THE PSYCHICAL FACULTIES OF ANTS AND SOME OTHER 



INSECTS." 



By A. FoREL. 



A fine example of the fact that complicated psychical combinations 

 require a large nerve center having- under its control the sensory and 

 motor centers is afforded b}^ the brain of the ant. An ant colony is 

 usually made up of three kinds of" individuals — females (the largest), 

 smaller workers, and males, who are rather larger than the workers. 

 The workers have, more than an}' of the others, complicated instincts, 

 and with them intellectual faculties (memory, plasticity, etc.) are 

 readil}' demonstrable. The females have much less. The males are 

 incredibly stupid; they do not distinguish friends from foes, and 

 are unable to find their way to the nest. They have, however, well- 

 developed eyes and antenna?; that is to say, the only two sense organs 

 that are connected with the brain or supra-esophageal ganglion, and 

 these enable them to successfully pursue the female in flight. No 

 muscle is innervated from the supra-esophegeal ganglion. This fact 

 makes very much easier the comparison of the organ of thought— 

 i. e., the brain {Q)7'j)ora jyedunculata) — in the three sexes. It is ver}" 

 large in the workers, much smaller in the females, almost atrophied in 

 the males, though the olfactory and optic lobes are in the latter quite 

 large. The cerebrum of the ant workers possesses also a cortex 

 extraordinarily rich in cells. Injury to the cerebrum in ants is fol- 

 lowed by results similar to those which occur in the pigeon. 



Insects appear to possess sight, smell, taste, and touch. Hearing is 

 doubtful. It is possibh^ replaced by a tactile sense modified for deli- 

 cate appreciations of concussion. A sixth sense has never been 

 demonstrated. A modified photodermatic sense for perception of 

 light must be considered as a variety of the tactile sense, and occurs 

 among many insects. This is in no way an optical sense. In water 

 insects, smell and taste become somewhat blended (Nagel), for chemical 

 substances dissolved in water are detected bv either sense. 



« Transl-ited and condensed from the Proceedings of the Fifth International 

 Zoological Congress, held at Berlin, August 12-16, 1901, pp. 141-169. 



587 



