PTEROPODA. 



179 



on each side, so that the lateral fissures of 

 the shell have apparently the function of 

 admitting the surrounding element to the 

 branchial organs. These latter are composed 

 of little laminae, resembling those of patellae, 

 phyllidia, &c., which surround the body so as 

 to form a sort of elliptical belt, not placed 

 transversely, but parallel to the course of the 

 dorsal surface (/g. 1 14. 5, 6. p, q, r, s). The 



Fig. 114 (1 to 9). 



Anatomy of Hyalea. {After CWer.) 



1. The animal entire, with its shell, viewed from 

 the side of the inflated valve. 



2. The same seen from the side of the flat valve. 



3. The Hyalea deprived of its shell, the lobes of 

 the mantle drawn aside and expanded, from the in- 

 flated side. 



4. The same from the flat side, in which part of 

 the viscera maybe observed through the membrane 

 of the mantle, as also the muscular fibre of the latter. 



if! 



12 



5. The animal slightly magnified, with the mantle 

 opened from the flat side, showing the retractor 

 muscle and the viscera in situ. 



6. The same, with the viscera displayed. 



7. The same, seen from the opposite aspect : the 

 integument of the neck has been divided as far as 

 the mouth, showing the respective positions of the 

 brain, of the oesophagus, of the penis, and the tongue r 

 like terminations of the retractor muscle. 



y 



8. The penis detached. 



The crop and gizzard laid open. 



The same references apply to all the figures. 



a, b, c, prominent points of shell ; d, inflated valve ; 

 e,f, lateral margins of the shell ; g, h, i, k, margins 

 of mantle ; /, m, cervical fins ; n, mouth ; o, neck ; 

 p, q, r, s, branchiae ; t, position of the heart ; u, re- 

 tractor muscle ; v, v, oesophagus ; w, crop ; x, giz- 

 zard ; y, intestine ; z, liver ; , ovary ; p, testicle ; 

 y, supra-cesophageal ganglion. 



other viscera occupy the arched and rounded 

 portion of the shell, or the interior of the 

 cervical region, and are enveloped in a kind 

 of peritoneum of a blackish colour. On plac- 

 ing the animal upon its flat valve, or ventral 

 surface, the heart is seen to be situated on the 

 right side, at the inner border of that portion 

 of the branchial band marked t in fig. 1 14. 5. 

 A cylindrical muscle (u, Jig. 114. 5 and 7) is 

 attached to the intermediate point of the shell, 

 and traverses the visceral mass to be inserted 

 into the neck by four tongue-like processes. 

 The action of this muscle will be to retract 

 the creature within its shell. 



In front of the four branchias is situated 

 the penis, upon which lies the oesophagus, and 

 this in turn is surmounted by the brain these 

 organs filling up the thickness of the neck. 

 The resophagus (v,i\Jig. 1 14. 5 and 6) is long 

 and slender, and the mouth, according to 

 Cuvier, is a simple anterior opening, in the 

 interior of which a few wrinkles only are 

 perceptible, representing the tongue. The 

 oesophagus dilates into a kind of membranous 

 crop {w, w,fig. 114. 7 and 9), which is suc- 

 ceeded by a muscular gizzard (x,x,jig. 114. 7 

 and 9) of a cylindrical shape, the walls of 

 which are of tolerable thickness. Both 

 these cavities are furnished internally with 

 longitudinal folds, and these are thicker and 

 more numerous in the crop than in the gizzard 

 (Jig. 114. 9). The intestine (y,y,) is slender, 

 and of the same diameter throughout its whole 

 length, which is considerable. It makes two 

 convolutions in the interval between the lobes 

 of the liver (z z, Jig. 1 14. 7). The anus is situ- 



N 2 



