MAMMALIA. 469 



whole band follows him, observing the strictest dis- 

 cipline. As the duties of the leader are very arduous, 

 and as he cannot support them during the wdiole 

 voyage, he may be perceived, when overcome with 

 fatigue, to yield his post toMiis 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 Avay. 



CHAPTER XXYII. 



Mammalia.* 



The essential character wliereby this class of animals 

 is distinguished from all others, is that the creatures 

 composing it bring forth living young, w^hich 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 mani- 

 fested to an extent unparalleled in the preceding 

 orders of Vertebrata ; but it is to the Mammalia alone, 

 tlie most sagacious and intelligent of all the in- 

 habitants of this world, that the Creator has pei'- 

 mitted 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 production of milk for the nourish- 

 ment of their young, the Mammalia are distin- 

 guished by the following peculiarities : — They all 

 breathe air by means of lungs, suspended freely in 

 a cavity, wl\ich is separated from the abdomen by 



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



