THE BEASON WHY. 237 



" He that hath ears to hear, let him hear." MATTHEW xi. 



that there are some rays which are luminous to them which are 

 not luminous to us. Hence they find light in what we call darkness. 



982. Why does the pupil of a cat's eye appear nearly closed 

 by day? 



Because the cat's eye is so sensitive to light that the iris closes 

 the pupil almost entirely to shut out the too powerful light. 



CHAPTER XLIX. 



983. Why do we hear ? 



Because the tympanum of the ear receives impressions from 

 sounds, and transmits those impressions to the brain in a similar 

 manner to that in which the retina of the eye transmits the 

 impressions made upon it by light. 



984. Why is one part of the ear spread out externally ? 

 The external ear is a natural ear-trumpet, and serves to collect 



the vibrations of sound, and to conduct them towards the internal 

 ear. 



985. Why is the ear allowed to project, whilst the eye is 

 carefully enclosed ? 



Because the external ear, being formed of tough cartilaginous 

 substance, and being very simple in its organisation, is but little 

 liable to injury. 



986. Why do hairs grow across the entrance of the ears ? 

 Because they prevent the intrusion of insects, and of particles of 



dust, by which otherwise the faculty of hearing would be impaired. 



The insect called the ear-wig is popularly supposed to be so named from its 

 tendency to get into the human ear, and cause pain and madness by 

 penetrating to the brain. An earwig, however, is no more likely to get into 

 the ear than any other insect whose habit it is to penetrate the corollas of 

 flowers; and should an insect enter the ear, i could get no further than the 

 membrane of the tympanum,which spreads all over the auditory passage, just as 

 the parchment of a drum spreads over the entire circumference of that 

 instrument. The fact is, that the wing of the insect, when spread, resembles 

 the external ear in phape. I" is similar 4 o the wing of the stag beetle (see 

 Illustration), and this fancied resemblance of the wing of the insect to the ear 

 of man may have given rise to the name of ear-wing, which became corrupted 

 K> ear-wig. 



