IX 



Moreover, abundant references to literature are made throughout, 

 so that the student who wishes to refer to or read the various authors 

 in their respective languages, will find his labour appreciably 

 facilitated. 



The examples, chosen from biological sciences and more especially 

 from morphological descriptions, for illustrating the applicability 

 of the symmetry-principle in this province, have no claim to 

 absolute correctness. It is in general impossible for a chemist or 

 physicist to judge the exactness of such descriptions in morpho- 

 logy by means of drawings only, unless he has by chance gone into 

 these subjects in detail. The instances mentioned must be considered 

 as somewhat preliminary, intended only to prove the possibility 

 of a form-description based upon the principle of symmetry. How- 

 ever, it will not give much trouble to biologists to find the right 

 symmetry of each object, if only the general principles are once 

 clearly understood by them. The author will be grateful for sug- 

 gestions offered by his colleagues in a kindly spirit. 



When the present work was almost finished, a copy of a 

 little book in the Russian language from the hand of Professor 

 G. W. Wulff: cHMMETpm H EH npojia;iEHiE Bb iiPHPoat. (Symmetry and its 

 Manifestations in Nature), came into the author's possession. It 

 contains a short review of four lectures delivered by the writer 

 in 1907, at the request of the Society for Popular University Instruc- 

 tion in Moscow. As the range and design of these lectures are obviously 

 quite different from those of the present volume, there was no reason 

 for the author to consider his book as superfluous and to give up 

 its publication. 



If the contents should instigate our students of natural philosophy 

 and our future investigators to some new experiments or to any 

 applications in the different fields of research, the writer would 

 think himself amply rewarded for the work done in composing 

 this book. 



