VIII THE RADULA 21$ 



The carnivorous genera, whether marine (e.g. Conus^ Murex^ 

 Buccinum^ Nassa) or hind (e.g. Testacella^ Q-landina^ Streptaxis, 

 Ennea)^ are entirely destitute of jaws, the reason probably being 

 that in all these cases the teeth of the radula are sufticiently 

 powerful to do the work of tearing up the food without the aid 

 of a masticatory organ as well. Jaws are also wanting in the 

 Heteropoda, and in many of the Nudibranchiata and Tecti- 

 branchiata. 



In the Cephalopoda the jaws, or 'beaks,' as they are called, 

 are most formidable weapons of attack. In shape they closely 

 resemble the beaks of a parrot, but the hook on the dorsal side 

 of the mouth does not, as in birds, close over the lower hook, 

 but fits under it. Powerful muscles govern these mandibles, 

 which must operate with immense effect upon their prey 

 (Fig. 110). 



The Radula} — When the food has passed beyond the opera- 



1 The whole of the radulae and jaws figured in this work are taken from the 

 original specimens in the collection of the Rev. Prof. H. M. Gwatkin, who has 

 always been ready to give me the run of his cabinets, which probably contain 

 the finest series of radulae in the world. To his kindness I owe the following 

 description of the process of mounting: " The first step is to obtain the radula. 

 Dissection is easy in species of a reasonable size. On opening the head from 

 above, so as to lay open the floor of the mouth, the radula itself is seen in most 

 of the marine species, though in others it is contained in a sort of proboscis ; 

 and in the Pulmonata and others the student will find the buccal mass, with 

 commonly a brown mandible at its front end, and the lingual ribbon in its 

 hinder part. The teeth may be recognised by their silvery whiteness, except in 

 a few cases like Patella and Chiton, where they are of a deep brown colour. 

 When obtained, the radula may be cleaned by boiling in a solution of caustic 

 potash. There is no risk of injury if the solution is not too strong. 



"Smaller species may be treated more summarily. The proboscis, the 

 buccal mass, or even the whole animal may be thrown into the potash solution 

 and boiled till scarcely anything is left but the cleaned radula. Remains of 

 animals dried inside the shell may be similarly dealt with, after soaking in clean 

 water. With a little care, this process will answer for shells down to the size 

 of Ancylus or Rissoa. The very smallest (Carychium, Tornatpllina, Sl'enea^ 

 etc.) must be crushed on the slide and boiled on it, after removing as much as 

 possible of the broken shell. The radula can then be searched for under the 

 microscope, and washed and mounted on the slide. 



"The student must be w^arned that though the general process is simple, 

 there are difficulties in particular cases. In the Pulmonata, for example, mem- 

 branes on both sides of the radula need careful removal. M:irex, Purpura, and 

 most of the Taenioglossa have the side teeth folded down over the central, so 

 that the arrangement is not well seen till they have been brushed back. The 

 Cones, again, have no basal membrane at all, so that if the potash is not used 

 with great care, the single teeth will fall asunder and be lost. Perhaps the 

 worst case is where a large animal has a radula as small as that of a Bissoa^ 



