120 VARIATION IN LEPTINOTARSA. 



environmental factors, in plausible juxtaposition, and base far-reaching con- 

 clusions thereon ; but in any such process there are far too many assumptions 

 that this possible factor and that observed result are cause and effect. The 

 fact is lost sight of that the causes are numerous, and their action only 

 remotely comprehended. Too often we neglect to consider tendencies inher- 

 ent in the species, or to learn its physiology, its peculiarities of development, 

 its habits and instincts, and much other information which is apparently of 

 slight consequence, but which is of great importance in the economy of the 

 species. It is necessary to know our material intimately and to experiment 

 widely before we attempt to correlate observed variations with environmental 

 factors or to determine the causes and methods of evolution. 



