488 MR. P. GEDDES ON THE MECHANISM 
that the radula in Buccinum has muscular attachments, both dorsal and ventral (figs. 24 
& 28), to the cartilages over which it is bent, has argued that the radula “travels over the 
ends of the cartilages just like a band over its pulley, the cartilages being entirely passive 
in the matter,’ and, further, that “the tongue has the same chain-saw-like mode of 
operation throughout Cephalopoda and Gasteropoda.” The anatomical facts, however, 
above described appear to me to render these propositions, on the whole, no longer 
tenable, though an observation remains. In the transparent bodies of some Heteropoda, 
Prof. Huxley! describes a chain-saw movement; so, if the framework remains quite 
stationary, I can only suggest that the sliding of the radula over its support, which we 
saw as a secondary factor in the Limpet, though impossible in the Cuttlefish and highly 
improbable in the Whelk, may in these animals have acquired greater importance. 
A remaining argument, however, of high importance in confirming the view here 
taken is the embryological. In developing embryos of Limnea, days before they 
leave the egg, the action of the incipient odontophore may be observed with a low 
power. Neither radula nor muscles are yet to be seen; but the future cartilages rock 
steadily, licking upwards and forwards with deepening sulcus, quite as described above 
in the adult mechanisms of Patella. The fully developed structure in Pulmogasteropods 
has the usual type; and a transverse vertical section, say of the apparatus in the 
common Snail?, is sufficient to prove its use in licking; while in some cases, ¢. g. the 
adult Limnea, this may easily be proved by direct observation. In Aplysia, too, the 
same structure may be observed. 
Though not coming strictly, perhaps, within the limits of the present paper, a by- 
product of the inquiry may here be noted. Dr. Herman Fol* recently published some 
interesting observations upon Ascidians, from which it appears that the endostyle secretes 
an inverted hollow cone of mucus lining the pharynx, which gradually descends into 
the gullet, bearing attached to it the numerous nutritive particles which enter the 
pharynx in currents of water. An odd analogy to this mode of feeding is furnished 
by the small Limnea stagnalis, which, when creeping about, foot uppermost, at the 
surface of the water in a slightly stagnant aquarium, covered here and there with a 
film of resting Bacteria, is wont cautiously to curve the middle of its foot downwards a 
little, thus producing a shallow boat-shaped depression below the surface, but free from 
water. A very active secretion of mucus now commences over the whole surface of 
the foot; and part of the adjacent film of Bacteria is permitted to slide gently down- 
wards into the hollow, over the anterior edge of the foot, which is not depressed enough 
to let any appreciable quantity of water enter as well. When the cup is nearly full 
the mollusc raises its head and laps up the mixture of mucus with Bacteria, &c. in 
large mouthfuls. For such a purpose a tongue is necessary, a chain-saw would be 
unavailable. 
* Loe. cit. 2 Bronn’s ‘ Thier-Reich,’ Malacozoa, plate xcy. 
3 Gegenbaur’s Morphologisches Jahrbuch, Bd. 1. 
