558 PTEROPODA. 



French anatomist pointed out another vesicle (r), which he compared to 

 the bladder (spermaiheca) of Gasteropod Mollusks. The more complete 

 researches of Professor Eschricht have, however, rendered considerable 

 modifications of the above description requisite, inasmuch as that gentle- 

 man has succeeded not only in detecting a testis quite distinct from the 

 ovigerous canal, but also a very complete intromittent apparatus. The 

 testis, in fact, in a fresh specimen is so large as to occupy a great por- 

 tion of the visceral cavity ; and, no doubt, in the individual examined 

 by Cuvier, which had been kept in spirits of wine, it formed a large 

 portion of the mass (fig. 279, i) which he thought to be entirely made 

 up of the liver. The duct from this testis communicates with the re- 

 ceptacle (q) ; so that the glandular canal (&) must be regarded as a part 

 of the oviduct analogous to what has been called the uterus in the 

 Snail. 



(1497.) Another important discovery for which science is indebted 

 to the Danish Professor is that the Clio possesses a long and sin- 

 gularly-formed penis (fig. 277, c, h) , lodged, when retracted, in the 

 interior of the head of the Pteropod, but which, together with the 

 bladder (#), 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. 



(1498.) 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 semitransparent skin (fig. 279, /) of soft texture ; 

 and within this is a second covering (#), thicker than the first, and 

 exhibiting very distinct muscular fibres, principally distributed in a 

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

 animal and make its shape more spherical. 



(1499.) What fills up the space that intervenes between the mus- 

 cular 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. 



(1500.) The other genera included in this class agree in their general 

 form, and in the arrangement of their digestive and reproductive organs, 

 with Olio above described, but present a few important modifications in 

 the disposition of their branchiae, and other minor circumstances. 



(1501.) In Hyalcea the mantle contains a shell composed of two un- 

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

 branchiaB, which are here distinctly recognizable, form a circle of vascular 

 leaflets enclosed in a cavity of the mantle situated between the divisions 

 of the shell, and so disposed that the water has free admission to them 

 through the two lateral fissures of its testaceous defence. 



