434 Mr. Yarrell on the horny appendage to the 



gravings) as the most recent and complete statements of this 

 interesting and beautiful part of physiology. 



It is not upon any of these particulars, already so well detailed, 

 that I am about to presume to oifer any observations, but to point 

 out a small horny appendage near the end of the upper mandible 

 of the chicken, and describe its particular use while the young 

 bird remains confined within the shell of the egg; which al- 

 though not overlooked, has probably been considered of little 

 consequence compared Avith more important objects of investiga- 

 tion, but is yet adapted to perform a very necessary part ; and re- 

 mains as far as I am acquainted at least, unnoticed in print. 



The yolk of the egg is suspended within the white by its cha- 

 lazes or poles, which not being inserted in the line of its axis, the 

 larger portion of the yolk gravitates, and the cicatricula or mole- 

 cule destined to become the chick being placed on the surface of 

 the smaller portion of the yolk, will always be found uppermost 

 whatever may be the position of the egg. That this peculiar 

 arrangement leads to important results will be hereafter shewn, 

 and I hope to be excused inserting here one note from the paper 

 by Dr. Prout, in the Philosophical Tranactions before quoted, 

 from its immediate reference to this point. 



*' An interesting circumstance may be here mentioned, which 

 I have never seen noticed by any writer on the present subject. 

 A.t the end of the process of incubation, and for some time be- 

 fore, the animal is so situated in the egg, as, by its superior 

 weight on one side to assume such a position that the beak shall 

 be uppermost, and consequently fully exposed to the air when it 

 first makes its way through the shell." 



During the exhibition of Mr. Ba!h)w's ingenious apparatus for 

 hatching chickens by steam, I had daily opportunities of observ- 

 ing the changes that take place in the egg ;* but I shall pass over 

 these, and advance to the seventeenth day, during which, pro- 



* The most curious part of this apparatus appeared to be the construction 

 and adaptation of thermometrical levers, which, influenced by the internal 

 degree of temperature, and acting upon certain valves, admitted or excluded 

 atmospheric influence, by which the heat within the machine was kept con- 

 stantly ranging within four or five degrees of the standard required. 



