bottom of streams as he searches for caddis-worms 

 or insects, and his breast feathers are dense and 

 impervious to water. The Rook may be known 

 from the Crow by the absence of feathers on the 

 beak ; they are worn away through his habit of 

 digging in the ground for food. In the young bird 

 they are still there, and to make sure whether you 

 have a Rook or a Crow you have to look at the 

 inside of the mouth ; in the Rook, it is deep flesh- 

 colour, in the Crow, much paler. 



Though some of these distinctions may appear 

 trifling and insignificant, yet it is impossible to study 

 classification without learning a great deal that is of 

 real interest. There emerges, for instance, the very 

 interesting fact that most birds, which for their size, 

 lay large eggs, lay them on the ground, and that 

 their young when hatched are covered with down, 

 able to run at once or in a few hours, and, before 

 long, to fend for themselves. There seems at the 

 same time to be another principle at work side 

 by side with that just explained — namely, that the 

 eggs of a bird which lays a great number must be 

 small, in order that she may be able to cover them. 

 Certainly many of those whose eggs are largest lay 

 only one, or at any rate very few, and their young are 

 highly precocious. 1 No infant creature is more inde- 

 pendent than the Maleo, a bird about the size of a 

 small Turkey, native in the Island of Celebes. The 

 mother buries her wonderful egg (weighing 8J to 9J 

 ounces — i.e., about Jth of the weight of a mature 



1 See the article on " Eggs " in Newton's Dictio7iary of 

 Birds. 



