THE SHELL 465 



to certain members of the Chaetopoda, a view which afterwards 

 found its ablest supporter in the American naturalist Morse. 



D'Orbigny seems to have been the first observer who drew 

 attention to the resemblances allecfed to exist between the 

 Brachiopoda and the Polyzoa, and Hancock, in his masterly 

 works On the Anatomy of the Fresh-ivater Bryozoa {Polyzoct) and 

 in his Organisation of the Brachiopoda, dwelt on these resem- 

 blances, and placed the Brachiopoda between the Polyzoa on the 

 one hand and the Ascidians on the other ; a collocation which 

 subsequently resulted in their inclusion in the now discarded 

 group of Molluscoidea. 



In 1854 Huxley^ published what is, with the possible 

 exception of Hancock's monograph, mentioned above, the most 

 important work upon the anatomy of the Brachiopoda with 

 which we are acquainted. He corrected numerous errors of his 

 predecessors and added many new facts to our knowledge of 

 the group. He was the first to describe the true nature of the 

 lateral hearts of Cuvier, and to describe the true heart, afterwards 

 so carefully figured by Hancock. 



A further step was made in 1860 and 1861 by the discovery 

 and description of the larvae of Brachiopoda, by F. Mliller and 

 Lacaze-Duthiers. Since that time we owe what little advance 

 has been made in the embryology of the group to the researches 

 of Morse and of Kowalevsky. 



Modern methods of research — section cutting etc. — were 

 first applied to the group by the Dutch naturalist, van 

 Bemmelen,- from whose admirable historical account of our know- 

 ledge of the group many of the above facts have been gathered. 

 These methods have thrown considerable light upon the histology 

 of the group, but have not added very much to our knowledge of 

 the structure or the affinities of the Brachiopoda. The modern 

 viev/s as to the latter point may be best discussed after some 

 account of the anatomy of the various genera has been given. 



The Shell 



The body of a Brachiopod is enclosed within a bivalve shell, 

 but the two halves are not, as they are in the Pelecypoda, 



^ " ContributioDS to the Anatomy of the Brachiopoda," Proc. Roy. Soe.,vo\. vii. 

 - " Untersuchungen iiber den aiiatomischen u. histologischen Bau der Brachio- 

 poda Testicardinia, " Jenaische Zeitschrift, vol. xvi., 1883. 



VOL. Ill 2 H 



