162 



ANIMAL PHYSIOLOGY. 



[LESSON 47. 



FIG. 261. 



FIG. 262. 



707. In the Hyalfea (Fig. 261), the head (a) and fins (b, I) form 

 together a large division of the body ; the portion containing the 

 viscera, and which is lodged in the shell (c), constitutes the abdomen. 



708. The mouth is a 

 small longitudinal fis- 

 sure (a, Fig. 262) at 

 the apex of two diverg- 

 ing eminences; it con- 

 tains a tongue covered 

 with a thin, horny plate. 

 There are no salivary 

 Hyalaea, in its shell Nutrimental^-gans glands in this species, 



but they are found well 



developed in the Clio. In both these animals the narrow lengthened 

 03sophagus, which passes under a broad crerebral ganglion (g), and 

 dilates in the abdominal cavity into a membranous crop (6), is 

 slightly marked internally with longitudinal plicae (folds). This first 

 digestive cavity opens directly into a short cylindrical muscular giz- 

 zard (c), likewise marked with longitudinal folds on its inner surface, 

 and lying, like the crop, over the great retractor muscle (&), by 

 which the animal draws its head and fins (t, i) into its shell. From 

 the muscular gizzard, the long narrow intestine (d, e,f) makes a 

 double turn round the lobes of a small liver, and continues nearly of 

 uniform thickness to its termination on the right side of the neck, 

 under the right branchial fin. 



LESSON XLY1I. 



NUTRITION IN THE GASTEROPODA, AND CEPHALOPODA. 



709. In the lower Gasteropods, the respiratory organs are ex- 

 posed, some on the back (Eolis), or the sides of the back ; some at 

 the lower part of the body, between the foot and the mantle ; and 

 some around the body, as in the patella (Limpet). 



710. A figure is given of Eolis Inca (Fig. 263), in which the 

 back is nearly covered with a series of respiratory sacs. 



711. The greater variety in the food, and habits of life of the 

 Gasteropodous Mollusca, renders a more complicated and varied 

 form of the nutrimental organs essentially necessary. Thus, the 



