EVOLUTION OF THE CHICK. 1C9 



food, and for this purpose the unconsumed portion of 

 the yolk enters through the navel. The chick, in- 

 deed, which comes out of the shell before taking up 

 all the yolk is certain to droop and die a few days 

 after it is hatched. The help which I have occa- 

 sionally tried to give to several of them towards their 

 deliverance, has afforded me an opportunity of ob- 

 serving those which had begun to break their shells 

 before this was accomplished ; and I have opened 

 many eggs much fractured, in each of which the 

 chick had as yet much of the yolk not absorbed. 

 Besides, some chicks have greater obstacles to over- 

 come than others, since all shells are not of an equal 

 thickness nor of an equal consistence; and I think 

 it probable that the same inequality takes place in 

 the lining membrane. The shells of the eggs of 

 birds of various species are of a thickness pro- 

 portional to the strength of the chick that is obliged 

 to break through them. The canary-bird would 

 never be able to break the shell it is enclosed in 

 if that were as thick as the egg of a barn-door 

 fowl ; and the latter would crush all the eggs she 

 might attempt to sit upon, if their shells were as 

 thin as those of a canary-bird. The chick of 

 a barn-door fowl, again, would in vain try to 

 break its shell if it were as thick and hard as that of 

 an ostrich ; and even though an ostrich ready to be 

 hatched is perhaps thrice as large as the common 

 chick, it is not easy to conceive how the strokes of 

 its bill can be strong enough to break a shell thicker 

 than a china cup, and whose smoothness and gloss 

 indicate that it is nearly as hard, sufficiently so in- 

 deed to form, as I have often seen, a solid drinking- 

 cup. It is the practice in some countries to dip the 

 eggs into warm water at the time they are expected 

 to chip, on the supposition that the shell is thereby 

 rendered more fragile and the labour of the chick 



Q 



