTOBIA " IRREGULARIS (mINCH.). 71 



Flagellate became specially adapted for life in the blood. 

 With the acquirement of an alteration of hosts the life- 

 history has become extremely complicated, but the details do 

 not concern as here. It is probably in this order, however, 

 that the Flagellate phase is retained to the greatest extent. 



The Coccidia are to be regarded as having resulted from 

 the original parasite becomiug entirely intra-cellular. With 

 this is correlated their uon-raotility and the great specialisa- 

 tion which we find in the sexual process. The numerous male 

 gametes are highly differentiated and constitute, so far as is 

 known at present, the only phase in the life-cycle where the 

 Flagellate ancestry becomes manifest. The female individual, 

 or megagametocyte,^ no longer divides up to form many 

 gametes, but itself becomes one directly after nuclear re- 

 duction. In Cyclospora, however, Schaudinn has recorded 

 (34) certain abnormal cases of the persistence and further 

 multiplication of tlie "reduction nuclei" of the female 

 element, followed by multiple fertilisation. This occurrence 

 points very strongly to the conclusion that there were ori- 

 ginally many female gametes also, a condition which would 

 agree with that found in Gregarines. 



Lastly, we come to the Gregarines, Avhich are by far the 

 most successful group. I do not agree with Minchin (26, 

 pp. 272, 273) in considering this order (any more, indeed, 

 than the other Telosporidia) as derived from an originally 

 intra-cellular form, which re-acquired, secondarily, an inter- 

 cellular habitat. It is much more likely that the Gregarines 

 have never been entirely intra-cellular, since, in that case, it 

 is almost certain they would have completely lost their 

 mobility and any cytoplasmic differentiation they possessed. 

 Moreover, the female individuals would also have tended to 

 reduce the number of gametes, of which we find no trace. 



Whereas, in the evolution of the Coccidia, the young para- 

 site at length penetrated completely into the host-cell and 

 stayed there, in no instance do we find such an advanced 



1 In many Coccidia bisexual differentiation becomes marked in the adult 

 trophozoites, or even earlier. 



