3 



THE CEPHALOPODA 



As in the Amphineura, the Gastropoda, and the Scaphopoda, the 

 floor of the buccal cavity is occupied by the anterior part of the 

 radulaj which issues from a pharyngeal caecum. Each transverse 

 series of this radula is formed by a median tooth, with three 

 symmetrically disposed teeth on either side ; the only exceptions 

 to this rule being Nautilus, which has four teeth on either side 

 (Fig. 267, A); Gonatus, which has only two teeth on either side; 

 the Cirrhoteuthidae, which have no radula and have therefore been 

 named Leioglossa. In front of the radular prominence is the 

 so-called "tongue," a fleshy projection (Fig. 268, to) covered by a 



FIG. 267. 



Radula of Cephalopoda. A, a single row of lingual teeth of Nautilus pompilius ; B, two rows 

 of lingual teeth of Sepia officinalis ; C, lingual teeth of Eledone eirrhosa. (From Lankester, 

 after Keferstein, Troschel, and Loven.) 



somewhat thick papillated cuticle : it corresponds to the sub-radular 

 organ of other Molluscs. 



The salivary glands, of which two pairs are present in many 

 Cephalopoda, pour their secretion into the buccal cavity. In 

 Nautilus there are no posterior salivary glands, but on each side of 

 the buccal cavity there is the orifice of a gland situated in the 

 buccal wall and corresponding to the anterior salivary glands of 

 the majority of the Dibranchia. In the latter order all the Decapoda 

 have posterior salivary glands, situated fairly far forward opposite 

 the cephalic cartilage (Fig. 268, s.g) : they are compact, acinous, 

 almond-shaped structures composed of convoluted and bifurcated 

 tubes ; their ducts unite immediately they leave the glands to 

 form a single median duct, which runs alongside of the oesophagus 

 and opens, like the duct of one of the pairs of glands in the 

 Aplacophora, at the summit of the sub-radular organ. The anterior 



