THE MOLLUSCAN RADULA. 117 



that the teetli do not dissolve in either acetic or nitric acid^ 

 while hydrofluoric acid corrodes them. No particulars of 

 their experiments are given. The same authors investigated 

 the teeth of Buccinum and came to the same conclusion. 



In 1852 Leuckart (9), beiug interested in the distribution 

 of chitin in the animal kingdom^ examined, among many 

 other objects, the radulas of Gastropoda and Cephalopoda, 

 and pronounced them to be chitin. He emphasised the fact 

 that his identification of chitin rested entirely on two 

 characters — one its resistance to caustic alkali, the other 

 its solubility in boiling nitric acid. He adds : " It is possible 

 that in this sense chitin is a collective conception, and that 

 many special modifications Avill be discovered later. Perhaps 

 we may conclude this from the varying behaviour of chitin 

 when treated with alkali," and he expresses a wish that 

 chemists would investigate the matter. About the same 

 time Bei-gh (4), without knowing of Leuckart's paper, con- 

 futed Hancock and Embleton's view, and demonstrated the 

 absence of silica in three species of Prosobranchiate 

 Gastropods. Bergh's is the first exact investigation ; we are 

 indebted to Troschel for a German translation of an extract 

 of his paper, which is written in Danish. Bergh showed that 

 in Buccinum antiquorum (Triton nodif erum), and in 

 Strombus gibberula most concentrated acids bring about 

 corrosion of the radula in the cold, and eventually complete 

 solution on boiling, while dilute hydrofluoric acid does not 

 alter the teeth in form, but renders them more transparent. 

 Incinerated ribbons of Marsenia perspicua gave no silica. 

 The radula of Buccinum antiquorum gave the reactions 

 of iron and calcium phosphate. 



Troschel was dissatisfied with what he considered the con- 

 tradiction in the results of Leuckart and Bergh,^ and there- 

 fore undertook with Bergemann experiments which combined 

 and reconciled the results of both these investigators. Helix, 



^ This remark seems hardly fair to Leuckart, wlio nowhere states that 

 chitin is the sole constituent of tlie radula and is not interested in the ash ; of 

 Bergh's paper I have only read the extract given by Troschel. 



