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 Tetrahranchiates 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 fre- 

 quent, 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 

 Dibraucbiate constructors of chambered and siphonated shells by 

 observations made on the living specimens, under the favourable 

 opportunities afforded by their capture to the accomplished Natu- 

 ralists of H.M.S. ' Challenger,' whose attention had no doubt been 

 directed to the following needful observations and experiments sug- 

 gested 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 (pi. ii. fig. 2) est en 

 communication avec le pericarde."..." D'apres ce que j'ai vu, le siphon 

 s'ouvre dans la cavite' abdominale, comme la pi. i. fig. 5, c, le de- 

 montre, et dans laquelle j'indique aussi la communication entre la 

 cavite branchiale et le pericarde en d, et entre celui-ci et la cavite 

 abdominale ou splanchnique en e."..."En ouvrant la paroi posteri- 

 eure 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 peuetre 

 une petite artere (pi. i. fig. 2, /). Cette ouverture est mise en rap- 

 port, pres de l'ovaire et du gesier, avec la cavite abdominale." 



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 de- 

 cider" 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 ftpirula. 



3 " Sur quelques points de l'organisation de l'animal du Nautile Flarabe." 

 JVTimoires de la Societe Linneenne de Normandie, torn. x. (1835), p. 7, pis. i. 

 and ii. 



