284 



EVOLUTION AND ANIMAL LIFE 



been done to test the truth of the mechanical assumptions 

 is a fascinating chapter in the history of modern biological 

 work. 



In sum we may say that there has been in recent years a 

 real advance on a basis of experimental work, in the analysis 

 of many vital phenomena long considered mysterious, or at 

 least too complex for human understanding, into simpler 

 components. And that these components are in many cases 



no other than reac- 

 tions and motions 

 familiar to us in in- 

 organic nature. On 

 the other hand it 

 must be said that 

 this advance, in the 

 face of the immense 

 problem presented 

 by vital reactions — 

 that is, the behavior 

 of organisms — is very 

 small. With all our 

 heart we should wel- 

 come all attempts to 

 do awav with ideas 

 of mysticism in con- 

 nection with biologi- 

 cal phenomena ; the 

 mechanists should 

 have our strong sym- 

 pathy and our willing 

 support, but to join 

 the more radical of 

 them in their claim 

 that the life mystery 

 is already solved in terms of physics and chemistry, that there 

 is no longer any vital problem, would be to surrender our 

 judgment to our inchnation. 



Any discussion, however brief, of experimental work in 

 biology should include a reference, at least, to the striking and 

 suggestive results that have been obtained by the application 

 of the experimental method to the investigation of the problems 



Fig. 167. — Regeneration of the earthworm : A, Nor- 

 mal worm ; B-F, anterior ends of worms which, after 

 the removal of one two, three, four, and five seg- 

 ments, have regenerated the same number ; G, an- 

 terior third cut off, only five head segments regener- 

 ated ; H, worm cut in two in middle, a head-end of 

 five segments regenerated ; I, worm cut in two be- 

 hind the middle, a heteromorphic tail regenerated at 

 anterior end. (After Morgan.) 



