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, f), which unites the posterior ends of the palatal folds across the median 
line, 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-like 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 lighter 
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. asa 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. 
Tn 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 epithelium of slender cells which secrete it. The 
nuclei are small, contain fine chromatin granules scattered on a delicate 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 
