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
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