THE METHOD OF CREATION OF ORGANIC FORMS. 209 



that the presence of greater or less number of external facilities 

 for action characterize different situations on the earth's surface, 

 as well as that greater and less metaphysical capacity for perceiv- 

 ing and taking advantage of them must exist in different indi- 

 viduals of every species of animal, however low, which possesses 

 consciousness and will. These qualities must, of course, influence 

 effort and use to the advantage of the animal, or the reverse. 



Effort and use have very various immediate stimuli to their 

 exertion. 



Use of a part by an animal is either compulsory or optional. 

 In either case, the use may be followed by an increase of nutrition 

 under the influence of reflex action or of direct volition. 



A compulsory use would naturally occur in new situations 

 which take place apart from the control of the animal, where no 

 alternatives are presented. Such a case would arise in a submerg- 

 ence of land where land-animals might be imprisoned on an island 

 or in swamps surrounded by water, and compelled to assume a 

 more or less aquatic life. Another case, which has also probably 

 often occurred, would be when the enemies of a species should so 

 increase as to compel a large number of the latter to combat who 

 had previously escaped it. 



In these cases, the structure produced would be necessarily 

 adaptive. But the effect Avould sometimes be to destroy or injure 

 the animals (retard them) thus brought into new situations and 

 compelled to an additional struggle for existence, as has, no 

 doubt, been the case in geologic history. 



Direct compulsion would also exist where alternatives should 

 be presented by nature, but of which the animal would not be 

 sufficiently intelligent to take advantage. 



Most situations in the struggle for existence afford alterna- 

 tives, and the most intelligent individuals of a species will take 

 advantage of those most beneficial. Nevertheless, it is scarcely 

 conceivable that any change or increase of effort, or use, could 

 take place apart from compulsion derived from the relation of 

 external circumstances, as a more or less remote cause. 



Preservation, with modifications, would most probably ensue 

 when change of stimulus should occur gradually, though change 

 of structure might occur abruptly, under the law of expression 

 points. * 



* See " Origin of Genera," p. 38. 



