LIFE-CYCLE OF " CYSTOBLl " IREEGULAEIS (mINCH.). 81 



cation of parthenogenetic reproduction. It would seem 

 rather as if these isogamous forms could not become (again) 

 anisogamous. 



The Coccidia are very interesting in this connection. From 

 what has been said above, it follows that, if permanent asso- 

 ciation together with isogamy is to be regarded as the more 

 primitive condition in the Grregarines, it was probably also 

 a feature of the ancestral Coccidiau. We might, there- 

 fore, reasonably expect to find association persistent, in some 

 cases at any rate, and — equally probably — precociously de- 

 veloped. Now, in no instance is this occurrence known in 

 the Coccidia as a primitive condition. But we do find it 

 now and then (see above, p. 74) as a quite secondary 

 condition,^ acqui red later and independently. That 

 is to say, in spite of the extreme specialisation of the sexual 

 process, which (as Minchin, loc . cit., points out) is entirely 

 to facilitate sexual reproduction, rendered difficult by the 

 intra-cellular habitat and non-motile condition of the para- 

 sites, certain forms have found it profitable to associate pre- 

 cociously, thus insuring fertilisation and allowing of an 

 economy to be effected in the number of (male) gametes. 



We see, therefore that in this closely allied order no 

 support is to be found for the theory that the separate forma- 

 tion of anisogamous gametes is derived from a condition of 

 association and the formation of isogamous gametes. 



One or two other points may be briefly noted. Anisogamy 

 is only known to a marked extent in intestinal forms. The 

 ancestral Gregarine was, in all probability, an intestinal 

 form, from which the ccelomic parasites have been derived. 

 As we have seen, the latter are modified by the greater 



' In tlie few cases where association is met with there is only one niegaga- 

 mete formed as in the other Coccidia ; in these forms, moreover, and only iu 

 these, we find few (often four) microgametes developed. Schaudiiin's work 

 on Cyclospora (see p. 71) teuds to show, however, that the original condi- 

 tion in this order also was the productiou of many female gametes. If, there- 

 fore, association iuAdelea mesnili, etc., was a [)riniiLive character, there 

 would be, in all probability, many female (and, of course, male) gametes. 

 VOL. 50, I'AliT 1. — NEW SERIES. 6 



