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P R E S I D li K T I A L A D D K E S S . 



(Delivered 13th February, 1914.) 



SOME POINTS AND PROBLEMS OF GEOGRAPHICAL DISTRIBUTION. 



]}y the Rev. A. H. Cookk, M.A., D.Sc, F.Z.S. 



I KisE to address you to-uight, in accordance with the custom — 

 desirable perhaps from your point of view, quite the reverse from 

 mine — whicli imposes upon j'our President for the time being the 

 task of delivering an annual disquisition on some branch of 

 malacological science. You will not expect from nie, and you 

 will certainly not receive, an address that will bear any comparison 

 with those of my predecessors, in respect either of encyclopoedic 

 knowledge or powers of exposition. You must have been well 

 aware, when you placed me in the position which I have the honour 

 to occupy, that my hours of scientific leisure were but few, and that 

 I was of necessitv, though not of choice, in respect of the objects of 

 our common worship, " parens deorum cultor et infrequeus." 



I propose for your consideration a few points and problems of 

 Geographical Distribution, relating wliolly to the Marine MoUusca. 

 My endeavour will be, not so mucli to solve these problems as to 

 raise them, perhaps to propose difficulties rather than to suggest 

 exphmations. One of the soundest ways of learning is, and has 

 been from the time of Socrates till now, by grasping the fact of our 

 own ignorance. And one has little fear that nature will have, even 

 for our children's children, no secrets still to be revealed. 



Geographical distribution, if one may so put it. forms a kind of 

 background or setting to the whole study of zoology. The subject of 

 our investigation, whatever it may be, lives its life within a certain 

 definite area or areas of the earth's surface, to the exclusion of the 

 rest — it is ' here' and not ' there '. To state the fact is to invite the 

 demand : Why are certain forms of life found in some localities and 

 other forms in other localities ? Modern science answer's the question 

 by pointing out a certain correspondence between the organism and 

 its environment, between the circumstances of life and the power to 

 live. AYhen we find an organism living under surroundings, 

 whether of food, light, temperature, soil, etc., which enable it 

 to attain, so far as we can judge, the maximum of its efficiency, and 

 produce descendants equally efficient, we speak of it as enjoying tlie 

 optimum of environment, and, so long as this optimum of environ- 

 ment is maintained, so long, other things being equal, will the 

 organism continue to live ami flourisli. On the other hand, if certain 

 of its surroundings become continuously and considerably modified, 

 if, in other words, the environment begins to decline from the 

 optimum, the organism may and probably will be modified also in 

 a manner adverse to its perfect development. And if this process of 

 change in the environment becomes emphasized and prolonged, it may 



