WOODWAKD : ANATOMY OF PTEROCEEA. 145 



gradually away into a small tube, and is situated, together with the 

 anterior aorta, in a narrow channel-like body-cavity hollowed out of 

 the great anterior musciilar mass of the body ; from this it passes 

 into the coiled visceral mass, and running through the liver becomes 

 slightly funnel-shaped and enters the stomach. 



The structure of the stomach was described by Huxley,' but since my 

 observations differ somewhat from his I append a short description of it. 

 The stomach is a trilobed sac buried in the lower part of the liver and 

 near the right side of the body ; its dorsal border, which we may, for 

 convenience, call the greater curvature, exhibits two well-marked 

 constrictions ; the oesophagus enters the middle chamber on its ventral 

 border or lesser curvature, to the left of which we find the posterior 

 chamber as a small round cardiac sac. The intestine leaves the 

 pyloric portion of the stomach as a very narrow tube, situated just 

 anterior to the cardiac orifice ; this pyloric sac is continued forward, 

 and finally gives off a long c^cal tube which runs through the liver, 

 over the anterior aorta, and, passing close to the left of the pericardium, 

 enters the dorsal mantle wall, down which it extends just to the left 

 of the osjihradium, nearly the whole length of the gill, where it 

 ends abruptly. This ca)cum contains a body having all the structure 

 and relation of the crystalline style of the Lamellibranchiata. The 

 existence of this structure was first pointed out by Collier,'^ and after- 

 wards by Huxley,' and I shall refer to this point later on. 



On opening the stomach, it is seen that the two constrictions 

 are still more marked internally than externally, owing to the 

 development of a couple of sharp ridges of almost cartilaginous 

 nature and tooth-like form ; these thin out on either side on the 

 walls of the sacculations, so that the stomach is almost completely 

 lined by a firm transparent secretion of its lining epithelium, 

 reminding one of the horny lining of a binl's gizzard, the tooth-like 

 structures corresponding in function to the horny plates of that organ. 

 These structures, which are to a large extent protective as well as 

 crushing organs, correspond in every respect to the sagitta or " fleche 

 tricuspide " of the Lamellibranchiata, and, like that tissue, are com- 

 posed of a substance giving reactions very similar to those of mucin. 



Opening into the cardiac sac we find the right bile duct, while the 

 left one opens into the pyloric sac close to the origin of the ciecum. 

 Within the latter structure is the well-developed crystalline style 

 about 4 inches long, tapering away to a point at the blind end of 

 the sac, while its free end, which is broad and flat, projects into the 

 pylorus and abuts against the large anterior tooth-ridge. This free 

 end is of a less homogeueous nature than the rest of the style, and 

 assimilates the appearance of the recently digested food. 



The stomach was full, and its contents show the animal to be a 

 very mixed feeder, plant remains being abundant, especially threads 

 of blue-green algae and brown seaweeds ; in addition there were a 



1 Huxley, Phil. Trans. 1853, pp. 60-61 . 



■^ Ediub. New Pliil. Jouru., vol. vii. 1829, pp. 230-231. 



