EYES 47 



certain students claim that there is some evidence of 

 that part of the ear (cochlea) which appreciates pitch 

 being found in frogs, it is, if there at all, very rudi- 

 mentary. This may be the reason why they croak in 

 such rasping quavers. Any one near a croaking frog 

 can feel his ear-drums fairly flutter in the coarse 

 vibrations. 



As in fishes, it is not improbable that the sense- 

 glands of the lateral line also may aid the tailed 

 forms to appreciate jarring sounds. 



Eyes 



In the frog-forms the eyes are very good, being 

 usually fairly large and projecting. The eye is not 

 so large anywhere as we should expect in creatures 

 so nocturnal as many amphibians are, but this is 

 probably accounted for in the great range of the size 

 of the pupil. Those which, when examined in day- 

 light, appear as slits are doubtless large and circular 

 at night, as are those of the cat. Whether the pupil 

 be a horizontal or a vertical slit, whether triangular 

 or circular in daylight, these are very characteristic 

 marks of various species. It seems that the vertical 

 pupil implies more nocturnal habits than any other 

 shape. 



Frogs have some muscles which aid them in pro- 

 jecting the eye upward for observation. Those which 

 haunt the water have projecting eyes which, with the 

 nostrils, can be thrust above the water while the body 

 is beneath. There is no partition of bone between 

 the eye-sockets and the mouth, so that if the mouth 



