THE MOLLUSCAN RADULA. 127 



marginals pass by many gradations of form into the lateral 

 teeth. These outermost pieces, on the other hand, present a 

 sudden change in the series of marginals, being longer than 

 their neighbours, and agreeing in their staining properties 

 with the marginals of Patella. In fact, the reactions to stains 

 almost tempt us to suggest that the teeth generally regarded 

 as marginals are multiplied laterals, and that the marginals 

 are i-epresented by these deeply staining teeth at the outer- 

 most edge of each row. 



Haliotis and Emarginula give somewhat similar results. 



T^NIOGLOSSA. 



Littorina littorea furnished the chief and most con- 

 venient material for the investigation of this group. The 

 radulae were dissected out from a thousand individuals of 

 the species, and dried at 100° C. ; they weighed 0'430 grm., 

 and afforded, on incineration, O'OloS grm, of ash, or 3"7 per 

 ceut. This was found to contain iron, calcium, and mag- 

 nesium. A second experiment was made on the ribbons of 

 several thousand individuals, from which 0"0508 ash was 

 obtained; this yielded 0*0083 of phosphoric acid, or rather, 

 of P3O5, corresponding to 16"3 percent, or to 35*6 of calcium 

 phosphate. A contrast between the staining reactions of the 

 marginals and the central and lateral teeth exists here as in 

 the case of Patella, though it is less marked (fig. 9), and the 

 teeth run through the same stages as regards staining 

 capacity during their growth as in that genus, but in the 

 long radula sheath it is noticeable that the teeth retain for a 

 long time their afhnity for the common stains, and only quite 

 near to the mouth-cavity become green under the action of 

 Bethe's stain. Their great hardness is discovered when an 

 attempt is made to cut sections of the buccal mass. Previous 

 treatment with nitric acid is necessary for success in this 

 process. 



