THE SNAIL. 57 



PLATE XIII. 



THE SNAIL (Helix aspersa). EXTERNAL CHARACTERS. THE SHELL. THE ALIJIENTAEY, 

 CIRCULATORY, RESPIRATORY, AND EXCRETORY ORGANS. 



FIG. I. The living animal, from the right side. 

 FIG. II. The same, from the front. 



FIG. III. The shell, in median longitudinal section through the columellar axis. The 

 attached ends of the great retractor muscles were left. 



FIG. IV. The hybernaculum (hypophragm), after removal from the shell. 



(Figs. I. to IV. all nat. size.) 



FIG. V.--The alimentary canal, with its appended glands and associated muscles, from 

 the right side. 



On cutting open the pulmonary chamber, dissecting out the rectum and removing the 

 generative organs and nervous system, the parts fall naturally into the positions here 

 figured. 



The stomach and portions of the bile-ducts and intestine have been opened up. x 2. 



The so-called liver of the gasteropod is stated by Barfurth (56) to perform, among 

 other functions, those of a hepato-pancreas. (Compare Astacus, Plate IX., Fig. VI.) 



FIG. VI. The horny jaw, viewed from the front in situ, * 3. 



FIG. VII. Median longitudinal section of the buccal mass and pedal gland, from the 

 right side, x 4. 



Sochaczewer (80) claims for the above gland an olfactory function. 



FIG. VIII. Transverse section across the sac of the radula. x 8. 



FIG. IX. A portion of the radula, magnified. 

 The middle row of teeth has been stippled. A. 2. 



FIGS. X. and XI. The median and first lateral tooth of the right side, in situ. 

 FIG. XII. One of the outer lateral teeth of the same side. D. 2. 



FIG. XIII. Dissection to show the heart, pericardium, and the excretory organ. 



The pulmonary sac was slit open in a line with the respiratory aperture, and the outer 

 wall of the excretoiy organ removed, to show its internal structure. Both the pericardium 

 and he^irt were opened up. x 2. 



8 



