47 



In regard to the mode of action of the apparatus, 

 Huxley came to the conclusion that the " cartilages " 

 which support the radula were perfectly passive and 

 that the radula was pulled backwards and forwards, 

 as a strap over a pulley or a polished surface, so that it 

 scraped the object like a rasp or file. This was the result 

 of observations on some living gastropoda. Geddes held 

 the opposite view, a view formerly hinted at by Cuvier, 

 to the effect that the action of the radula was due to the 

 muscles pulling the whole tongue up and down. 



My observations lead me to support Oswald, who 

 asserted that both these movements played a part; but 

 those described by Huxley seem, at the same time, to be 

 the most important. 



The mere fact of the attachment of the muscles to 

 the odontophoral cartilage shows that this is not 

 altogether passive. Again, the effect of the dorsal 

 retractors pulling on the radula would be to cause the 

 cartilage to move dorsally, but this would only happen 

 to any extent if the radula were fixed securely against 

 the cartilage. Most of the muscles, however, are 

 inserted in such a way that much power would be lost 

 if they were only moving the cartilages ; in fact, 

 it would be difficult to account for their positions. 

 Furthermore, there can be little play for the cartilage 

 in the securely bound up odontophoral mass. One would 

 conclude, therefore, from the anatomy alone that the 

 rasping movements of the radula over the cartilage were 

 the most important, whilst at the same time this 

 structure was not altogether passive. Any doubt, 

 however, was dispelled by one of the whelks actually 

 attacking the finger of the author and rasping away for 

 a few seconds on the skin. The median teeth of the 

 radula are so placed that at the point of reflection of the 



