642 



MOLLUSCOIDEA. 



vesicle situated on the dorsal side of the stomach. The body-cavity 

 proper is filled with a corpusculated fluid, and sends out branched 

 prolongations into the substance of the pallia! lobes. These so- 





Fig. 487. — Anatomy of Waldheimiajlavescens. a, View of the animal after the ventral valve 

 of the shell has been removed, enlarged. B, Longitudinal section, enlarged : d, Spirally-coiled 

 "arm," with lateral cirri (A); a, Adductor muscle; c, c , Divaricator muscles; s, Septum; v, 

 Mouth ; z, Terminal portion of the alimentary canal. (After Davidson.) 



called " pallial sinuses " often leave well-marked branching " vascular 



impressions " on the internal casts of the fossil Brachiopods (fig. 488). 



The central nerve-system of the Brachiopods has the form of a 



Fig. 488. — Internal cast of Rhynchonella acuminata, from the Carboniferous rocks, viewed 

 ventrally and from the umbonal aspect. A, Mark left by the adductor muscle ; r, Cardinal 

 muscular impression; p, Mark left by the peduncle; v, "Vascular impressions"; o, Ovarian 

 impressions. (After Davidson.) 



circum-oesophageal ring, with a large sub-cesophageal ganglion, and 

 sometimes small supra-cesophageal ganglia as well. The sexes are 



