EVOLUTION OP THE CHICK. 167 



it is indispensable for the chick to turn gradually 

 round, till it has completed an entire revolution ; 

 though this circumstance cannot, in consequence of 

 the opacity of the shell, be actually observed. The 

 demonstration of the inference, however, is completed 

 by the several places at which the point of the bill 

 appears, whilst the head is kept constantly under the 

 same wing ; a position so strictly preserved, that it is 

 persisted in even for some time after the separation 

 of the shell into two portions, leaves the chick a door 

 almost as large as the dimensions of his prison. The 

 revolution which the chick thus makes on his own 

 body is invariably from left to right, and it is pro- 

 bably performed by means of the feet ; for the claws, 

 on pressing the shell through the membrane that 

 separates them from it, must find in that shell the 

 resistance necessary to effect the required circular 

 motion. This notion is corroborated by the circum- 

 stance of the feet alone enabling the chick to effect 

 its exit ; for the wings and other members, with the 

 exception of the neck and bill, are incapable of any 

 action so long as the chick is in the shell. Reaumur, 

 being curious to ascertain the mode of the circular 

 movement of the chick, was not contented with mere 

 probability, but had recourse to experiment. 



" Is it," he asks, " contrary to probability that 

 the strokes of the bill upon the shell exert a reaction 

 on the body of the chick sufficient to alter its posi- 

 tion, and turn it by little and little round the circle ? 

 A plain experiment seemed to me well adapted to 

 determine this ; founded on the principle, that if the 

 notion was correct, the chick could not turn itself if 

 the bill were so placed as to have nothing solid to 

 press against, a condition easily produced, by taking 

 from the bill that solid support against which it was 

 supposed necessary for it to act, or protracting the 



