2 S 2 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



sume that visual space-perception should begin at a 

 definite period of embryonic or post-embryonic de- 

 velopment. And yet the matter is in no way different 

 for psychic phenomena, if we realise that what we call 

 psychic is only a metaphysical term for functions of 

 associative memory. Just as our dioptrical apparatus 

 can only begin to function after the eye has reached 

 a certain stage of development, the mechanism of as- 

 sociative memory can only begin to function after the 

 brain has reached a certain stage of development. 

 And just as only certain animals are provided with 

 apparatus for visual space-perception, only certain ani- 

 mals are provided with the mechanism necessary for 

 associative memory. 1 I think it is time for us to re- 

 alise that some of the phenomena of embryonic de- 

 velopment are not continuous processes but decidedly 

 discontinuous. This is, of course, less obvious if we 

 limit our study of the organism to methods of stain- 

 ing and sectioning, but it becomes very striking if 

 we add some physiological methods. A pure -- n 

 NaCl solution is extremely poisonous to the eggs of 

 Fundulus during the first twelve hours. After that 

 it is decidedly less harmful. There is then a discon- 

 tinuity in the physical or chemical conditions of that 

 embryo at about twelve hours after fertilisation. An- 

 other discontinuity is connected with the beginning 

 of circulation. Before circulation begins a -| n KC1 

 solution is no more harmful to the embryo of Fundulus 



1 These considerations dispose also of the conception of consciousness in 

 plants or of the barbarous notion of consciousness in molecules and atoms. 



