580 CEPHALOPODA. 



by the action of its muscular walls, through a valvular aperture provided 

 for the purpose, and again expelled in powerful streams through the 

 orifice of the funnel. Such, indeed, is the force with which the water 

 is ejaculated through the funnel, that it not only serves to expel from 

 the body excrementitious matter derived from the termination of the 

 rectum (fig. 290, s), which opens into the respiratory cavity, but be- 

 comes one of the ordinary agents in locomotion. This mode of progres- 

 sion, although in fact common to most of the Cephalopod tribes, is re- 

 markably exemplified in the Argonaut, which, instead of navigating the 

 surface of the sea, as has been already stated, simply darts itself from 

 place to place by sudden and oft-repeated jets thus violently spouted 

 forth, while with its arms stretched out and closely approximated, and 

 its vela tightly expanded over the outward surface of its delicate shell, it 

 shoots backwards like an arrow through the water. 



(1553.) Separated from the chamber in which the branchiaB are 

 lodged, by the membranous partition already mentioned (fig. 290, t), and 

 likewise distinct from the peritoneum containing the viscera, is a con- 

 siderable cavity, divided by a membranous partition into two compart- 

 ments, wherein are placed the great trunks of the venous system (d d) . 

 These chambers, named by Cuvier* the " great venous cavities," are 

 very remarkable, inasmuch as, although they contain the venae, cavce, 

 which here present a truly anomalous structure, they are lined with a 

 mucous membrane derived from the branchial chamber, with which they 

 are in free communication, and from whence the external element has 

 free admission to their interior. 



(1554.) It is in this " great venous cavity" called by Professor Owen 

 the "pericardium" that, in the Pearly Nautilus, the siphon which 

 traverses the partitions of its camerated shell (fig. 284) terminates ; 

 and the reader will now perceive by what mechanism water received 

 from the branchial chamber may, in that animal, be injected into its 

 partitioned shell for the purpose already referred to ( 1517). 



(1555.) In the " great venous cavity " or "pericardium" thus formed, 

 are lodged the principal venous trunks (fig. 290, d d), into which the 

 blood derived from all parts of the body is brought by capacious vessels 

 (b, c c) that may be called the vence cavce. The great central receptacles 

 of the venous blood (d d), whilst they are contained in the pericardium 

 (or, rather, project into its interior, being partially covered with the 

 mucous membrane that lines its walls), are enveloped by a mass of 

 spongy appendages of a most remarkable and peculiar description. 

 These spongy masses are of a yellow colour, and, when squeezed, they 

 give out an opake yellowish mucosityf; but the most interesting cir- 

 cumstance connected with these bodies is, that they communicate by 

 large and patulous apertures with the interior of the veins to which 

 they are adherent. The short canals derived from these apertures are 

 * Memoire sur la Poulpe. f Ibid. 



