CHAPTER X 
THE ORIGIN OF THE DIFFERENT KINDS OF 
ADAPTATIONS 
In the present chapter we may first consider, from the 
point of view of discontinuous variations as contrasted with 
the theory of the selection of individual variations, the 
structural adaptations of animals and plants, ze. those 
cases in which the organism has a definite form that adapts 
it to live in a particular environment. In the second place, 
we may consider those adaptations that are the result of the 
adjustment of each individual to its surroundings. In sub- 
sequent chapters the adaptations connected with the 
responses of the nervous system and with the process of 
sexual reproduction will be considered. 
It should be stated here, at the outset, that the term 
mutation will be used in the following chapters in a very 
general way, and it is not intended that the word shall 
convey only the idea which De Vries attaches to it; it is 
used rather as synonymous with discontinuous and also defi- 
nite variation of all kinds. The term will be used to include 
“the single variations” of Darwin, “sports,” and even ortho- 
genic variation, if this has been definite or discontinuous. 
Form AND SYMMETRY 
Almost without exception, animals and plants have defi- 
nite and characteristic forms. In other words, they are 
not amorphous masses of substance. The members of each 
species conform, more or less, to a sort of ideal type. Our 
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