On the Structure and Development of Argiops. 515 



the fact that the lophophore is prae-oral in Polyzoa and post-oral in 

 Brachiopoda ; and (2; by the fact that the concave side of the lopho- 

 phore is turned in nearly opposite directious in the tveo forms«. The 

 abstractors of Kowalevsky's article in the Archives de Zoologie are at 

 some pains to show that Balfour's statement concerning the Situation 

 of the lophophore is incorrect. Balfour surmises that the ring of ten- 

 tacles forming the lophophore «is possibly derived from the ciliated ring« 

 of the larva, since he considers that the origin as stated Kowalevsky« 

 does not fit in with the aduit anatomy of the parts. It is difficult to 

 understand how the lophophore does grow down over the body, but Ko- 

 walevsky's Observation on the Testicardines are in a measure supported 

 by those of Brooks upon Lingula, who states that in a stage with eleven 

 teutacles the piane of the lophophore is stili almost parallel with that of 

 the mantle lobes. Balfour acting upon bis supposition states that the 

 lophophore is post-oral , and although bis idea as to the origin is incor- 

 rect stili the lophophore remaius a post-oral structure in as much as it is 

 derived from a part of the body which is developed behind the mouth, 

 although it subsequently turns forward. 



With regard to the larvai resemblances, there seem to be no points 

 in common between the two classes^ which they do not also possess in 

 common with some other groups. 



If we compare a free swimming Brachiopod larva with a free swim- 

 ming Polyzoon larva, such asHATSCHEK has figured in bis development 

 of Pedicellina, which is probably more primitive than that of an Ecto- 

 proctous form , we see that almost the ouly point of resemblance is the 

 ciliated ring which occurs so widely amongst free swimming larvae. 

 While the organs in which the respective larvae differ are numerous and 

 striking, in one case the alimentary canal is curved and provided with 

 mouth and anus which both open within the ciliated ring , in the other 

 case it is straight without mouth or anus ; again in the Polyzoon larva 

 there is a well developed pair of excretory organs, in the Brachiopod 

 there are none; then there is the hypothetical »dorsal organ« which 

 Hatschek suggests is a bud, and which has no parallel in the Brachio- 

 pod larva ; finally the Polyzoon larvae become fixed by their prae-oral 

 extremity, the Brachiopods by their aboral extremity ^. 



Van Bemmelen who is the first observer to study the structure of 

 Brachiopods by modem methods , and whose article has been so fre- 



^ J. Barrois. Métamorphoses des Biyozoaires. Annales des Sciences Natu- 

 relles, Zoologie. T. IX. 1879—80. 



