EVOLUTION OF THE CHICK. 163 



stance, that pieces of the shell are often broken and 

 driven off to some distance, while the membrane 

 within remains unruptured, which it is supposed could 

 not happen if the fracture were made on the inside by 

 the chick. But it might on the same principle be 

 argued, that a wine-glass covered with parchment 

 could not be broken by the stroke of a hammer with- 

 out rupturing the parchment ; for the membrane of 

 the egg is elastic and yielding, while the shell is not. 

 That the chicken, however, and not the mother, per- 

 forms this office, has been proved by direct observa- 

 tions, which may be readily verified. It is worthy of 

 remark, that the fact was correctly stated so long ago 

 as the thirteenth century, by Albertus Magnus, the 

 great naturalist of the dark ages *. 



It might be supposed that this task was much 

 above the strength of the yet feeble chick, did we not 

 reflect that the anxiety it must feel to escape must 

 add greatly to its energy, which is farther aided both 

 by its peculiar structure, and by the position it as- 

 sumes. The bill is still soft, indeed, and to a care- 

 less observer would seem ill fitted for breaking the 

 shell ; but, superadded to the bill, " upon the curved 

 part of the upper mandible," to use the words of 

 Mr. Yarrel, " just above the point there will be seen 

 a small horny scale, nearly circular, having at its 

 centre a hard and sharp projecting point, and by the 

 particular position of the head, this sharp point is 

 brought into constant contact with the inner surface 

 of the shell.'* It is worthy of remark, that the only 

 use of this horny point seems to be to break through 

 the shell, for when the chick escapes, and the beak 

 hardens by exposure to the air, it soon falls off, and 

 on the second or third day, only a light-coloured 

 mark is observable on the spot which it had occupied. 

 It may, indeed, be easily separated by the thumb-nail 

 * Apud Aldrovand, Ornith.iii. 184, ed. Francofurti. 



