524 QASTEKOPODA. 



in the act of seeking food, four tentacula are protruded (fig. 261, c, d), 

 which, besides being exquisitely sensitive organs of touch, carry, at the 

 extremities of the superior pair, two minute but perfect eyes. When 

 the creature is at rest, the tentacula as well as the eyes are retracted 

 into the visceral cavity, by a mechanism hereafter to be noticed. A 

 large proportion of the viscera is enclosed in a turbinated calcareous 

 shell, of sufficient capacity to allow the whole body of the animal to be 

 withdrawn from observation and lodged in its interior. 



(1380.) The mouth is situated upon the under part of the head, and, 

 when widely opened, exhibits a cutting instrument of singular con- 

 trivance. Attached to the upper part of the muscular cavity that con- 

 tains the oral apparatus there is a broad horny plate, the lower edge of 

 which is free, very sharp, and slightly curved, forming, in fact, a knife 

 (fig. 261, /), admirably adapted to divide the leaves and soft parts of 

 vegetables when they are pressed by the action of the lips against its 

 cutting edge. 



(1381.) The floor of the mouth is .provided with a small cartilaginous 

 tongue, covered with delicate transverse striae, and so disposed that by 

 its movements it is well calculated to assist in propelling the food into 

 the oesophagus. 



(1382.) The oesophagus (fig. 264, e') is continued from the muscular 

 cavity (c f ) that encloses the dental plate, and soon dilates into a wide 

 stomachal receptacle (y , r), the posterior portion of which, when in situ, 

 is imbedded among the viscera contained in the shell ; but in the 

 figure all these parts are unfolded and separated from each other. At 

 the termination of the stomach, biliary vessels (c) are inserted, and the 

 intestine commences, the latter being a simple tube (a, e) , intervolved 

 among the masses of the liver, nearly of equal diameter throughout, 

 and presenting internally neither valves nor any other remarkable 

 appearance. Externally the intestine is intimately connected with the 

 lobes of the liver, among which it lies imbedded, by means of a delicate 

 cellulosity and vascular twigs passing from one to the other. The anal 

 aperture (o), when undisturbed by dissection, is placed upon the right 

 side of the neck, in the immediate vicinity of the orifice (fig. 261, e) 

 that leads into the respiratory cavity. 



(1383.) Two sets of auxiliary glands are subservient to digestion, the 

 salivary and the hepatic, both of which are of considerable size. 



(1384.) The salivary glands are semitransparent, and of a whitish 

 colour ; they form two irregular broad ribands, which extend along the 

 sides of the stomach (fig. 264, v), spreading out so as to embrace a con- 

 siderable portion of its extent, and they are occasionally joined together 

 by intercommunicating processes. Two ducts, one derived from each 

 gland, run along the sides of the oesophagus, and open into that canal 

 close to the mouth. 



(1385.) The liver is of large proportionate dimensions, and is made 



