ANOTHER WORLD DOWN HERE. 43 



ject, 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 be- 

 comes too shrill for average people to hear it, though some 

 exceptional ears can take up pulsations or waves that suc- 

 ceed each other more rapidly than this. 



Seasoning from the analogy of stretched strings and 

 membranes, and of air vibrating in tubes, etc., we are justi- 

 fied in concluding that the smaller the drum or the 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 probably begins where ours ceases ; that the sound 

 which appears to us as continuous is to them a series of sep- 

 arated blows, just as vibrations of ten to twelve per second 

 appear to us. We begin to hear such vibrations as contin- 

 uous 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 aud- 

 tory apparatus 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 compan- 

 ions the common cockroach or black-beetle will reveal 

 two round white points, somewhat higher than the base of 

 the long outer antennse, 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 exter- 

 nal transparent tough membrane, which corresponds to the 

 cornea or transparent membrane forming the glass of our 

 eye-window ; which, like the cornea, is backed by the fluid 

 in an ear-ball corresponding to our eye-ball, and the back 

 of this ear-ball appears to receive the outspread ings of a 

 nerve, just as the back of our eye is lined with that out- 

 spread of the optic nerve forming the retina. There does 



