CEPHALOPODA. 627 



water is admitted into the branchial cavity at the anterior aperture 

 of the mantle, outside the base of the funnel. Two large valvular 

 folds of fibrous membrane, which are concave towards the respiratory 

 cavity, prevent the currents from escaping by this entry : they are, 

 therefore, propelled by the whole force of the contraction of the 

 muscular mantle through the cavity of the funnel, the base of which 

 is articulated, in most of the Cephalopods, by lateral joints, with the 

 sides of the anterior aperture of the mantle. 



Although the apertures which I first pointed out in the Nautilus, 

 near the base of the gills, ai-e situated on prominences, which seem 

 intended rather to let excretions out than fluids, in, they are regarded 

 by Siebold as being, together with some analogous apertures in the 

 Dibranchiates, parts of an " aquiferous system." This system is 

 described by that usually accurate and sound-judging anatomist* as 

 " occupying the entire trunk of the Cephalopods, and terminating by 

 two orifices, between which lies the duct of the ink-bag, and which 

 are often situated on a small tubular eminence of the peritoneum. 

 Each of these orifices leads to a spacious thin-walled cavity, near the 

 pericardium. It contains the two venae cavae, with their appendages, 

 and communicates by orifices and canals with other aquiferous cavities 

 surrounding the various viscera, as e. g. the stomach and caecum, 

 and the two so-called branchial hearts. There is another system of 

 aquiferous canals under the skin of the head and neck. It consists 

 of several large reservoirs, which extend somewhat deeply between 

 the organs of this portion of the body. These reservoirs commu- 

 nicate externally by orifices situated upon diffierent points of the 

 head." The peritoneal and pericardial orifices in some cartilaginous 

 fishes, and the peritoneal orifices in the crocodile, are the last homo- 

 logous traces of the aquiferous system of the marine invertebrates : 

 but the valvular structure of the orifices is opposed to the idea of 

 their performing a similar function, viz., admitting water into the 

 peritoneal and pericardial cavities. And further research is needed 

 to determine what actually goes in or out of the openings between 

 the branchial and peritoneal cavities in the Cephalopods. 



The Cephalopods are dioecious : the males are fewer, and generally 

 smaller, than the females ; and some species have more definite out- 

 ward sexual characters. 



In a male Nautilus pompilius, V. der Hoevenf found, beneath and 

 external to the internal labial processes, a fold from which a dis- 

 memberment of the right external labial process, consisting of the 

 confluent sheaths of four tentacles, projected. On the left side, in 



♦ XXIV. p. 398. t CCCXC. 



88 2 



