74 The Mechanistic Conception of Life 



simultaneously with the stimulus in question.^ If an animal 

 can be trained, if it can learn, it possesses associative memory. 

 By means of this criterion it can be showTi that Infusoria, 

 Coelenterates, and worms do not possess a trace of associative 

 memory. Among certain classes of insects (for instance, ants, 

 bees, and wasps), the existence of associative memory can be 

 proved. It is a comparatively easy task to find out which 

 representatives of the various classes of animals possess, and 

 which do not possess, associative memory. Our criterion 

 therefore might be of great assistance in the development of 

 comparative psychology. 



7. Our criterion puts an end to the metaphysical ideas that 

 all matter, and hence the whole animal world, possesses con- 

 sciousness. We are brought to the theory that only certain 

 species of animals possess associative memory and have con- 

 sciousness, and that it appears in them only after they have 

 reached a certain stage in their ontogenetic development. This 

 is apparent from the fact that associative memory depends 

 upon mechanical arrangements which are present only in certain 

 animals, and present in these only after a certain development 

 has been reached. The fact that certain vertebrates lose all 

 power of associative memory after the destruction of the cere- 

 bral hemispheres, and the fact that vertebrates in which the 

 associative memory either is not developed at all or only slightly 

 developed (e.g., the shark or frog) do not differ, or differ but 

 slightly, in their reactions after losing the cerebral hemispheres, 

 support this view. The fact that only certain animals possess 

 the necessary mechanical arrangements for associative memorj^, 

 and therefore for consciousness, is not stranger than the fact 

 that only certain animals possess the mechanical arrangements 

 for uniting the rays from a luminous point in one point on the 

 retina. The liquefaction of gases is an example of a sudden 



1 Loeb, J., "Beitrage zur Gehirnphysiologie der Wiirmer," Pflugers Archiv, 

 LVI, 247, 1894. 



