254 EXPERIMENTAL EVOLUTION LECT. 



with it, and cannot be separated, concerning which 

 information will be most valuable, from the practical 

 as well as from the scientific point of view. Some of 

 these questions may be briefly indicated. 



First the question of variability in species, or other 

 groups, and how they are established. External and 

 internal or physiological variability must both be in- 

 vestigated anew, with the most delicate tests and 

 methods, and particular attention must be directed to 

 their causes. Of course, this study implicates that of 

 species. What is a species ; what are specific charac- 

 ters ? If we consider many of the recognised species, 

 we see that these characters are often of the most 

 insignificant sort, and that many of the so-called 

 specific characters are even of less value than those 

 which are used to distinguish varieties. It may be 

 predicted that terrific discussions will arise concerning 

 this vexatam questionem, which seems to become more 

 intricate every day, and that much sorrow will befall 

 that numerous and well-disposed class of systematists, 

 whose self-assumed task in life seems to be to in- 

 crease the list of specific forms. Perhaps we shall 

 thus understand what really makes a species ; for 

 while we talk much about them, we really do not 

 understand what they are, and no thorough definition 

 has yet been given. 



The problem of heredity will also be investigated, 



