CHAPTER XVI 

 CHEMICAL CORRELATION 



The Necessity for Gradual Adjustments. — In the 

 chapter just finished the means whereby animals adapt 

 themselves promptly and efficiently to the varied require- 

 ments of an ever-changing environment have been out- 

 lined. The general topic of the adjustment of organisms 

 has, however, not been completely considered until ac- 

 count has been taken of the many gradual adjustments 

 which organisms have to make. Numerous examples of 

 these gradual adjustments will be considered in the para- 

 graphs below. Here, by way of illustration, need be 

 mentioned only two : in plants, the ripening of the fruit 

 is an adjustment which serves the biological requirements 

 of the plant, and it is an adjustment which goes on gradu- 

 ally. It is not only gradual but it is a genuine adjust- 

 ment, that is to say, the chemical changes which consti- 

 tute ripening occur at a definite time in relation to the 

 development of the seed, as well as to the general growth 

 activities of the plant. A gradual adjustment in animals 

 is the adjustment of symmetrical growth. If one stops 

 to think about it he may well inquire how it happens 

 that the two ears, which are separated from each other 

 by the width of the head, manage to grow at a uniform 

 rate and to stop their growth at the same time, so that 

 in the majority of people the two ears are of the same size. 

 Here is just one of the numerous adjustments that occur 

 in animal growth and without which misshapen and dis- 

 torted bodies would inevitably result. It is clear that a 

 mechanism like the nervous system is not well adapted 

 for making adjustments of this character. To maintain 



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