113 



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

 round and passes upwards to terminate by a truncated extremity 

 close to the subcesophageal 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 Rhynchonella, but preoc- 

 cupied with the received views on the subject, I at once interpreted 

 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 (k), while the other two are placed above these, and 

 above the mouth, one on each side of the liver (i). It is these latter 

 which Professor Owen describes, while he has apparently overlooked 

 the other two, at least he says (speaking as I presume of Rhyncho- 

 nella) (I. c. p. 148) that the venous sinuses " enter the two hearts 

 or dilated sinuses which are situated exterior to the liver, and in 

 T. Chilensis and T. Sowerbii just within the origins of the internal 

 calcareous loop." 



The fact is, that while the ilio-parietal bands support two ' hearts ' 

 as usual, the gastro-parietal bands are in relation with two others. 

 The base of the 'auricle' of the latter opens into the re-entering 

 angle formed by the gastro-parietal band with the parietes, while 

 its apex is directed backwards to join the ventricle, which passes 

 downwards and backwards along the posterior edge of the posterior 

 division of the adductor muscle. 



The auricles in Rhynchonella are far smaller, both actually and 



