LIFE-CYCLP] OJ? "OYSTOBIA" IRREGULAEIS (mIKCH.). 79 



zoites are not ready to encyst permanently, may well suffice, 

 under certain modified conditions, to impart the essential 

 developmental stimulus. 



Gregarine "chains." — A word or two, finally, with 

 regard to the curious "chains" or aggregations of Gre- 

 garines, such as are known to occur, for example, in Eirmo- 

 cystis, Clepsydrina, etc. Their significance is very 

 problematical. It is possible that the cytotactic attraction 

 has become modified in function. Its primary object, to 

 induce the formation of gametes, being, as in Di plod in a, 

 delayed or in abeyance, it may perhaps serve a subsidiary 

 purpose in trophic life. 



Isogamy, in the Gregarines, is to be regarded as 

 the more modified, and not as the more primi- 

 tive, condition. 



In conclusion, it may not be superfluous to point out some 

 of the reasons why the general course of evolution above out- 

 lined seems to me to have much more in its favour than what 

 is practically the opposite view. I should, indeed, hardly 

 consider it necessary to do so were it not that this contrary 

 view has been recently supported by Brasil (3), and Nusbaum 

 (28). Both these authors consider isogamous copulation to 

 represent the more primitive condition in the order. Brasil 

 regards the case of Urospora and Gonospora as marking 

 an early stage in the evolution of anisogamy, the highest 

 development in this direction being attained by Ptero- 

 cephalus. Nusbaum thinks that association at first was 

 well developed, and served as a stimulus to the two mem- 

 bers, which gave rise to isogamous gametes (example, 

 Lankesteria). Subsequently, the process became less 

 important, the two associates not entering into such inti- 

 mate contact ; correlated with this we have the formation 

 of male and female elements (example. Sty lorhy nchus). 

 Lastly, the association has a quite transitory significance, and 

 is, in short, a reduced phenomenon; the associates themselves 



