GANYMEDES ANASPIDIS (nOV. GEN., NOV. SP.). 171 



In the first place, the ball and the cavity containing the 

 secreted fluid represent with great probability an epimerite 

 and protomerite. True, there is no cuticular septum; but 

 the secreting tissue forms a fairly definite barrier between 

 these on one side, and on the other the deutomeritic posterior 

 part. Here alone, it is to be remarked, do we find the true 

 granular endoplasm. Occasionally, too, this latter can be 

 seen ending off with a definite contour within the secreting 

 tissue (fig. 3). The ball itself, when extruded, would pass 

 for a typical epimerite save for the absence of a septum 

 behind it ; but in so far as it is protrusible, it is only paralleled 

 by the anterior extremity of Lankesteria ascidise (Sied- 

 lecki, 4). This, however, seems to be mei'ely a pseudo- 

 podium, or a drop of the hyaline inter^reticular substance of 

 the cytoplasm pressed out through a hole by contraction of 

 the animal, and its extrusibility has obviously been inde- 

 pendently evolved. 



The fact of its being a parasite of the digestive tract is the 

 second link with the Polycystidea. The only Monocystid 

 gut-parasite whose life-history has been thoroughly worked 

 out is Lankesteria, and this possesses an '^ epimeritic " 

 oi'gan. The three or four other genera of this sub-class that 

 live in the gut, such as Callyntrochlamy s and Ancora, 

 are very insufficiently known ; it is even possible that they 

 may be Polycystid in early stages. 



Regarding the matter phylogenetically, we find that the 

 early Eugregarine stock must have been motile, Polycystid 

 gut-parasites ; their association was by dissimilar ends, and 

 took place only at the very end of the trophic period ; and 

 they showed well-marked anisogamy. 



One of the first steps towards the typical Monocystid 

 condition was the change of habitat, due very likely in the 

 first instance to the evagination of the full-grown tropho- 

 zoites from the gut into the coelom — as takes place to-day 

 in certain insect-parasites at the time of the host's meta- 

 morphosis. For a full discussion of the further stages, 

 leading eventually to complete isogamy, coupled with entirely 



