BIRDS ORGANIZATION DIAGRAM 4. 61 



enveloped in a sort of very slender skin, which forms two 

 ligaments, floating in the albumen towards the two ends of the 

 egg. We can also see, towards one end of the egg, a place 

 where the albumen does not touch the shell, and which is full of 

 air ; and this is called the air-sac. 



It is necessary for eggs to be kept at a raised temperature for 

 some time, in order to produce chickens. In this country, the 

 mother hatches the eggs by sitting on them, scarcely moving 

 from them at all, until the young ones are hatched. These 

 break the shell by pecking at it with their beaks ; they still 

 require to be brooded over by the mother for some time, and they 

 live under her until they are grown large. The heat and care of 

 the mother are not, however, indispensable to rear fowls, and they 

 can be hatched artificially by means of an arrangement called a 

 hatching oven, where the temperature is kept nearly equal, and 

 sufficiently high to develop the chick. With some precautions, 

 young chickens can thus be very easily reared. 



Birds generally build nests for breeding, which are sometimes 

 true masterpieces of architecture. Some are solidly built of 

 earth, others made of twigs ; there are 

 some which float on the water; and we 

 shall mention under each species any- 

 thing which is interesting about its nest. 

 But it ought to be thoroughly com- 

 prehended that no nests ought ever to be 

 destroyed, except those of birds of prey, 

 such as falcons or hawks. All other 

 nests ought to be respected. All young 

 birds on coming out of the egg without 

 exception eat insects, and nothing but 

 insects. Even those species which destroy 

 corn, always feed their young with cater- 

 pillars, grubs, and all the creatures which Reed Warbler. 

 are most mischievous to agriculture. All who have seen 

 young birds in the nest, know what an appetite they have. 



