CONTRIBUTIONS TO THE ANATOMY OF THE BRACHIOPODA 33 1 



wall, forms a sort of ridge ar axis ^ from which the genitalia, whether 

 ovaria or testes, are developed, stretching through their whole length 

 and following the ramifications of the sinuses. It is the base of these 

 ridges seen through the walls of these sinuses, where they extend 

 beyond the genitalia, which have been described as arteries. 



The upper end of the band passes into the sinuses of the upper 

 lobe of the mantle, and comes into the same relation with the genitalia 

 which they enclose. 



The walls of the auricle in Waldheimia are curiously plaited, but 

 I have been unable, in either auricle or ventricle, to detect any such 

 arrangement of muscular fibres as that which has been described. 

 The epithelial investment of the auricle, on the other hand, is well 

 developed, and in the ventricle the corresponding inner coat is raised 

 up into rounded villous eminences. 



The ventricle lies in the thickness of the parietes, while the auricle 

 floats in the visceral cavity, supported only by the ilio-parietal band. 

 The former is at first directed downwards, but then bends sharply 

 round and passes upwards to terminate by a truncated extremity 

 close to the suboesophageal ganglion and bases of the arms. 



Mr. Hancock informs me, that in his dissections he repeatedly 

 found an aperture by which the apex of the ' ventricle ' communi- 

 cated with the pallial cavity ; and that, taking this fact in combina- 

 tion with the absence of any arteries leading from this part, he had 

 been tempted to doubt the cardiac nature of these organs altogether, 

 and to regard them rather as connected with the efferent genital 

 system, had not the difficulty of determining whether these aper- 

 tures were artificial or natural prevented his coming to any definite 

 conclusion at all. 



Before becoming acquainted with Mr. Hancock's investigations, I 

 .had repeatedly observed these apertures in Rliynchonella, but pre- 

 occupied with the received views on the subject, I at once inter- 

 preted them as artificial. A knowledge of Mr. Hancock's views, 

 however, led me to reconsider the question, and I have now so 

 .repeatedly observed these apertures both in Waldheimia and in 

 Rhynchonella, that I am strongly inclined to think they may after all 

 be natural. 



If these organs be hearts, in fact, Rhynchonella is the most remark- 

 ■ able of living Mollusks, for it possesses four of them. Two of these 

 ■occupy the same position as in Waldheimia, close to the origins of the 

 calcareous crus (Ji), while the other two are placed above these, and 



1 This arrangement is, I find, particularly described by M. Gratiolet. 



