CHAI-. iv. DEVELOPMENT OF CHICK. 619 



germ of the male bird must fertilise that of the female, ere can arise 

 the new existence which every life represents. A fertilised egg is 

 subject to many contingencies, and may never hatch, but there is, at 

 least, the possibility, which does not exist in the unfertilised egg. 

 Here it may be well to mention that an unfertilised egg will not become 

 rotten, and in hatching it is desirable to remember that should an egg 

 prove rotten there has been life, but that death has occurred at an 

 earl}' stage of development. An infertile egg becomes stale, but that 

 is all. 



The process of development which the chicken undergoes within the 

 shell must be very briefly summarised, but the illustrations (figs. 172 

 to 176) will indicate some of the stages. 



First day Germ begins to expand ; 



Second day Germ expanded still more, and veins formed ; 



Third day Brain and eye take definite form, and blood veins 

 become thicker and more definite (fig. 172) ; 



Fourth day There appears a respiratory membrane called the 



Fig. 176. Development of Chicken Exit from the Shell. 



allantois, which, lining the shell, temporarily provides for the supply of 

 oxygen to the blood ; 



Seventh day By this time the internal organs, including the heart, 

 liver, kidneys, &c., have assumed their definite shape (fig. 173) ; 



Tenth day Bones begin to assume a decided consistency, and scales, 

 legs, and feathers, may be seen ; 



Twelfth day The living organism begins to give out heat, showing 

 that the heart is performing its work, and the blood becoming richer 

 (fig. 174). From this time onward the chick begins to grow in size ; 

 at the 



Fifteenth day filling about two-thirds of the shell (fig. 175), and so it 

 continues to progress until about the 



Twenty-first day, when (fig. 176) it bursts its envelope and emerges 

 therefrom, the yolk bag having been absorbed into the body a few hours 

 previously. 



The selection of birds for breeding is a very important matter, more 

 important than is generally supposed, for parents impress upon their 



