228 BOAED OF AGRICULTURE. 



I propose to show you, as far as it can be shown without a 

 specimen in hand, how this is brought about. The process 

 has been observed in a large number of cases. Its limits and 

 various modifications in different animals are extensively 

 known, and were it not for our ignorance of the process within 

 these very creatures, which have for us such a special interest, 

 we might congratulate ourselves upon our results. 



As an illustration recalling something with which we are 

 familiar is more impressive, perhaps, than an allusion to 

 things less known or less frequently seen, I will take my 

 description mainly from the egg of the hen. Suppose you 

 remove from the egg, first, the solid limestone shell, then the 

 membrane lining the shell, and lastly, the second or inner 

 membrane immediately surrounding the yolk. A separation 

 between these two membranes at the blunt end of the egg 

 forms the air-chamber. The air-chamber is full of a white 

 substance capable of coagulating under heat, and possessing 

 all the properties of albumen ; in fact, it is living albumen. 

 This brings you to the innermost part of the egg, where you 

 find a sphere of yolk about the size of a walnut. This sphere 

 has grown gradually to its present condition by the multipli- 

 cation of those infinitely small organic elements which physi- 

 ologists call cells, and which are, as it were, the bricks out of 

 which the living structure is built. These cells multiply by 

 producing new generations of cells within themselves ; which 

 are then set free by the bursting of the outer envelope, and in 

 this way the yolk is constantly increased in bulk. This proc- 

 ess goes on all the time while the yolk is forming, enlarging, 

 and transforming itself into a new being. 



The yolk is suspended within the second or inner membrane 

 by two strings of white, a little firmer in consistency than the 

 rest of the albumen, and it swings upon these two strings in 

 such a manner as to retain always the same position. On 

 one side of the yolk, when the egg has been laid, you may 

 see, on opening the shell, a little white speck ; that is the 

 beginning of the germ ; naturalists call it the blastoderm. I 

 will rapidly explain how that is formed. The whole yolk, 

 as I have said, consists of myriads of minute cells, — each of 

 which is in itself a complete organism. Every such cell in 

 its most perfect condition is a spherical body, containing a 



