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THE PRESIDENT'S ADDRESS. 



SOME PROBLEMS OF EVOLUTION IN THE 

 SIMPLEST FORMS OF LIFE. 



By Prof. E. A. Minchin, M.A., V.-P.Z.S., F.L.S. 



{Delivered February 2St7i, 1911.) 



Gentlemen, 



When we survey with comprehensive outlook the world 

 of animated beings around us, our senses, or rather the limita- 

 tions of our senses, suggest to us at once a subdivision of living 

 things into two categories, which are natural and obvious from 

 a human standpoint, though not necessarily scientific on that 

 account. In the first place, there is the every-day visible world 

 of animals and plants, familiar to us since we first opened our 

 eyes on this planet, in all its variety of character and luxuriance 

 of form. In the second place, there is the invisible world of 

 minute life which the microscope reveals to us, no less varied 

 or exuberant than that of which we are made aware by our 

 unassisted vision. 



Taking first that visible world of living creatures with which 

 every human being is acquainted, no deep reflection or analysis 

 is required to grasp the fact that it does not constitute a chaos 

 of isolated and unconnected forms, but is capable of being 

 classified into greater or lesser categories. Popular speech shows 

 us that the most uninstructed person is aware of this, though it 

 may be unconsciously. The first and most obvious division of 

 visible living things is into animals and plants. So far scientific 

 and popular opinion are in accord, and the same is true, more 

 or less, with regard to the smallest groups of forms that receive 

 a common name, namely, kinds or species. Such words as cat, 

 horse, dog, elm, oak, correspond fairly closely with species or 

 groups of species recognised by the scientific man. 



But between the categories of greatest and least extent, there 

 are a number of intervening subdivisions, with regard to which 

 the scientific and the non-scientific public are hopelessly at 

 variance. The same is inevitably true in any branch of know- 



