238 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



a small artery supplies the siiius in the connective tissue 

 surrounding the nerve. This may at first be mistaken for a 

 branch of the nerve. 



4. A large nerve to the salivary gland and oesophagus. 

 This nerve runs inwards. On the right side the nerves to 

 salivary gland (r. sal. n.) and alimentary canal (r. oes. n.) 

 arise separately as two distinct nerves. The nerve to the gut 

 runs parallel to the oesophagus and branches into two. One 

 branch rims forward again to the pharyngeal crest of the buccal 

 mass, internal to the salivary gland ; the other branch runs 

 backwards along the oesophagus, giving off twigs to it. With 

 its fellow nerve it forms an anastomosing network, which, 

 according to Mazzarelli, accompanies the gut to the anus. 

 Nerve rincrs occur at the level of the gizzard. On the left 

 side the nerve (I. sal. oes. n.) branches into three. One branch 

 goes to the salivary gland, another forwards to the pharyngeal 

 crest, and the third backwards along the oesophagus. 



SENSE ORGANS. 



The sense organs in Ajrtysia consist of paired eyes, paired 

 " Gtocysts," and a single osphradium. In addition there are 

 scattered sensory cells in the epithelium of various parts of the 

 body, particularly on the two pairs of tentacles. The sense 

 of touch is present over the whole outer surface, but is 

 especially acute in the tentacles. Taste is located in the 

 epithelium lining the entrance to the buccal cavity. The 

 rhinophores are the seat of the olfactory sense, but the osphra- 

 dium, which tests the water passing over the ctenidium, must 

 also be said to have some appreciation of odours. The 

 " otocysts " function as organs of orientation and the eyes are 

 the organs of sight. 



The Epithelial Sense Cells. 



On the inner sensory surface of both pairs of tentacles 

 and on the floor of the mantle cavity, roof of the mantle 



