280 GENERAL ZOOLOGY 



The long period of care-free youth which robins enjoy 

 enables them to reach a state of comparative independence 

 under the protection of the parents. They do not en- 

 counter the force of the struggle for existence until they 

 have attained somewhat of strength, vigor, and experience. 

 The egg cell is stored with yolk, fertilized, and has passed 

 through early segmentation stages before it is laid. As it 

 passes down the oviduct more nourishment is added around 

 the egg proper in the form of albumen, or " white," and the 

 protective shell is then formed on the outside. While the 

 young robin develops within the egg, it is constantly 

 warmed and watched by the parents. After hatching, 

 it is long the object of solicitous attention. Small wonder, 

 then, that most robin eggs come to maturity. 



A perch lays two thousand eggs, gives no attention to 

 its young, and most of them are destroyed. A robin lays 

 four eggs and usually brings all of them to maturity. Why 

 is one method better than the other? The net result in 

 either case will perhaps be two or three new animals from 

 each pair annually. The robin, however, has one ad- 

 vantage the young pass through a long adolescent period 

 during which they are cared for, and even trained to some 

 extent by having opportunity to imitate their elders. 

 The bird has more chance to acquire experience before 

 being thrown on its own resources, and this gives opportu- 

 nity for a higher grade of psychic development. 



GENERAL REMARKS ON BIRDS 



Birds all agree in having feathers, beaks, arid .character- 

 istic feet, but all these structures show endless variations 

 which are usually correlated with differences in habits and 

 habitats. For example the feathers may be downy, or 

 stiff and hair-like; the feet may be webbedj feathered, or 

 naked; the beak may be hooked for tearing flesh, short and 

 heavy for cracking seeds, or long and slender for probing 

 in the mud. Each type of bird has the bodily parts highly 



