THE NEW EVOLUTION 



He found that the sensitivity to saccharose of the 

 organs of taste situated in the tarsi (feet) of that 

 common butterfly known as the red admiral (Cynthia 

 atalanta) may be on occasion two hundred and fifty- 

 six times as great as that of the human tongue. 



Dependence on special senses, which is well illus- 

 trated by birds, bats and many insects, is an important 

 factor in biology. For such close dependence on a 

 narrow range of stimuli carries with it both great 

 advantages and great disadvantages. 



The chief advantage is that extraordinary develop- 

 ment of a special sense overcomes competition in all 

 lines of activity which are dependent on or are chiefly 

 aided by that special sense — provided, of course, that 

 bodily structure and control are of such a nature as 

 to permit that special sense to function to the best 

 advantage. 



The chief disadvantage is that dependence on a 

 special sense limits bodily control largely to that 

 sense and hence renders the animal dependent in 

 greater or lesser measure upon the maintenance un- 

 changed of those external conditions by which that 

 sense is activated. Let those conditions change, and 

 become such that the special sense no longer functions 

 to the best advantage, and the animal is placed at once 

 under a serious handicap duetotheunder-development 

 of all the other senses. 



Dependence on a special sense or on a relatively 

 narrow range of special conditions always results in a 

 more or less marked subordination of all the features 

 of the animal type involved to the requirements of 



[86] 



