EXTENSION OF EVOLUTIONARY THEORIES 355 



suitably to their suddenly altered conditions of life. We 

 saw that, generally speaking, animals have the power of 

 suitable reaction or adaptation only in their customary 

 environment. A mole-cricket tries to bury itself in a 

 glass plate instead of running away ; a bee stings a 

 human being, though the sting will be fatal to itself, 

 and so on. If the purposive reaction in the vital force 

 of animals were independent of the external world they 

 would be armed against all contingencies ; and that is 

 not the case. Far more probable is our hypothesis that 

 the animal's power of adaptation has arisen by gradual 

 development under the controlling influence of external 

 agencies. 



Matter and force determine the series of cause and 

 effect, as we know from experience. To this no 

 exception has been found. On the other hand 

 there are many exceptions to the purposive power of 

 organisms ; and that shows it is not determined by any 

 internal law. 



We have a proof of non-purposive development in the 

 rudimentary organisms. Humanity would be far better 

 off if the human frame contained no coecum. How 

 frequently, moreover, the "purposive power" goes 

 astray during embryonic development, and brings into 

 the world hydrocephalous children and other deformities. 

 Then there is the power of regeneration ; it would be 

 of great service to all animals, but is found well 

 developed in very few. Do not some animals have a 

 larger measure of it than others? Why, then, are 

 they particularly favoured ? In a word, the vital force 

 raises so many new difficulties that are not raised by 



