20 INTRODUCTION 
experience of practical breeders; only the elucida- 
tion of one simple rule of inheritance has brought into 
order a host of phenomena, which were previously quite 
incapable of a coherent explanation. 
The experimental results with which it is the pro- 
vince of this book to deal are, then, firstly those of 
biometry, or the statistical study of variations, and 
particularly of continuous variations ; secondly, the 
results of direct observations bearing upon the origin 
of species by the discontinuous method ; and thirdly, 
the results of experimental observations on heredity 
by the methods of scientific breeding. By these 
methods results of the utmost moment to mankind 
have been, and are being, arrived at, quite apart from 
their interest as bearing upon the problems of evolu- 
tion. From a biologist’s point of view, however, the 
latter is, of course, paramount. And so it has been 
thought fitting to begin with a brief discussion of the 
problems of evolution, and of the various solutions of 
them which have been from time to time suggested. 
In a later chapter some of the more prominent recent 
results of the kindred science of cytology—the micro- 
scopic study of the minute constituent parts of organ- 
isms—will be briefly described, on account of the very 
close connection which recent progress in this subject 
bears to the experimental study of the inheritance of 
the grosser characters. 
Finally, we have essayed a brief account of the 
science to which the name of ‘ Eugenics’ has recently 
been applied by Sir Francis Galton. In the chapter 
dealing with Eugenics an attempt is made to show 
i 
