THEIR REPRODUCTION (NESTS) 245 



we reach the crude ground -built nests of the 

 Waders, and kindred forms the simplest pro- 

 vision, consisting merely of a slight hollow with 

 a few bents and grasses carelessly arranged 

 therein. Reaching higher types of nests still, 

 we have, for example, the crude heaps of vege- 

 tation formed by the Grebes and Rails, the slight 

 structures made by the Pigeons, and so forth. 

 Then there are other species that appear to re- 

 quire a nest, but object to make one for them- 

 selves, and so annex the deserted home of some 

 other bird. Some species form a bed for the 

 eggs out of the refuse of their food ; others 

 secrete a salivary fluid, which soon hardens when 

 exposed to the air, and forms a nest layer by 

 layer. It is amongst the Passeriformes that we 

 find the most remarkable avine architects, pre- 

 senting an almost bewildering variety in the 

 form and structure of their nests. Of course it 

 would be utterly impossible to compress into 

 a single chapter sufficient material for a portly 

 volume. All that we can do is briefly to glance 

 at the most characteristic types and at a few of 

 the more remarkable structures. 



As might naturally be expected, we find a very 

 low type of architecture, or even an entire absence 

 of nest, amongst Ratitae Birds. The Ostriches 



