THE RADULA 2 I 3 



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

 Buccinum, Nassa) or land (e.g. Testoxella, Glandina, Strcptao:is, 

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

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

 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} — -Wlien the food has passed beyond the opera- 



^ 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 descrip- 

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

 is easy in species of a reasonable size. On opening tlie head from above, so as to 

 lay open the floor of the month, 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 recog- 

 nised 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. Pvemains 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 (Carychiuin, Tornatcllina, Skenea, 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 warned that though the general process is simple, there 

 are difficulties in particular cases. In the Pulmonata, for example, membranes on 

 both sides of the radula need careful removal. Murex, Purpum, 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 Pisaoa like Turritclla, Harpa, or Struthiolaria, or 



