The anatomy of Lottia gigantea Gray. U 



wise plications on these greater folds are also to be seen. The lesser 

 fold of the oesophagus begins as two ridges at either side of the 

 opening of the radula tube (Vf Fig. 2). These converge, and at the 

 posterior end of the pharyngeal cavity unite to form a single fold 

 with two free edges, which, like those of the greater lamellae, turn 

 back. The width of the lesser fold is scarcely a fifth that of the 

 greater. This ventral fold follows a course exactly on the opposite 

 side of the oesophagus from the other, and as shown by Fig. 6 comes 

 to lie on the dorsal and finally on the right side of the oesophagus, 

 ending like the other, after completing a turn of nearly 270 degrees. 

 The epithelium covering both the greater and lesser folds is composed 

 of high ciliated cells with numerous interstitial gland cells which stain 

 deeply with haematoxylin. These cells have the same structure as 

 the mucous cells opening into the buccal cavity, as described above, 

 except that the long slender neck is wanting. The mucous cells pass 

 into these interstitial cells of the oesophageal folds by degrees, from 

 a shortening of the long tube and a gradual lessening in size. In the 

 connective tissue between the two layers of each fold is a blood sinus, 

 which communicates with the network of sinuses in the connective 

 tissue and muscular covering of the oesophagus, and these in turn 

 with a special oesophageal artery, with the visceral artery, and also 

 with the blood sinus of the head cavity. 



Between the greater and lesser folds, the lateral walls of the 

 pharynx are thrown into pockets as before mentioned. These pockets 

 become smaller posteriorly and with the commencement of the oeso- 

 phagus proper are mere spaces between close-lying folds, whose re- 

 lations with the others can be readily made out in Fig. 2. These 

 also end with the proventriculus, and are covered with cylindrical 

 epithelium, the gland cells being scarce or absent. 



There are two paired glands in the oral region of the alimentary 

 canal. The anterior or buccal gland is really situated behind the 

 posterior or pharyngeal gland, but opens by a long glandular duct, 

 into the oral cavity on a dorso-lateral fold, above the palps (Fig. 2 

 Bg, Bg.D, Bg.D', also Figs. 1 and 6), and is hence counted first. 

 This pair of glands might easily be overlooked in dissection because 

 they are very inconspicuous. It is only the ducts that afford a good 

 landmark. But in fresh unhardened specimens they appear white, and 

 hence are easily seen. The buccal gland of the right side is spread 

 out over the septum which separates the head cavity from the viscera, 

 in a thin layer, and dorsally mingled with connective tissue extends 



