465 



THE PRESIDENT'S ADDRESS. 



THE BIOLOGICAL CONCEPTION OF INDIVIDUALITY. 



By Prof. Arthur Dendy, D.Sc, F.R.S. 



{Delivered February 23rd, 1915.) 



I need hardly remind you that the organic world, as we know it 

 to-day, is divided by systematic biologists, largely for their own 

 convenience and in accordance with their own particular ideas, 

 into some millions of different kinds or species of plants and 

 animals, and that each of these so-called species consists, usually 

 at any rate, of millions of units which we call individuals. 



In making this statement we most of us probably think 

 that, whatever may be our doubts as regards species, we know 

 very well what we mean by the term "individual"; we can 

 recognise and define an individual man or dog, or an in- 

 dividual oak tree or cabbage, at any rate to our own 

 satisfaction. If, however, we carry our investigations a little 

 below the surface of things w r e soon meet with cases that are 

 not a little puzzling, and my purpose this evening is to inquire, 

 albeit very briefly, whether it is really possible to frame a 

 definition of individuality from the biological standpoint that 

 will be of general applicability throughout the animal and 

 vegetable kingdoms ; whether we are really much better off in 

 this respect in dealing with individuals than we are in dealing 

 with species. 



There appear to me to be two main paths by which we can 

 approach our problem, the morphological and the physiological. 

 On the one hand we can inquire what constitutes a perfect 

 individual from the point of view of structure, and, on the other, 

 what constitutes such an individual from the point of view of 

 function. In the case of the higher animals we might approach 

 the question in a third way and inquire what constitutes an 

 individual from the psychological standpoint. We shall find, as 

 we pursue our investigations, that each path is beset with 

 difficulties, and that each leads to some very curious situations. 

 We shall also discover that the three paths are not entirely 



