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 alleged to exist between the 

 Brachiopoda and the Polyzoa, and Hancock, in his masterly 

 works Oil the A^iatomy of the Fresh-water Bryozoa (^Polyzoa) 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 dis- 

 carded group of Molluscoidea. 



In 1854 Huxley^ published what is, with the possible ex- 

 ception 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, after- 

 wards 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. Miiller 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 Bem- 

 melen,2 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 

 views 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, 



1 " Contributions to the Anatomy of the Brachiopoda," Proc. Boy. Soc, vol. vii. 



2 " Uutersuchungen uberden anatomischen u. histologischen Bau der Brachio- 

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



VOL. Ill 2H 



