ORIGIN OF ADAPTATIONS AND OF SPECIES 247 



have so many characters in common that the separation into 

 species becomes an arbitrary matter, depending upon the good 

 judgment of the systematist, who if wise, is neither a 

 " lumper " nor a " splitter." At present, the minutely dis- 

 criminating powers of an unfortunately large number of ento- 

 mological systematists are displayed in an extraordinary mul- 

 tiplication of generic and specific names, often to the sacrifice 

 of convenience and stability of nomenclature. This has been 

 carried to such an extent, however, that a reaction has already 

 set in, and there is now some promise of a rational termi- 

 nology. 



Considering characters as of specific importance only, it 

 makes no immediate difference whether they are adaptive or 

 not. If adaptive, whatever their origin, they may have been 

 developed by natural selection; if not, they are incidental, and 

 may be due to such influences as those next to be referred to. 



Climate and Food. Naturalists have recorded many in- 

 stances in which plants or animals when transferred to a new 

 climate have produced offspring markedly different from the 

 parent form. The term climate, however, has no precise 

 meaning for the naturalist, referring as it does collectively to 

 several distinct influences, chief among which are tempera- 

 ture, moisture, light and (indirectly) food conditions. Ex- 

 perimental evidence has already been adduced to show that 

 color changes in insects may be brought about as direct effects 

 of warmth, cold, light or food. Some of these color varia- 

 tions are possibly inheritable, and many of them, artificially 

 produced, would be regarded as distinctive of new species, if 

 found in a state of nature. In fact, the distinction between 

 varieties and species is often entirely arbitrary; varieties are 

 incipient species and it is often impossible to draw any sharp 

 line between the two. 



Mutation Theory. De Vries' mutation theory, expounded 

 in 1901 as the result of nearly twenty years of experimenta- 

 tion, is at present an absorbing subject of study and discussion 

 in the biological world, and will continue to be for many years, 

 until the full bearing of the theory is ascertained. 



