1902.] CONKLIN — EMBRYOLOGY OF A BRACHIOPOD. 67 



or the brachiopod larva. It is possible that the ciliated disk of 

 Pedicellina and Loxosoma is homologous with the retractile disk of 

 the ectoproct larva and with the apical plate of the trochophore, 

 and that the margin of the vestibule (ciliated ring) in the former 

 corresponds to the trochus of the latter, but these possible homol- 

 ogies are too hypothetical to be affirmed with any degree of 

 assurance. 



5. Conclusions. — Neglecting the older views as to the affinities of 

 the brachiopods with lamellibranchiate Mollusca, which were 

 founded merely upon superficial resemblances, we find that within 

 recent times the brachiopods have been associated, at different 

 times and by different authors, with Chaetopoda, Polyzoa, Chce- 

 tognatha and Phoronis. 



Both Morse ('73') and Kowalevsky ('74) independently reached 

 the conclusion that the brachiopods are chaetopod annelids. Morse 

 says in summing up his work on the subject ('73', p. 57): "We 

 must regard the brachiopods as ancient cephalized chcetopods, while 

 Serpula, Amphitrite, Sabella, Protula and others may be regarded 

 as modern (later) cephalized chcBtopods''; and Kowalevsky ('74) 

 maintained that the brachiopods ought to be considered simply as 

 an order of the annelids, which present at least as many resem- 

 blances to the chaetopods as do the leeches. 



Morse has enumerated twenty-four characteristics in which brachi- 

 opods resemble more or less closely Vermes, sedentary annelids and 

 Gephyreans. Kowalevsky also names a considerable number of 

 points in which brachiopods resemble chaetopods. Some of these 

 features are not actually characteristic of the brachiopods, as, for 

 example, the segmentation of the larva ; others are of such a gen- 

 eral character as to apply to almost all Bilateralia, as Brooks has 

 shown, while still others represent real resemblances betv/een the 

 brachiopod larva and the trochophore. The trochophore larva 

 however is of such wide occurrence among bilateral animals, that 

 the mere classification of the brachiopods among the Trochozoa 

 throws no light upon the nearer affinities of this group. 



Huxley, Lankester, Claus and others have regarded the brachio- 

 pods as more or less closely related to the Polyzoa, and Brooks in 

 particular has held that the two groups belong to the same phylum 

 and class. ''The organization of the Lingula larva," he says, 

 "shows that it is not merely like a Polyzoon, but that it actually is 

 one; as much so as the hydra stage of an Hydro-Medusa is a 



