OBJECTIONS TO LAMARCK'S THEORY in 



petal ' and * Centrifugal ' might be employed to express 

 this acquired difference.^ Acquired characters are centri- 

 petal, because they are impressed upon the body or one 

 of its parts from without ; inherent characters are centri- 

 fugal, because, arising from within due to the essential 

 nature of the organism itself, in the course of development 

 they come to appear, as it were, on the surface as visible 

 features. 



When we now consider the transmission of acquired 

 characters, upon which the Lamarckian Theory certainly 

 depends, we are led first of all to inquire whether it is 

 possible to frame a theory of heredity within which such 

 transmission can be included. If, for instance, there is 

 a change in the brain of an animal, owing to the exercise 

 of some part of it, how can such a change in the brain- 

 cell be transferred to the germ-cells of the animal, so as 

 to be transmitted to its offspring ? It may be objected, if 

 you can prove that such transmission does take place, it is 

 no matter how it takes place. Quite true, if the evidence 

 is sufficient and indisputable. But we must remember 

 that the amount of evidence required, in order that there 

 may be sufficient, depends upon the probability or impro- 

 bability of the thing to be proved. This view is extremely 

 well put by Professor Huxley in his memoir of Hume, 

 where he says that if any one came to him and stated 

 that he had seen a piebald horse in Piccadilly he would 

 be prepared to believe it ; that he might require con- 

 firmatory evidence if the statement were that a zebra had 

 been seen ; but that if even the friend in whom he trusted 

 told him he had seen a centaur trotting down that eminent 

 thoroughfare, he should emphatically disbelieve it, and 

 that nothing short of a monograph on the anatomy of the 

 centaur by a comparative anatomist of the stamp of 

 Johannes Muller would convince him that the observation 

 was correct. We are compelled to admit that the amount 

 of evidence we require does to a great extent depend 

 upon the inherent probability or improbability of the 

 conclusion to be sustained. If it appears to us to be 

 almost impossible to conceive of a mechanism whereby 



^ See page 123. 



