EVE OF ESCAPE. 303 



strength and vigour of the chick, and partly also 

 upon the variable thickness and density of the 

 shell. It has been stated that toward the com- 

 pletion of incubation the shell becomes more 

 brittle than at its commencement ; the statement, 

 however, requires additional evidence for its con- 

 firmation. Very often the fracture does not 

 extend all the way round the shell It is fre- 

 quently only prolonged to about three-quarters 

 of the circumference. The lining membrane is of 

 course separated as well as the shell ; the latter, 

 however, commonly flies off the membrane in small 

 pieces, the membrane being broken through by a 

 subsequent impulse of the bill. 



The prisoner is on the eve of effecting his escape ! 

 " He thinks he has," says Reaumur, " and he has in 

 reality 5 strength enough to separate the fore part, 

 or largest end of the shell, from the other at the 

 instant when they no longer adhere to each other, 

 but by a small portion of the circumference. If 

 his bill is no longer wanted to complete that 

 separation, the chicken brings it about more 

 efficaciously and more speedily by applying the 

 whole mass of his body. He makes an effort by 

 stretching out his feet to push his body a small 



