o52 THE REPRODUCTIVE FUNCTIONS. 



this hard shell, which had hitherto afforded it pro- 

 tection, is now opposed to its emancipation; and 

 the chick, in order to obtain its freedom, must, by 

 main force, break through the walls of its prison ; 

 its beak is, however, as yet too tender to apply 

 the force requisite for that purpose. Here, again, 

 we find Nature expressly interposing her assist- 

 ance ; for she has caused a pointed horny pro- 

 jection to grow at the end of the beak, for the 

 special object of giving the chick the power of 

 battering its shell, and making a practicable breach, 

 through which it shall be able to creep out, and 

 begin its new career of life. That this horn is 

 provided only for this temporary use appears from 

 the circumstance of its falling off spontaneously in 

 the course of three or four days after it has been 

 so employed.* 



But though the bird has now gained its liberty, 

 it is still unable to provide for its own maintenance, 

 and requires to be fed by its parent till it can use 

 its wings, and has learned the art of obtaining 

 food. The pigeon is furnished by nature with a 

 secretion from the crop, with which it feeds its 

 young. In the Mammalia the same object is pro- 

 vided for still more expressly, by means of glands, 

 whose office it is to prepare milk; a fluid which, 

 from its chemical qualities, is admirably adapted 

 to the powers of the digestive organs, when they 

 first exercise their functions. The Cetacea have 

 also mammary glands ; but as the structure of the 

 mouth and throat of the young in that class does 

 not appear adapted to the act of sucking, there has 



* Further details respecting this curious process are given by Mr. 

 Yarrell, in the Zoological Journal, ii. 436. 



