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allantois then gradually shrivels up and its circulation is cut off. On 

 the twenty-first day the chick bursts the shell and emerges. It is 

 quite a capable youngster at hatching, for it can walk, and see, and 

 within a few minutes begins to peck at the ground. This is quite in 

 contrast with the situation in many other birds, whose young are 

 hatched in a naked, blind and entirely helpless condition. As a rule, 

 birds that nest on the ground have precocious young at hatching and 

 are called Prcecoces or Nidifugoe; while birds that nest in trees or in 

 other safer retreats have helpless young and are called Altrices or 

 NidicoloB. Intermediate conditions are of course found in many 

 species, especially in those of sea-birds, such as petrels and gulls, 

 whose young are downy at hatching, but stay in the nest for some 

 time. 



Nesting Habits of Birds. — Any adequate account of the nesting 

 habits of birds would require a volume in itself, for there are countless 

 different kinds of nests and of materials used. The more primitive 

 nests appear to be crude nests built on the ground, consisting of mere 

 hollows scooped out of the sand or earth after the manner of some of 

 the reptiles. Some birds have no nests at all but merely lay the eggs 

 on rocks; this is probably not a primitive, but a degenerate habit. 

 The members of the higher orders of birds, as a rule, make nests out 

 of grasses or other materials that are suitable for weaving a fabric or 

 basket-Uke container for eggs. These nests are placed in trees, on 

 cliff-sides, in hollow trees, in burrows under the ground or in caves. 

 Clay or mud nests are common, especially among swallows. Birds 

 that occupy territory inhabited by man are quick to adopt the va- 

 rious materials that man furnishes, such as string, rags, paper and 

 other common waste. The use made of various man-made bird 

 houses illustrates the fact that the bird is decidedly adaptable and 

 not stereotyped in its form of intelligence. 



