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Show 974 PROF. OWEN ON THE SHELLS OF CEPHALOPODS. [Nov. 19, body of the embryo through the narrow aperture thus made " **« The difficulty merely depended upon the " time of the making" the communicating aperture so narrow. A true " embryology" of the Tetrabranchiates will be the welcome result and reward of the fortunate and equal student of the living Nautilus and Spirula, on the shores or in the seas they still frequent, or in the aquarium adapted to conserve and exhibit the male and female of these representatives of the almost extinct order. I cannot conclude the present paper without expressing the pleasure with which may be confidently expected the determination of important points in the physiology of the Tetrabranchiate and Dibranchiate constructors of chambered and siphonated shells by observations made on the living specimens, under the favourable opportunities afforded by their capture to the accomplished Naturalists of H.M.S. 'Challenger,' whose attention had no doubt been directed to the following needful observations and experiments suggested in previous works on the subject. " It would be advisable in the event of another fortunate capture of the Nautilus, to lay open the chambers under water, when the presence of gas in any of them would be ascertained ; and it might be received and analyzed ; the contents also of the central tube, if gaseous, would at once be detected " 2. Prof. Vrolik records similar appeals on more than one point in the structure and physiology of the constructor of the chambered shell. " M . Owen a eu raison de dire que l'orifice h (pl. ii. fig. 2) est en communication avec le pericarde."..."D'apres ce que j'ai vu, le siphon s'ouvre dans la cavite abdomiuale, comme la pl. i. fig. 5, c, le de-rnontre, et dans laquelle j'indique aussi la communication entre la cavite branchiale et le pericarde en d, et entre celui-ci et la cavite abdomiuale ou splanchnique en e."..."En ouvrant la paroi posterieure du pericarde, je me suis assure qu'au fond de celui-ci il y a une ouverture, que M. Owen a deja reconnue, et dans laquelle penetre une petite artere (pl. i. fig. 2, I). Cette ouverture est mise en rapport, pres de l'ovaire et du gesier, avec la cavite abdomiuale." With regard to the course of sea-water from the branchial to the pericardial or peritoneal cavity and thence to the cavity of the siphon, or the reverse course, Vrolik appeals to the fortunate possessors of the living Nautilus : - " L'observation directe seule pourrait les decider" 3. And again, in regard to the circulation, especially of the venous blood :-"Serait-il possible que le sang veineux du canal intestinal fut verse dans ces interstices ou dans ces lacunes, pour passer plus tard, par les orifices cites, dans la veine cave ; et le sang veineux des autres 1 Op. cit. p. 74. 2 Memoir on the Nautilus pompilius, 4to, 1832, p. 47. The same might be urged in the case of the capture of a living Spirula. a " Sur quelques points de l'organisation de l'animal du Nautile Flambe." Memoires de la Societe Linneenne de Normandie, torn. x. (1835), p. 7, pis. i. and ii. |