330 CONTRIBUTIONS TO THE ANATOMY OF THE BRACHIOPODA 



which he had already taken of the circulation in Orbicula, I presume 

 that he considers two opposite types of the circulatory organs to ob- 

 tain in the Brachiopoda, the direction of the current -being from the 

 mantle through the heart towards the body in Orbicula, and from the 

 mantle through the body towards the heart in Terebratiila. 



The possibilities of nature are so various that I would not venture, 

 without having carefully dissected Orbicula, — no opportunity of doing 

 which has yet presented itself, — to call this view in question, but I 

 think it seems somewhat improbable. Indeed the structural rela- 

 tions which I have observed and which are described below, do not 

 appear to me to square with any of the received doctrines of Bra- 

 chiopod circulation, but I offer them simply as facts, not being 

 prepared at present to present any safe theory on the subject. 



In Waldheiniia flavescens there are t-wo ' hearts,' situated as Pro- 

 fessor Owen describes them, but so far as I have been able to ob- 

 serve, the ventricle cannot be described as an ' oval ' cavity, inas- 

 much as it is an elongated cavity bent sharply upon itself Hastily 

 examined of course this may appear oval. I have been similarly 

 unable to discover ' the delicate membrane of the venous sinuses,' 

 which is said by Professor Owen to " communicate with and close 

 the basal apertures of the auricles," or to perceive that the auricular 

 cavity can be " correctly described as a closed one, consisting at the 

 half next the ventricle, of a beautifully plicated muscular coat in 

 addition to the membranous one, but at the other half next the venous 

 sinus of venous membrane only ; the latter might be termed the 

 auricular sinus, the former the auricle proper." 



I presume that ' this delicate membrane of the venous sinuses ' 

 is what I have called the ilio-parietal band, in which the base of the 

 auricle is as it were set, like a landing-net in its hoop, but this 

 does 7iot close the base of the auricle, the latter opening widely into 

 the visceral chamber. 



I have equally failed in detecting any arteries continued from the 

 apices of the ventricles ; and I have the less hesitation in supposing 

 I have not overlooked them, as Mr. Albany Hancock, whose works 

 are sufficient evidence of the value of his testimony, permits me to 

 say that he long since arrived at the conclusion that no such arteries 

 exist. 



What has given rise to the notion of the existence of these arteries 

 -appears to me to be this. A narrow band resembling those I have 

 already described, is attached in Waldheimia along the base of the 

 ' ventricle ' and the contiguous outer parietes of the auricle : inferiorly 

 it passes outwards to the sinuses, and running along their inner 



