MAMMALS. 359 



to yield his post to his next neighbour, and fall again into the ranks at the 

 extremity of one or other of the files. Some species fly alone, and singly 

 undertake their long and trackless voyage, solitary, but not unguided by the 

 Hand that points their way. 



FIG. 397. BEAK OF DUCK 



CHAPTER XXVII. 



FOURTH CLASS OF VERTEBRATE ANIMALS. 

 MAMMALS.* 



THE essential character whereby this class of animals is dis- 

 tinguished from all others is that the creatures composing 

 it bring forth living young, which they suckle, and thus nourish 

 for a time with their milk. In birds, the duties and the pleasures 

 inseparable from the necessity of incubating their eggs, and of 

 providing nutriment for their callow brood, are indeed manifested 

 to an extent unparalleled in the preceding Orders of Vertebrate 

 animals ; but it is to the Mammals alone, the most sagacious and 

 intelligent of all the inhabitants of this world, that the Creator 

 has permitted the full endearment of paternal and maternal love, 

 has thrown the offspring, absolutely helpless, to be dependent on 

 a mother's care and solicitude, and thus confers upon the parent 

 emotions that a mother only knows, the dearest, purest bestowed 

 upon animal creation. 



Besides the leading feature of their economy, namely, the pro- 

 duction of milk for the nourishment of their young, the Mammals 



* From "mamma," the breast : because they suckle their young. 



