128 IGERNA B. J. SOLLAS. 



Rhachiglossa. 



In Buccinum undatum, as there are no marginal teeth, 

 the ribbon, doubly stained by the above method, does not 

 become marked out, as in previous cases, into a green median 

 region, bordered on eacli side by a red marginal baud ; none 

 of the teeth in the fully developed parts of the radula are 

 coloured by protoplasmic stains, but all take Bethe's stain. 

 It is noticeable that the teeth are very rapidly matured — a 

 necessary property in a tongue which must be quickly worn 

 out. In a specimen of Purpura lapillus I found every 

 one of the teeth in the mouth-cavity with cusps broken off. 

 It would seem as though the molluscan radula had become 

 adapted to hard work in two distinct ways : in the one case 

 it becomes very resistant through a long-continued process 

 of development — witness the long radula sac — in the other 

 a less strong radula is rapidly worn out and as speedily 

 renewed. 



PULMONATA. 



Helix aspersa. — A remarkable discrepancy was found to 

 occur in the behaviour of the radula of this species when 

 incinerated on different occasions. Several lots containing 

 from twenty to one hundred and fifty radulse were heated, in 

 some cases with an ordinary Bunsen burner in a platinum 

 crucible, in other cases with a Herapath. These experiments 

 were all made in winter-time, and all gave the following 

 result : the radula at first preserved its form in ash, but soon 

 fused with continued heating : it gave an exceedingly minute 

 fusible drop, which solidified to an enamel-like glass, yellow 

 when hot, white when cold. In winter, also, the ash was 

 always found to contain some silica : the ash from some 150 

 ribbons was boiled in fuming nitric acid, in this reagent it 

 proved only partially soluble ; the insoluble residue was 



