CONTRIBUTIONS TO THE ANATOMY OF THE BRACHIOPODA 333 



but I did not observe in Rhynchonella those accessory vesicles 

 ■upon the origins of genital bands, which I observed once or twice in 

 Waldheimia. 



I could find no trace of arteries terminating the elongated, ovoid 

 and nearly straight ' ventricles ' of Rhynchonella ; their ends appeared 

 truncated, and as I have already said, repeatedly presented a distinct 

 ■external aperture. 



Such appear to me to be the facts respecting the structure of the 

 so-called hearts in the Terebratulidce ; what I believe to be an import- 

 ant part of their peripheral circulatory system, has not hitherto so 

 far as I am aware, received any notice. 



In Waldheimia the membranous walls of the body, the parieto- 

 intestinal bands and the mantle, present a very peculiar structure ; 

 they consist of an outer and an inner epithelial layer, of two corre- 

 sponding fibrous layers, and between them of a reticulated tissue, 

 -which makes up the principal thickness of the layer, and in which 

 the nerves and great sinuses are imbedded. 



The trabeculae of this reticulated tissue contain granules and cell- 

 like bodies, and I imagined them at first to represent a fibro-cellular 

 network, the interspaces of which I conceived were very probably 

 sinuses. Sheaths of this tissue were particularly conspicuous along 

 the nerves. On examining the arms, however, I found that the oblique 

 ■markings, which have given rise to the supposition that they are 

 surrounded by muscular bands, proceeded from trabecule of a similar 

 -Structure, which took a curved course from a canal which lies at 

 the base of the cirri (not the great canal of the arms, of course) 

 round the outer convexity of the arm, and terminated by breaking 

 up into a network. These trabeculae, however, were not solid but 

 hollow, and the interspaces between them were solid. The network 

 into which they broke up was formed by distinct canals, and then, 

 after uniting with two or three straight narrow canals which ran 

 along the outer convexity of the arm close to its junction with the 

 interbrachial fold, appeared to become connected with a similar 

 system of reticulated canals which occupied the thickness of that 

 fold. 



It was the examination of the interbrachial fold, in fact, which 

 first convinced me that these reticulated trabeculae were canals ; for 

 it is perfectly clear that vessels or channels of some kind must sup- 

 ply the proportionally enormous mass of the united arms with their 

 nutritive material, and it is so easy to make thin sections of this part, 

 that I can say quite definitely that no other system of canals than 

 these exists in this locality. 



