76 THE PASSENGER PIGEON IN PENNSYLVANIA 



seen on each side of the thread, the commencement of 

 the vertebrae. The parts seem to be a crystallization 

 from^ the substances of the egg. By the end of the 

 first day the germ curves, looking like a tiny maggot 

 as it lies on the edge of the yolk. The little heart is 

 perceptible, the second day ; the arteries and veins sup- 

 pHed with blood, are perceived the third day. So the 

 various organs appear, one after another, as the body 

 is built up; the feathers being the last, on the twelfth 

 day, and the squab pierces the air-sack, with its beak, 

 at the blunter end of the tgg; and hammers on the 

 shell with its horn-tipped beak. 



The young bird has been nourished by the yolk, 

 which is connected with its abdomen, and which is 

 separated soon after the shell is broken, enabling the 

 squab to respire freely. The shell is pecked in a cir- 

 cle, cutting for itself a trap-door, which often remains 

 suspended by a hinge of uncut lining membrane, 

 through which the squab emerges on the fourteenth 

 or fifteen day after the incubation began, and the 

 horny excrescence at the tip of its bill soon drops off, 

 as the young bird no longer needs a chisel to cut 

 through so hard a substance as an egg shell; and na- 

 ture abhors a superfluity in all of her craftsmanship. 

 The young bird remains in the nest, nourished by the 

 parents, for about two weeks, growing a coat of feath- 

 ers upon its naked body, and quills for wings and tail, 

 the sails and rudder by which it then parachutes from 

 the high branch of the home nest-tree, in a slanting 

 route, as it flutters to the ground and begins its life 



