130 



SOME MOLLUSCAN RADUL^. 



(Presidential Address delivered at tlie Annual Meeting, Oct. nth, 1913). 



Bv The Rev. Professor II. M. GWATKIN, D.D., M.A. 



My first duty here is to express my sense of the honour you have 

 done me in raising to this place of dignity an amateur like myself, 

 whose life's work has been done on other fields than those of science. 

 Yet, such scientific work as I have been able to do has been some- 

 thing more than a priceless relief and rest from the arduous work 

 officially entrusted to me. It 1ms been a strong and subtle influence 

 pervading and transforming those other duties in ways which few can 

 imagine and none can understand but those who follow both lines of 

 study with full-hearted love. If I believe, as indeed I do believe, that 

 science cannot satisfy the deepest needs and loftiest aspirations of 

 human nature, I believe also that all history and all theology which 

 is unscientific in its method is essentially unsound. Truth in all its 

 range is one and indivisible, and there is but one sound method in 

 all search for truth— that all facts must be taken into full account, 

 and all authority must go for nothing. There is genuine science in 

 Butler's Analogy or Westcott's Gospel of St. John ; genuine religion 

 in the patient labours of a Herschel or a Darwin. The two lines of 

 study are more akin than the narrower votaries of either are willing 

 to allow. 



Coming down, however, from these high themes to the little corner 

 of science where it has been my privilege to learn something, it is but 

 a single character found only in some of the moUusca — the radula. 

 Before we go further, it may be well to give a general account of it, 

 with chief, though not exclusive reference to the Fuhnonata, with 

 some of which we shall have to deal presently. 



The radula, then, is an organ found only in the moUusca; and even 

 among these it is wanting in the bivalves and in a few degraded 

 genera, like Magilus or Fyrajiiidella, though never in the Pulmonata. 

 If the name radula conveys no more information than that it is a 

 scraping organ, it has the negative merit of warning the unwary that 

 it is not equivalent to the tongue or palate of higher animals, but 

 something peculiar. It consists of what are called teeth, set on a 

 transparent membrane, wanting in Conns and Bela, but never in the 

 Pulmonata. Its average length is almost twice its breadth, though it 

 is notably shorter in some of the arboreal genera, like Aniphidromns, 

 Oxystyla, Achatinella, and some species of Drymceus^ and notably 

 longer in the carnivorous Agnatha, Ancylus and some of its allies, 



