AFFINITIES GASTROTRICHA 23 I 



us that the anus of Eotifers cannot be homologous with that of 

 Annelids, etc., for it is formed outside the area of the blastopore : 

 it is an independent formation, probably due to the coalescence of 

 the originally blind intestine at its extremity with the earlier 

 genito-urinary cloaca. On this view we must change the orienta- 

 tion of the Eotifer, and place it, like a Cuttlefish, mouth down- 

 wards : for " anterior and posterior " we must substitute oral (or 

 basal) and apical ; for " dorsal " and " ventral " we must use 

 anterior and posterior ; while " right " and " left " are unchanged. 

 And this correctly expresses the actual space-relations in those 

 Ploima like Battulus that swim with their disc in contact with 

 the organic debris on which they feed, with the foot turned out- 

 wards and backwards. As these views are now published for the 

 first time, I have thought it wiser to keep to the accepted rela- 

 tions in the general description, a course which has the advantage 

 of avoiding difficulties in the study of the literature of the Class. 



The supposed resemblance of Pedalion to the Crustacea is 

 probably the result of convergence, not of consanguinity. The 

 Polyzoa are a group of freely-budding organisms whose structure 

 otherwise recalls in many respects that of the attached Eotifers ; 

 but a close investigation reveals so many differences in structure, 

 orientation, and development, that we cannot regard the two 

 groups as at all closely allied. 



Thus the Eotifers may be regarded as a group apart, but prob- 

 ably representing an early offshoot from a free-swimming Platy- 

 helminth, probably a Ehabdocoele ; the modifications being the 

 loss of the general ciliation of the surface, the arching of the 

 back into an elongated vault, the conversion of the inner half of 

 the pharynx into a gizzard, the change of position of the genital 

 and urinary apertures to the antero- dorsal surface, and the 

 opening of the intestine into the genito-urinary cloaca. 



Gastrotricha. 



This small and very homogeneous group consists of minute 

 fresh-water organisms, closely resembling many Ciliate Infusoria 

 in their movements, habit and habitat. They were first described 

 in detail by Ehrenberg, and placed by him and Dujardin in 

 the neighbourhood of Eotifers. In recent years A. C. Stokes l 

 1 The Microscope (Detroit), 1887-88. 



