

THE SENSES OF INSECTS McINDOO. 465 



particularly in the honeybee, is so highly developed that we do not 

 have any more conception of it than does the honeybee (if it could 

 think as we do) of our wonderfully developed sense of sight, which 

 is able to distinguish accurately the size, form, and color of objects. 



It has always been a matter of conjecture as to how the various 

 lower animals recognize each other, and by what means the sexes of 

 any species distinguish one another. At first thought it might be 

 claimed that sight is the chief means by which any animal having 

 eyes can recognize other animals, but after a second thought Ave recall 

 that the eyes in the lower animals are not as highly developed as 

 they are in the higher animals ; and we know that many of the lower 

 animals live in dark places and that some of them are partially or 

 totally blind. For example, the eyes of some beetles and spiders 

 inhabiting caves function little or not at all, and despite this fact, 

 these animals seem to distinguish one another as easily as do those 

 with normal eyes living in light places. Kelative to blind or partially 

 blind species, touch may be the chief means by which they recognize 

 one another, but during the courtship of cave spiders the writer ob- 

 served that the males recognize the females of the same species at 

 short distances and even before the males touch the webs of the fe- 

 males. Touch, therefore, can not be the chief means of recognition 

 for cave spiders and perhaps not for any other animal. Since we 

 know so little about the senses of hearing and taste in the lower ani- 

 mals, we may safely eliminate them as the chief factors in recognition. 



That the lower animals do recognize one another without using 

 the tactile organs, and as their sense of sight is not sufficiently de- 

 veloped to be the chief factor in recognition, we may assume that 

 the most important factor is some chemical sense, perhaps similar 

 to our olfactory sense. If the olfactory organs are the chief means 

 of recognition they must constantly receive stimuli in the form of 

 odors, and these odors must be emitted by the animals themselves. 

 If this is true, it would seem that the odor emitted by one animal 

 should be at least slightly different from that of any other animal, 

 and reasoning in this way Jaeger believes that most animals emit 

 odors peculiar not only to the individual, variety, race, and species, 

 but also to the genus, family, order, and class, and that these odors 

 are the chief means by which one animal recognizes other animals. 

 Without the aid of the eyes he claims that the degenerate human 

 olfactories are able to distinguish a horse from a cow, a goat from 

 a roe, a dog from a cat, a martin from a fox, a crow irom a pigeon, 

 a parrot from a hen, a lizard from a snake, and even a carrion crow 

 from a hooded crow. Blackman remarks that the anal mucous mem- 

 brane of our domestic animals, particularly the dog and cat, contains 

 glands whose secretion emits a comparatively mild odor, which prob- 

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