96 REPRODUCTION 



changes for the chick at the moment of hatching. Up to 

 this time the oxygen, which is necessary for all life, passes 

 through the shell and finds its way into the blood directly 

 by means of some special embryonic membranes. When 

 the chick breaks the shell these membranes dry up and all 

 the oxygen goes into the lungs in the ordinary way. 

 Before hatching all the food has been taken by the blood 

 from the substances in the egg. Almost immediately after 

 hatching the chick begins to practice its instincts for 

 pecking at food, and soon gets to using its digestive tract. 

 Other vital activities follow and the young chick soon 

 performs all the important functions in just the same way 

 the adult does. 



6. The Sexes in Birds. The males and females are 

 always distinct in birds. That is to say, one individual 

 produces sperms and another eggs. Furthermore, the two 

 parents, when adult, are usually quite unlike in appearance, 

 instincts, and behavior. The chicken is a good illustration 

 here, though not better than many other birds. The 

 rooster is larger, more brilliantly colored, more 

 aggressive, more noisy, and has certain structures which 

 the hen either does not have, or not in such degree, as 

 spurs for fighting, comb, wattles, etc. In many birds the 

 male has better developed powers of song. It is thought 

 that many of these qualities in which male and female 

 birds differ are adaptations that enable each the better to 

 meet the work which it must do. For example, the spurs 

 of the cock, his greater size, and his aggressiveness seem 

 to fit in with the fact that in some measure he takes the 

 lead and protects the flock that surrounds him. 



Birds have power to reproduce only by the union of 

 sperms and eggs. 



