EXTENSION OF EVOLUTIONARY THEORIES 343 



no horny plates on the palate of the crocodile, the 

 dolphin, and other aquatic animals? The external 

 influence is the same in the case of all these animals. 

 Why is there a different reaction in the various animals ? 



And there is yet another question. What is the 

 extent of the influence of external stimuli ? If the 

 water causes horny plates on the palate of certain 

 animals, they must continue to grow indefinitely. If 

 apes have acquired certain protuberances by sitting, 

 these will go on growing until they become monstrous 

 swellings, if the effect of the stimulus is increased 

 with each generation. 



It has been said in reply that an organism at length 

 inures itself to these permanent stimuli, and ceases to 

 react on them. But this only raises another difficulty. 

 What is the basis of this power of adaptation ? Perhaps 

 it will be said that it depends on a certain adaptive 

 power of the body. But how did this come about? 

 And when the animal has become inured in this way 

 what is the service of it ? Moreover, it must last for a 

 longer or shorter period in different animals. 



In a word, we see that the action of external stimuli 

 in the transformation of organisms must be very slight. 

 The real force must lie within the animals themselves. 

 It is due to this that the body responds to external 

 stimuli in so far as it is to the interest of the animal. 

 The adaptiveness of living things, which must have a 

 scientific explanation, puts out of court all the Lamarckian 

 hypotheses, and therefore also orthogenesis. 



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It is the opinion of many authorities that natural 



