DIGESTIVE ORGANS. 95 



vvdatum by Cuvier and Valenciennes, are probably appendages 

 of the tongue, and used as a handle in perforating the shells 

 on which they pre}'. 



Odontophore. The odontophore or so-called tongue (xi, 22 ; 

 XV, 83) is attached to the floor of the mouth. It is usuall}' 

 curved in front, and its margins rolled together into a cylinder 

 behind, which is supposed to open as the tongue grows forward 

 bringing its rows of teeth successively into use. It contains 

 two parallel cartilages, which may be more or less confluent, and 

 which are united towards the middle by fibrous and muscular 

 tissue. " The intrinsic muscles of the odontophore are attached 

 at one end to the posterior and under faces of the subradular 

 membrane, some being inserted into its posterior and lateral 

 portions, and others into its anterior extremity, after it has 

 turned over the anterior extremities of the principal cartilages. 

 Certain of the muscular bundles are also attached to the forepart 

 of the odontophoral cartilages themselves. The contraction of 

 these muscles must tend to cause the subradular membrane, and 

 with it the radula, to travel backwards and forwards over the 

 ends of the cartilages in the fashion of a chain-saw, and thus to 

 rasp any body against which the teeth may be applied. When 

 undisturbed, the radula is concave from side to side, and the 

 teeth of the lateral series, being perpendicular to the surface to 

 which they are attached, are inclined inwards to one another. 

 But when the intrinsic muscles come into action, the radula, as 

 it passes over the ends of the cartilages, becomes flattened, and 

 the lateral teeth are consequently erected or divaricated. The 

 extrinsic muscles pass from the odontophore to the lateral walls 

 of the head, and protract or retract the whole apparatus. They 

 may give the protruded extremity of the radula a licking motion, 

 which is quite independent of the chain-saw action due to the 

 intrinsic muscles." — Huxley, Anat. Invert., 490.* 



The subradular membrane does not terminate behind with the 

 muscular mass of the tongue, but is continued and invaginated 

 into a pouch called the tongue-sheath. The under wall of the 

 oral cavity forms a muscular elevation, which is frequently semi- 

 circular, and above which the oesophagus opens. Troschel has 

 regarded this as an organ of taste, and from its position it may 

 well have that function. 



The odontophore, radula or lingual plate, is chitinous, subcor- 

 neous, transparent and colorless or yellowish. Its surface is 



* Geddes has recently carefully investiprated the mechanism of the 

 odontophore in Loligo, Buccinum and Patella. He does not altogether 

 agree with Huxley as to the mode of action of this organ, but thinks its 

 movements depend on those of the cartilages, whilst Huxley regards the 

 cartilages as passive. — 7Va?is. Zool. Soo. Lond&n, x, 485, 1879, with three 



