BRACHIOPODA. 495 



and are situated In the Ter. flavescens, at the back part of the 

 visceral cavity, on the dorsal aspect of the intestine, one on each 

 side of its upper or anterior half. If the dorsal valve and corre- 

 sponding lobe of the mantle be removed, and the " musculi retractores 

 superiores" be gently divaricated, or the mesial fasciculi carefully 

 removed, the delicate membrane of the venous sinuses, continued 

 from the margin of the basaV aperture of each auricle, is immediately 

 exposed, and is so transparent as to permit the plicated structure of 

 those cavities to be clearly seen.* If the viscera be exposed by a 

 side view, as m Jig. 186, the heart (r, s) of the side exposed will be 

 seen behind the beginning of the intestine. 



The ventricle in each heart is a smooth, feebly- muscular cavity, 

 from which are continued what have appeared to me to be arteries |; 

 the largest ramified on the two halves of the mantle lobes nearest 

 the ventricle, the smaller one proceeding to the viscera and muscles. 



The auricular cavity consists at the half next the ventricle of a 

 plicated muscular coat, in addition to the membranous one ; but 

 at the other half, next the venous sinuses, of venous membrane 

 only : the latter might be termed the auricular sinus, the former 

 the auricle proper. The proper auricle presents the form of an 



" simple, thin-coated, pyriform sacs." " Es sind einfacke dunnhautige, birn- 

 formige Sacke." Vogt subsequently (" Zoologische Bi-iefe," 1851, yoI. i. p. 285) 

 recognised the auricular character of the part, in Lingula, which is so described 

 in Terebratula (CCQll. 1845, p. •>92). 



Mr. Huxley, who erroneously, as he afterwards acknowledged, ascribed this 

 discovery to Vogt, specifies it as " the true complex structure of the heart." 

 (CCCIX. p. Hi.) 



* CCCIII. pi. iii. 1,1. 



f The best demonstration I have been able to make of the vascular system is 

 that shown in the injected preparations 998 A and B (X. vol. ii. p. 74), and more 

 particularly described in CCC I. (1835), p. 154. "In one of the specimens (of 

 Orbicula) I succeeded in injecting the vessels of one lobe of the mantle from one 

 of the ventricles ; in this injected preparation there evidently appeared a small 

 uninjected line {n' fig. 13), as in the Terebratulce, accompanying each of the larger 

 branchial veins, running along the centre of every trunk ; and these lines I con- 

 clude to be branchial arteries ; if they were retractile muscles of the mantle, tht-y 

 might be expected to have a straighter course." 



If it be true that Mr. Hancock has " arrived at the conclusion that no such 

 arteries exist" (CCCIX. p. 112) in the sense that the ramified filaments above 

 described have no existence, I feel no doubt that renewed examination by that 

 excellent observer will convince him of the accuracy of my descriptions and 

 figures (CCCL pi. 22, fig. 11, pi. 23, fig. 11.) The interpretation of the nature 

 of the parts is another matter. Vogt adopts my original idea. He figures the 

 homologous part (CCCVIII. tab. ii. fig. 14. b) as a ' blutgefass.' In all my me- 

 moirs I have called attention to the relation of the generative parts to the pallial 

 vessels, and I have figured the ovaria as being developed from the so-called 

 arteries, in CCCIII. pi. 2, fig. 2, 11. 



