ANOTHER WORLD DOWN HERE. t 9 



such vibrations as continuous sounds when they amount to 

 about thirty per second. The insect's continuous sound prob- 

 ably 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 

 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 companions the common 

 cockroach or black-beetle will reveal two round white points, 

 somewhat higher than the base of the long outer antenna, 

 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 hav- 

 ing this external transparent tough membrane which corre- 

 sponds 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 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 that out- 

 spread of the optic nerve forming the retina. There does not 

 appear to be in this or other insects a tightly stretched mem- 

 brane which, like the membrane of our ear-drum, is fitted to 

 take up bodily air-waves and vibrate responsively to them. 

 But it is evidently adapted to receive and concentrate some 

 kind of vibration, or motion, or tremor. 



What kind of motion can this be ? What kind of per- 

 ception does this curious organ supply ? To answer these 

 questions we must travel beyond the strict limits of scientific 

 induction and enter the fairyland of scientific imagination. 

 We may wander here in safety, provided we always remem- 

 ber where we are, and keep a true course guided by the com- 

 pass-needle of demonstrable facts. 



I have said that the cornea-like membrane of the insect's 

 ear-bag does not appear capable of responding to bodily air- 

 waves. This adjective is important, because there are vibratory 

 movements of matter that are not bodily but molecular. An 

 analogy may help to render this distinction intelligible. I may 

 take a long string of beads and shake it into wavelike move- 

 ments, the waves being formed by the movements of the whole 

 string. We may now conceive another kind of movement or 

 vibration by supposing one bead to receive a blow pushing it 



