THE SEX SAT IONS OF ANTS. 509 



experimentation and observation. I have emphasized them because 

 they seem to have been ignored by some investigators. 



Although touch is one of the most important senses of ants, it has 

 not been thoroughly studied in these insects. Its great delicacy is 

 attested by the number, distribution and structure of the tactile hairs 

 or sensilhe. As these are extremely fine and abundant on the antennal 

 funiculi, we are justified in concluding that the latter are -the principal 

 organs of touch and as the moving ant continually palpates and explores 

 the surfaces over which she travels, it is not improbable that she gleans 

 perceptions of the forms of objects. But it is impossible to dissociate 

 this mechanical sense from the chemical or olfactory sense, since the 

 organs of both are not only situated in the same antennal joints, but 

 are intermingled with one another. It is probable that ants also per- 

 ceive tactile stimuli to the general chitinous integument where it is not 

 furnished with hairs. That these insects have a very delicate tempera- 

 ture sense, although the location and nature of its organs are quite 

 unknown, is shown by many of their habits, notably by the way they 

 regulate their hours of activity and the way they place their brood in 

 the best situations for utilizing the warmth of the earth and stones. 

 That ants are capable of feeling pain hardly admits of doubt, for, as 

 Forel says : " They often exhibit unequivocal signs of discomfort, espe- 

 cially when their antennas are pinched, or when their nerve terminations 

 come in contact with certain corrosive or strongly irritating substances/' 

 But the quiet manner in which an ant, that has just had an antenna, 

 a leg or even her abdomen cut off, will gorge herself with honey, shows 

 that her sensation of pain must differ profoundly, both in q'uality and 

 intensity, from that which we should suffer from similar operations. 



Much more attention has been devoted to the study of the sense 

 of smell than to that of touch. Forel (1874, 1878^), the pioneer in 

 this field of investigation and the one who has established all the impor- 

 tant facts, found that many ants, when deprived of their antennae, not 

 only do not attack alien ants, but even lick them, that they cannot care 

 for the young or excavate the nest, and are able to eat only when they 

 stumble on their food by accident. Such ants also make unusual move- 

 ments with their legs and palpi in attempting to substitute these 

 organs for their missing antennae. Forel believes that the pros- 

 trate, club-shaped sensillae (see Chapter IV, p. 62) are the principal 

 olfactory organs, because they are the ones best developed in insects 

 with the keenest sense of smell (e. g., in Ichneumon flies). Ants are 

 able to perceive odors diffused in the air as well as those dissolved in 

 liquids ; for even the blind species often stop and wave their funiculi 

 about in a peculiar manner when within a short distance of an odorous 



