326 GENERAL ZOOLOGY 



source of variation. He accepted variations as facts and 

 analyzed the manner in which they are continued or eliminated. 



A more modern point of view (Cuenot) maintains that varia- 

 tions arise independently of any utilitarian value, but after their 

 appearance they may or may not become useful. Organisms 

 are preadapted. In the struggle for existence the new variations 

 become useful if the bearer can find an "empty place" in nature 

 where its new variations are of real service in the struggle for 

 existence. The bearer of the new variations is fully adapted. 

 There is no slow process of "fitting" into the new environment. 

 In other words, the organism does not develop characters adapted 

 to its environment, but chooses or finds an environment that is 

 compatible with whatever equipment it has. The skin of the 

 frog is adapted to a moist environment; but the nature of the 

 skin also acts as an effective bar to living in a dry atmosphere. 

 The nature of the skin makes it necessary for the frog to live in a 

 moist environment. 



Some deny that structure has any adaptive meaning. For 

 example, most aquatic birds have webbed toes, but the moor hen 

 (Gallinula chloropus), a bird of distinctly aquatic habits, has toes 

 without webs. There are also some terrestrial birds with inter- 

 digital membranes. Many other cases might be cited in which 

 well-developed structures seem to be without adaptive value. 

 How can these apparent exceptions be reconciled to what appear 

 to be adaptive structures in other forms? In biology as in other 

 sciences no law has an absolute and uniform value. "The laws 

 are the common resultant of a large set of particular facts not 

 identical, but statistically compensatory" (Caullery). The 

 webbed toes of aquatic birds occur in sufficient frequency to be of 

 statistical value and are certainly correlated with aquatic life, 

 regardless of exceptions. "It is not likely that pure chance had 

 resulted in such a statistical uniformity of conformation." 



What, then, is the relation of adaptation to. environment? 

 Lamarck's idea of direct effect of the environment lacks support 

 and cannot be accepted in its original form. On the other hand, 

 the environment does play a part in the development of certain 

 characters in some animals. An often cited example is that of the 

 European cave salamander, Proteus anguinus. Under natural 

 conditions in the dark, the body is pale, but if kept in the light, 

 the pigment appears. The basis for pigment formation is present 



