58 



sumed that the valves of Brachiopoda occupy an anterior and pos- 

 terior position in their relations to the animal. Statements are also 

 made to the effect that " Naturalists have very generally failed to find 

 any evidence of bilaterality in their organization," and also that a 

 " fruitful source of trouble has been that Malacologists are acquainted 

 with the arrangement of the valves in Lamellibranchiata before they 

 examine the Brachiopoda, so that they come to consider the latter 

 order with a vague impression that all bivalves must have the shells 

 in a similar relation to the animal." 



Such remarks unfortunately do injustice to the labors of our Mala- 

 cologists, and should be corrected ; for, since the researches of Cuvier, 

 and still later Owen and Hancock, naturalists have never doubted the 

 relative position of the two valves of Brachiopoda, which have been 

 considered to bear a dorsal and ventral position to the animal ; and it 

 will be evident to all that in viewing their relations thus, the lateral 

 symmetry is apparent and plain, though the assertion is made that the 

 feature of bilaterality seems to be altogether wanting when the valves 

 are thus considered. It seems strange that Mr. Shaler should have 

 overlooked the fact that whether we consider the valves dorsal and 

 ventral, or anterior and posterior, precisely the same imaginary line 

 is drawn, and the same identical valves are made. The statement 

 that the valves are before and behind, I believe to be an incorrect 

 interpretation of the true homological relation which the test bears 

 to the animal ; and, furthermore, the manner in which he determines 

 the longitudinal diameter, by passing a plane through the two extrem- 

 ities of the alimentary canal, is, I believe, a misconstruction of these 

 relations. 



For the reasons that the terms dorsal and ventral are indiscrim- 

 inately used in various departments in the animal kingdom, and 

 quite improperly express the regions in mollusca, to which they 

 are generally applied, the dorsal region, which contains the heart, 

 has been designated the Haemal Region, and the ventral region, 

 which embraces the great nerve-centres, has been called the Neural 

 Region. I shall therefore adopt the terms haemal and neural, as they 

 more properly express an idea of the parts intended. 



In order to appi-eciate clearly the true longitudinal diameter of the 

 Brachiopoda, we must consider the various members belonging to the 

 order of Polyzoa, to which, without doubt, they are intimately connect- 

 ed ; and if we would find the longitudinal diameter of Polyzoa, we 

 have only to compare them with the Ascidian Tunicata. G. J. Allman, 

 in his Monograph of the Fresh- Water Polyzoa, published by the Ray 

 Society, has so clearly pointed out the close homologies existing be- 

 tween the Polyzoa and Tunicata, and illustrated them by excellent 

 diagrams, that it would be doing injustice to him were I to attempt a 



