INTERNAL ANATOMY. 323 



In D. agassizi the palatal spines are entirely solid structures, save at the 

 extreme base, where a slight depression exists, so that, while the general external 

 form and surface-configuration is very much the same as that in 1). hasseltii, 

 the internal structure as seen in sections is strikingly different. The presence 

 of palatal spines has been indicated in many of the Aplysiidae but in no case 

 have any details been given concerning their development or structural rela- 

 tions. Bergh (1905, 1907) briefly describes their form and figures them for 

 Dolabella rumphii [= scapula], this being the only reference to them in this genus. 



Immediately behind the radula, on the floor of the pharyngeal bulb was found 

 a small area of spines similar in form to the palatal ones. They are borne at 

 the summit of a transverse crescentic fold, highest in the median line, which 

 measures 2.0 mm. in length by slightly more in width. In the unopened tube 

 this area would be situated just below the posterior free ends of the palatal folds 

 and immediately behind the median groove of the radula. Unfortunately the 

 epithelium of this region was somewhat macerated, so that further details 

 could not be made out. 



Salivary glands. — The saUvary glands have the long strap-shape common 

 in the family. They enter the bulb upon the posterior dorsal surface, the duct 

 continuing forward near the base of the palatal folds, as shown in Plate 9, fig. 7, d, 

 and opening into the cavity above the anterior portion of the radula. The pos- 

 terior end of the right salivary gland loops across below the oesophagus, its 

 tip being attached to the wall of the proventriculus, immediately in front of 

 the masticatory stomach. The tip of the left salivary gland is similarly inserted 

 upon the opposite side, the relations being the same as in Tethys (MacFarland, 

 1909). 



Oesophagus. — The thick-walled oesophagus, succeeding the pharyngeal 

 bulb is relatively short, measuring some 56.0 mm. in total length. At first 

 it is large and roomy, ranging in diameter from 12.0 mm. just behind the 

 bulb to 17.0 mm. at a distance of 27.0 mm. beyond it. From this point the 

 oesophagus rapidly narrows as it passes upward and to the right, reaching its 

 minimum diameter of 7.0 mm. just before it suddenly dilates into the pro- 

 ventriculus. Its mucous fining is thrown into some ten well-defined longitu- 

 dinal folds, from the sides of which numerous minute and short secondary ones 

 arise but quickly die away. The main longitudinal folds cease abruptly at 

 the entrance of the oesophagus into the first division of the gastric apparatus, 

 the proventriculus, or ingluvies. 



Ingluvies and triturating stomach. — The ingluvies is thin-walled and rela- 



