CEPHALOPODA. 



429 



as a part of the oviduct analogous to what has been called the ute- 

 rus in the snail. Figt 2 oo. 



Another important 

 discovery, for which 

 science is indebted to 

 the Danish Professor, 

 is, that the Clio pos- 

 sesses a long and sin- 

 gularly - formed penis 

 (fig. 198, c, A), lodged, 

 when retracted, in the 

 interior of the head of 

 the Pteropod ; but 

 which, together with 

 the bladder (g), in 

 which it was contained, 

 can be extruded from 

 the right side of the 

 neck to such an extent that it nearly equals in length the whole 

 body of the little creature. 



The mass formed by the viscera occupies but a small space in the 

 general cavity of the body. The external investment of the visceral 

 sac is a thin semi-transparent skin (f) of soft texture ; and within 

 this is a second covering (g), thicker than the first, and exhibiting 

 very distinct muscular fibres, principally distributed in a longitu- 

 dinal direction, so that their action would seem to shorten the 

 animal and make its shape more spherical. 



What fills up the space that intervenes between the muscular 

 tunic and the viscera is as yet undetermined ; but Cuvier, in the 

 memoir above referred to, suggests that it may possibly contain air, 

 which, as it should be compressed or allowed to expand, would 

 form a kind of swimming-bladder, and allow the animal to mount 

 to the surface, or sink into the recesses of the sea, with little effort 

 or exertion of muscular power. 



(471.) The other genera included in this class agree in their 

 general form, and in the arrangement of their digestive and repro- 

 ductive organs, with Clio above described ; but present a few im- 

 portant modifications in the disposition of their branchiae, and other 

 minor circumstances. 



In Hyalaa the mantle contains a shell composed of two unequal 

 plates ; one of which is dorsal, and the other ventral : and the 



