3lK THE REASON WHY : 



See how she gasps, and struggles hard for life." LLOYD. 



it is supplied with breath, and which adhere together when 

 deprived of their natural element. 



1136. Why are certain species of fish constituted to live for 

 a long period out of water '< 



Because they inhabit ponds and streams in warm countries, 

 where, in many situations, there is an ample supply both of food 

 and water for fish during the rainy season; but a complete 

 deficiency of both when this is succeeded by a periodical drought. 

 Such receptacles can only be tenanted by fish which are fur- 

 nished with the peculiar apparatus for keeping the gill moist ; since, 

 when one pond or stream is dried up, they can migrate in search of 

 another. In the course of these journeys, they climb up steep 

 banks, and even trees ; and, by a remarkable instinct, they 

 seem always to travel to the nearest water. 



1137. Why is that part of the fish's eyes known as the 

 crystalline lens, much rounder than in the eyes of the terrestrial 

 animals ? 



Because the rays of light, in passing from water into the eye, 

 require to be refracted by a more convex surface than when it 

 passes out of air into the eye. 



1138. As an illustration of the instances adduced here, of the adaptation of the flsh'f 

 eye to the medium in which it lives, we may observe that the power in the human 

 eye, for example, of drawing the pencil of rays to a focus, and producing an accurate 

 image upon the retina in the bottom of the eye, depends principally upon two circum- 

 stancesthe form of the cornea and 

 the convexity of the iens. That the 

 cornea may produce this effect, it is 

 not only necessary that it should he 

 convex, as in fig. 1 , but that the rays 

 should enter it from a rarei medium. 

 As this cannot be effected inthe water, 

 the lens or crystalline humour, 

 which is much denser than water, ii 

 brought into operation. In the eye of an animal living in the atmosphere, the leus 



