ADAPTATION 245 



Mimicry. This characteristic is common in insects. Some cater- 

 pillars can scarcely be distinguished from a dead twig; in form, 

 color, and behaviour when they are disturbed the imitation is 

 very nearly perfect (Fig. 148). Other insects resemble leaves, 

 still others the bark of trees, and some, flowers or other insects. 

 The effect is either concealment, for protection or aggression, or 

 safety through the mimic's power to profit by some repulsive 

 quality of the imitated. 



Concealment through mimicry is often imperfect. The bilateral 

 symmetry of many moths resting on tree trunks discloses their 

 presence rather easily to the practiced eye, though it is impossible 

 to know how many are passed by unnoticed. One species, Stenoma 

 schlaegeri and probably other related species of the same genus, 

 conceals its symmetry by lapping one front wing over the other; 

 this moth resembles a small l)ird-dropping so closely that either 

 maj' easily be mistaken for the other. 



The explanations of adaptation are many. Whether we shall 

 ever know how all of them have come about is very doubtful, for 

 the details of the problem are infinite. They are universal, how- 

 ever, and afford us unlimited material for the study of evolution- 

 ary processes. From such studies theories have been formulated 

 to explain the modification of organisms and in these theories we 

 find the probable foundations of this varied and intricate associa- 

 tion of organisms and environments. It is certain that some 

 process or processes of change have given rise to the modern 

 condition since evolution points to a common origin for all living 

 things. 



Summary. Adaptations are the characters of organisms which 

 fit them for hfe in a given environment. In the individual we 

 see both the process of adaptation and the adaptations resulting 

 from it, while in species we see only the latter. It is the function 

 of evolutionary theory to account for the wonderful adaptations 

 which are characteristic of species. When we consider the environ- 

 ment with which they are associated we find that it involves 

 external factors, both physical and organic, and in addition the 

 internal environment which the individual body furnishes for any 

 of its parts. Adaptations which are due to response to conditions 

 of the internal environment have been called non-adaptive char- 

 acters but they must be due to cause and effect no less than 

 characters directly related to the external environment. The 



