20 DEVELOPMENT AND HEREDITY. 



gence comes to the aid of instinct ; and thus instinct 

 and intelligence are most intimately connected. 



The observation of the nesting of birds shows 

 further how closely instinct resembles the result of 

 intelligent experience. The common American black- 

 bird arrives in the north in the cold season, before 

 the deciduous trees have put out their foliage, and 

 accordingly the blackbirds frequent the pines, 

 spruces, balsams, etc., enjoying their shelter for 

 nests, and their dry twigs for building material. 

 The robin arrives in the north during the wet and 

 muddy weeks of spring, and builds its nest largely 

 of mud. The bobolink comes when the meadow- 

 grass is high, and finds security for its nest under 

 the tall grasses. The yellow-bird arrives when the 

 willows are scattering their downy seeds, and uses 

 these and other cotton-like material for its nest. 

 The several methods of the nesting habits of these 

 birds are so invariable, that they may, without hesita- 

 tion, be classed as instinctive, and yet we can hardly 

 conceive of this remarkable adaptation to circum- 

 stances as having originated in any other way than 

 by experience and intelligent choice of that which was 

 the most suitable. If it were due to an undirected 

 variation, we ought to find some trace of such varia- 

 tion ; but we do not hear of such cases as blackbirds, 

 robins, and bobolinks failing to rear their young 



