74 THE REASON WHY 



But, as an old booke saith, who will assay 

 About the enfs nccke to bans; on a bett, 

 Had first need to cut the cat's clawes away. 



nnchecked, speedily create famine. The design, therefore, in 

 the universal distribution of carnivorous creatures is to restrain 

 the too rapid increase of vegetable feeders, by which scarcity of 

 <rar own food would soon be created. 



220. The myriads of insects which find their subsistence on our forest-trees, if 

 allowed to feel-ease without restraint, would soon destroy the Kfe that supports them, 

 and must all then perish together ; but another tribe (that of the insectivorous birds 

 as the woodpecker) is adapted to derive its subsistence from them, and thus to keep 

 within salutary bounds the numbers of these voracious little beings. Sometimes,, 

 however, they increase to an enormous extent. Whole forests have been destroyed 

 fry the ravages of a single species of beetle, which is less than a quarter of an inch 

 in length. 



221. WTiy do the eyes of certain animals "glare" in tfa 

 twilight or dark? 



It was once supposed that the eyes of animals in which this 

 phenomena appears possessed the power of emitting light, and 

 acted as lanterns in the direction of the animal to seize its prey. 

 But this appears to be not the case. The light i reflected from 

 the choroid tissue, which has a sort of metallic lustre, and reflects, 

 after the manner of a concave mirror, a portion of the light which 

 enters the widely-distended pupil. It is not improbable that this? 

 reflected light is thrown upon the object which the animal desire? 

 to investigate or to seize. Although sntall in amount, it may 

 sufficiently illuminate an object to impress the highly sensitive 

 retina of the eyes of such of the feline species in which this 

 peculiarity is most exhibited, 



222. JThy do not their eyes glisten in the daylight? 



Because the aperture of the pupil is then contracted. The 

 light being thus excluded, the quantity which finds admission 

 to the eye, and falls upon the coat from which thw reflection 

 proceeds, is very small. But when the animal stands in a dark 

 shade, the pupil dilates, the reflecting coat is, as it weir, exposed, 

 and the eyes glisten just as much during the day as u> the 

 uight. 



