242 CLASSIFICATION OP THE ANIMAL KINGDOM. 



produce and prolong those notes of music which in the spring and early 

 summer months, and even in the warmer winter days, may be heard 

 enlivening our woods, lanes, and hedge-rows. The kidneys of birds are 

 always of a large size, and the generative system is quite as simple in its 

 structure as that of reptiles. 



The young, while confined in the egg, pass through many most wonderful 

 and interesting changes, or rather gradual developments, as regards heart, 

 lungs, and circulatory apparatus, before they are hatched and make their 

 first appearance in the world as highly organized members of the Vertebrate 

 division of the Animal Kingdom. 



The nervous system, in accordance with the never-failing rule, presents 

 a very perceptible improvement in comparison with that of reptiles, more 

 especially, says Professor Jones, "in the increased proportional development 

 of the cerebral hemispheres;" but it is still inferior to that of the highest 

 class next to be considered in several important points. The senses of 

 touch and taste are but imperfectly developed, while those of smell and 

 sight are, on the other hand, very highly brought out, to enable the birds 

 to scent the least waft of carrion that may taint the atmosphere, and to 

 discover the lurking prey while sailing at a great distance above, or gliding 

 quickly through the air. The eye in birds is admirably constructed, and 

 is provided with three moveable eyelids — an upper, and a lower, and the 

 nictitating membrane, which is in a measure transparent, and the lacrymal 

 and other glands. The sense of hearing in birds is like that of the more 

 perfect reptiles, there is still no external ear, though the owl tribe possess 

 a broad sinus flap, which somewhat resembles the more highly-organized 

 auditory apparatus of the next class. 



We now come to the last class of the animal world, at the head of 

 which stands man, as far pre-eminent over all the tribes and genera below, 

 as his nervous system exceeds theirs in perfection. One of the great 

 distinguishing characteristics of this favoured class, and one which is never 

 met with in the lower families, is the production of milk for rearing their 

 young. Their skeletons, which in man and all other mammals except 

 cetacea, are divisible into five parts, — the cervical, dorsal, lumbar, sacral, 

 and caudal, are of endless variety and shape, and always singularly and 

 perfectly adapted to the circumstances of the different species to which they 

 belong. 



The more we examine the principles of nature, the more must we be 

 convinced of the consummate wisdom of its divine author, and this is 

 nowhere more strikingly displayed than in the formation of the skeletons 

 of the different tribes of mammals; as, for instance, the disproportionate 

 size of the hind legs, and length of tail of the kangaroos, fitting them to 

 escape when pursued, by strong and vigorous leaps; the conversion of the 



