vir. THE SWALLOW'S NEST. 



123 



rocks, or in holes of banks and walls. The nest varies 

 in construction according to the purpose which it serves. 

 If it is used only for incubation, it is of the simplest 

 structure, being often a mere hollow scratched in the 

 bare ground without any regard to form; if, on the 

 other hand, it is used both for incubation and sheltering 

 the young, it is shaped with much care and skill, an ex- 

 quisitely rounded cup frosted with lichens, and packed 

 with green moss, and lined with the softest down and hair, 

 looking as if it had been turned on a potter's wheel. 

 These gradations in nest architecture harmonize with the 

 differences in the bodily structure of birds and in their 

 habits and modes of life. We recognize a close family 

 resemblance between the nests of birds belonging to the 

 same species or order, although occasional differences 

 may be detected when the situation is peculiar and the 

 choice of materials limited. 



It is supposed that the nests of birds show no pro- 

 gress during the long period they have been under the 

 observation of man. The nest of the bird is commonly 

 regarded as the equivalent of the matrix in other 

 creatures ; and the processes which go on unseen and 

 unconsciously in their internal economy, are carried on 

 externally by the bird, visibly and consciously, by an 

 instinct which corresponds with the physiological law in 

 the former case. Hence the product in the one instance 

 is supposed to be as fixed and unalterable as in the 

 other. But acute observers have noticed, nevertheless, 

 that the faculty of nest-building is capable of education, 

 and that the first attempts of young birds are much more 



