lo Introductory Remarks 



mysterious influence of the whole on these parts con- 

 sists often merely of the fact that the circulating speci- 

 fic or non-specific substances — we cannot yet decide 

 which — will in the whole be attracted by certain spots 

 and that this will prevent them from acting on other 

 parts of the organism. If such parts are isolated the 

 substances can no longer flow away from these parts 

 and the parts will begin to grow. It thus becomes 

 utterly unnecessary to endow such organisms with a 

 "directing force" which has to elaborate the isolated 

 parts into a whole. 



5. The same difficulty which we have discussed in 

 regard to morphogenesis exists also in connection with 

 those instincts which preserve the life of the organism 

 and of the race. The reader need only be reminded of 

 all the complicated instincts of mating by which sperm 

 and eggs are brought together; or those by which the 

 young are prevented from starvation to realize the 

 apparently desperate problems in store for a mechanist, 

 to whom the assumption of design is meaningless. 

 And yet we are better off in regard to our knowledge 

 of the instincts than we are in regard to morphogenesis, 

 as in the former we can show that the apparent instincts 

 in some cases obey simple physicochemical laws with 

 almost mathematical accuracy. Since the validity of 

 the law of gravitation has been proved for the solar 

 system the idea of design in the motion of the planets 

 has lost its usefulness, and this fact must serve us as 



