Chap. XV.] 



THE SNAIL. 



297 



distinction between which may readily be seen in a snail that 

 has been drowned in cold or lukewarm water. A thin-walled 

 saccular part (shaded in Fig. 85, B., ren.) will then be distended 

 with water, and its duct running alongside the rectum will be 

 visible for at least the upper part of its course. The other part of 

 the organ is yellowish white and lamellar in structure. Within 

 the lamellae are great numbers of rounded refringent granules. 



The Nerve-collar. Lying over the oesophagus, as shown in 

 Fig. 86, A., are united cerebral ganglia (c. g.). Lying below the 

 oesophagus are two ganglionic masses tolerably close together. Of 



FIG. 86. SNAIL : NERVOUS SYSTEM, EAR, AND EYE. 



A. Dissection to show nerve-collar, its sheath being removed. B. Otocyst, 

 or auditory organ. C. Eye. 



In A. ao. Aorta, aw. Auditory organ, a. t. Anterior tentacle (retracted) 

 "b. g. Buccal ganglion. 6. m. Buccal mass. c. g. Cerebral ganglion. cr. 

 Crop. e. Eye. op. ti. XJptLc nerve, p. t. Posterior tentacle (retracted). 

 pd. g. Pedal ganglion, pi. g. Parieto-splanchnic ganglion, pd. n. Pedal nerve. 

 pl. n. Pallial nerve. v. n'. Visceral nerve. 



In C. co. Cornea. I. Lens. op. n. Optic nerve, r. Retina. 



these the anterior is formed by the fused pedal ganglia (pd. g.), 

 while the posterior is formed by the fused parieto-splanchnic 



