14 ANTS AND SOME OTHER INSECTS. 



ject, but it seemed necessary that we should come to some under- 

 standing concerning the validity of comparative psychology. My 

 further task now consists in demonstrating to you what manner of 

 psychical faculties may be detected in insects. Of course, I shall 

 select in the first place the ants as the insects with which I am 

 most familiar. Let us first examine the brain of these animals. 



In order to determine the psychical value of a central nervous 

 system it is necessary, first, to eliminate all the nerve-centers which 

 subserve the lower functions, above the immediate innervation of 

 the muscles and sense-organs as first centers. The volume of such 

 neuron-complexes does not depend on the intricacy of mental work 

 but on the number of muscle-fibres concerned in it, the sensory 

 surfaces, and the reflex apparatus, hence above all things on the 

 size of the animals. Complex instincts already require the inter- 

 vention of much more plastic work and for this purpose such nerve- 

 centers alone would be inadequate. 



A beautiful example of the fact that complex mental combina- 

 tions require a large nerve-center dominating the sensory and mus- 

 cular centers is furnished by the brain of the ant. The ant-colony 

 commonly consists of three kinds of individuals : the queen, or 

 female (largest), the workers which are smaller, and the males 

 which are usually larger than the workers. The workers excel in 

 complex instincts and in clearly demonstrable mental powers 

 (memory, plasticity, etc.). These are much less developed in the 

 queens. The males are incredibly stupid, unable to distinguish 

 friends from enemies and incapable of finding their way back to 

 their nest. Nevertheless the latter have very highly developed 

 eyes and antennae, i. e., the two sense-organs which alone are con- 

 nected with the brain, or supra-oesophageal ganglion and enable 

 them to possess themselves of the females during the nuptial flight. 

 No muscles are innervated by the supra-oesophageal ganglion. 

 These conditions greatly facilitate the comparison of the percep- 

 tive organs, i. e., of the brain (corpora pedunculata] in the three 

 sexes. This is very large in the worker, much smaller in the fe- 

 male, and almost vestigial in the male, whereas the optic and 

 olfactory lobes are very large in the latter. The cortical portion 



