2 86 Journal of Travel and Natural History 



sive hens. Therefore, the cock Pheasant is assumed to have 

 begun originally from a dull colour. But the hen, on the con- 

 trary, has " attained" to her dull colouring by the continual 

 destruction of preceding hens. Therefore, the hen Pheasant is 

 assumed to have begun originally from a brilliant colouring. Of 

 course this is a theory of such admirable elasticity that it is cap- 

 able of being adapted to any facts whatever. If they don't suit 

 the theory, when read straight forwards, it is only requisite to turn 

 them round and read them backwards, and one way or another 

 they can always be made to fit. 



I wish, however, to observe that in my opinion it is not possible 

 to assign a reason any more than a physical cause for many of the 

 peculiarities of nest-building. Take the case of the Blackbird and 

 the common Thrush — birds closely allied, and building very much 

 in the same situation. Why should the Thrush always line her 

 nest with mud, and the Blackbird always with fibrous roots ? No 

 answer can be given. In like manner may other species, closely 

 related in structure, in habitat, in food, have fixed and persistent 

 differences in their architecture. I am more and more convinced 

 that variety, mere variety, must be admitted to be an object and 

 an aim in Nature ; and that neither any reason of utility nor any 

 physical cause can always be assigned for the variations of instinct. 



I would, however, suggest to Mr Wallace that one great object and 

 use of domed nests, and also of many nests being made in holes, 

 is one which has no connexion whatever with concealment, or 

 consequently with his theory. That use is the very obvious and 

 simple one of the better conservation of animal heat in cases where, 

 from the extreme smallness of the bird and of its young, special 

 provision has to be made for this purpose. It is at least remark- 

 able that in our own country the most perfectly domed nests are 

 made by the smallest birds, and these, too, by birds whose colour- 

 ing requires no special precautions on account of its conspicuous- 

 ness. So far as sombre and neutral tints are concerned, no birds 

 could more safely sit upon open nests than the golden-crested 

 Wren or the common Wren, or the long-tailed Tit, or the Willow 

 Wrens. But the very diminutive size of all these birds, and their 

 delicate organisation, do require that special j)rovision should be 

 made for the retention of warmth, and for i)rotection from wet as 

 well as from cold. This is the reason why the birtls should make 

 domed or covered nests. I have no doubt whatever that the same 

 reason applies in numerous other cases, wherever the conditions 



