On the Mechanism of Aquatic Respiration. 247 



specimens of it were sent to Dr. Grenier, and that he called it 

 the E. tetragonum of the ' Flore de France/ In that determina- 

 tion he was assuredly in error, for the plant can belong to no 

 other species described in that admirable work than E.palustre 

 or E.virgatum (the E. obscurum of this paper). In obtaining 

 and quoting the opinion of either of the authors of that ' Flora/ 

 it should be remembered that, although the work is a joint pro- 

 duction, each portion has its own individual and declared author. 

 Dr. Godron is the author of the account of the genus Epilobium. 

 In such cases as this, Dr. Grenier may know no more than the 

 inquirer about the subject upon which he is consulted. 



[To be continued.] 



XX. — On the Mechanism of Aquatic Respiration and on the 

 Structure of the Organs of Breathing in Invertebrate Animals. 

 By Thomas Williams, M.D. Lond., F.L.S., Physician to the 

 Swansea Infirmary. 



[Continued from p. 154.] 



The Glands contained in the Respiratory Cavity of Branchiferous 

 and Pulmoniferous Gasteropods. 



The respiratory cavity of all Cephalophorous Mollusks, in 

 addition to the organs of breathing, lodges one, two or more 

 glandular bodies, the structure and office of which are the subject 

 even at the present time of dispute among comparative anato- 

 mists. In difi'erent genera these glands affect different relative 

 positions in the cavity. 



In some instances they are near and parallel to the rectum, 

 in others they encircle the heart, in others they constitute a 

 mass lying only on one side of this organ. Many of the Pecti- 

 nibranchs are provided with two glands, in the space between 

 which on the roof the branchia is situated. 



By Cuvier they were called the muciparous glands. Dr. 

 Sharpey has supposed the one to be a supplementary branchia, 

 the other he has designated after Cuvier the mucous gland. By 

 Swammerdam, Poli, Blumenbach and the elder anatomists, they 

 were supposed to be concerned in the secretion of calcareous 

 salts. Bojanus conceived that the glands contained in the 

 breathing-chamber of the higher Gasteropods were homologous 

 with certain glandular bodies described by him in the Lamelli- 

 branchs, in both holding a similar relation to the branchiae. As 

 he had proved the latter to be kidneys, he inferred that the 

 former must be so also. The alleged muciparous glands of the 



