Adaptation to Environment 343 



as adaptation when unknown turns out to be a result 

 of the action of a definite chemical substance circulating 

 in the body. 



It appears as a case of adaptation that the eggs of 

 the majority of animals cannot develop without a 

 spermatozoon, and yet we can imitate the activating 

 effect of a spermatozoon on the egg by definite chemical 

 compounds, which leads to the suggestion that the 

 activating effect of the spermatozoon on the egg might 

 be due to the fact that it carries such a compound. 



The wonderful adaptations exhibited in the mating 

 instincts seem to be due to definite substances secreted 

 by the sex glands, as was shown by Steinach (Chapter 

 VII). Here, again, the process as popularly conceived, 

 is the reverse of the truth; those survive that have the 

 equipment, — they did not acquire the equipment under 

 the influence of environment. 



It is absolutely imperative for green plants that their 

 stems and leaves be exposed to the light since only in 

 this way are they able to form carbohydrates; and it is 

 equally essential that the roots should grow into the soil 

 so that the plant may get the nitrates and phosphates 

 required to build up its proteins and nucleins. This 

 result is, in the language of adaptationists, brought 

 about by an adaptive response of the plant to the light. 

 In reaHty this adaptive response is due (Chapter X) 

 to the presence of a photosensitive substance present 

 in almost all green plants. 



