44 THE POPULAR SCIENCE MONTHLY. 



our human point of view is that of supposing human intelligence to 

 be the only kind of intelligence in existence. The fact is, that what 

 we call the lower animals have special intelligence of their own as far 

 transcending our intelligence as our peculiar reasoning intelligence ex- 

 ceeds theirs. We are as incapable of following the track of a friend 

 by the smell of his footsteps as a dog is of writing a metaphysical 

 treatise. 



So with insects. They are probably acquainted with a Avhole world 

 of physical facts of which we are utterly ignorant. Our auditory ap- 

 paratus supplies us with a knowledge of sounds. What are these 

 sounds? They are vibrations of matter which are capable of produc- 

 ing corresponding or sympathetic vibrations of the drums of our ears 

 or the bones of our skull. When we carefully examine the subject, 

 and count the number of vibrations that produce our world of sounds 

 of varying pitch, we find that the human ear can only respond to a 

 limited range of such vibrations. If they exceed three thousand per 

 second, the sound becomes too shrill for average people to hear it, 

 though some exceptional ears can take up pulsations, or waves, that 

 succeed each other more rapidly than this. 



Reasoning from the analogy of stretched strings and membranes, 

 and of air vibrating in tubes, etc., we are justified in concluding that 

 the smaller the drum or tube the higher will be the note it produces 

 when agitated, and the smaller and the more rapid the aerial wave to 

 which it will respond. The drums of insect-ears, and the tubes, etc., 

 connected with them, are so minute that their world of sounds prob- 

 ably begins where ours ceases ; that what appears to us as a continuous 

 sound is to them a series of separated blows, just as vibrations of ten 

 or twelve per second appear separated to us. We begin to hear such 

 vibrations as continuous sounds when they amount to about thirty per 

 second. The insect's continuous sound probably begins beyond three 

 thousand. The blue-bottle may thus enjoy a whole world of exquisite 

 music of which we know nothing. 



There is another very suggestive peculiarity in the auditory appa- 

 ratus of insects. Its structure and position are something between 

 those of an ear and of an eye. Careful examination of the head of 

 one of our domestic companions the common cockroach or black- 

 beetle will reveal two round white points, somewhat higher than the 

 base of the long outer antennae, and a little nearer to the middle line 

 of the head. These white projecting spots are formed by the outer 

 transparent membrane of a bag or ball filled with fluid, which ball or 

 bag rests inside another cavity in the head. It resembles our own eye 

 in having this external transparent tough membrane which corresponds 

 to the cornea ; which, like the cornea, is backed by the fluid in the 

 ear-ball corresponding to our eyeball, and the back of this ear-ball 

 appears to receive the outspreadings of a nerve, just as the back of 

 our eye is lined with the outspread of the optic nerve forming the 



