INTERNAL ANATOMY. 319 



the inner free ones are thick and fleshy and nearly meet each other in the median 

 plane. Thus they form the incomplete floor of a dorsal space, of a more or less 

 elongated triangular form, limited behind by a low transverse ridge (Plate 8, 

 fig- 5,/), wliich unites the posterior ends of the palatal folds across the median 

 Une, though communicating freely with the oesophagus beyond. This space 

 is the "doccia faringea" of Zuccardi (1890) or pharyngeal groove, and is con- 

 sidered as a prolongation of the dorsal portion of the oesophagus, the palatal 

 folds being his "creste pharynge," or pharyngeal crests. It communicates 

 freely with the cavity above the radula and loses its identity as a separate groove 

 before reaching the region of the upper ends of the mandibles, contrary to the 

 observations of Zuccardi in the Neapolitan Aplysiidae. Into the anterior 

 portion of this space the ducts of the long strap-Uke salivary glands open. 



Palatal spines. — Each of these palatal folds bears thickly set tapering spines 

 on its ventral surface, their tips being directed obliquely backward. The tips 

 are brown or of a deep amber color, while the main portion of the shafts is Ughter 

 amber or whitish. The spines are quite flexible, readily bending on pressure 

 with a needle. In length they range from 0.24 mm. to 0.5 mm., with a basal 

 diameter reaching 0.096 mm. as a maximum. They are gently tapering through- 

 out their extent, with the tip abruptly curved backward, as shown in Plate 9, 

 fig. 1, 8. The surface of each spine is obliquely ridged by a series of parallel 

 elevations, corresponding to strata of growth which extend through its whole 

 thickness. The lower one half to two thirds of the spine bears a moderate, 

 shallow groove upon its posterior surface (Plate 9, fig. 1). Toward the pos- 

 terior border of the palatal fold the spines become more slender and filiform 

 (Plate 10, fig. 9). All the palatal spines are imbedded in a thick chitinous or 

 cuticular matrix, from which the distal ends of the longer spines alone project. 

 In a surface view of a total preparation, isolated with KOH, this matrix is so 

 clear and transparent that it is readily overlooked, the spines appearing entirely 

 free save at their bases, but in transverse sections, as in Plate 9, fig. 7, b., its 

 presence and true nature is evident. Beneath this general cuticular layer is 

 situated a high columnar epitheUum of slender cells which secrete it. The 

 nuclei are small, contain fine chromatin granules scattered on a dehcate linin 

 network, and are situated in the basal half of the cell. The distal half is filled 

 with fine granules, extending down to the zone occupied by the nuclei. Near 

 the anterior border of the palatal flap these granules are especially numerous, 

 and frequent evidence of a discharge of a homogeneous secretion from the cells 

 into the cuticle is seen, Plate 10, fig. 7. This secretion is most marked in the 



