110 The Naturalist in Siluria. 



from a tree in the Forest of Dean. It is of rounded 

 form, and roofed, with side entrance, its bulk being about 

 that of a child's head ; and, as with the nests of most 

 birds, it is double-walled, having an outside layer and 

 lining. The former is composed of coarse moss, with an 

 admixture of sheep's wool, and, more sparingly employed, 

 broad strips of bark, the thin outer epidermis of young 

 oaks. The material of the inner wall or lining is alto- 

 gether different, consisting exclusively of the under or 

 sap-bark of the oak, split into fibre-like strands, some 

 of them fine as sewing-thread, their ragged ends and 

 edges showing evidence that the splitting had been done 

 by the animal's teeth. Now, to procure this material, 

 and hackle it into the required condition, must have cost 

 the squirrel, or pair of squirrels, a considerable amount 

 of labour, independent of the task of construction. The 

 question, therefore, suggests itself, why this extra toil 

 when other substances, seemingly equally suitable, were 

 to be had in plenty around ? Just by the tree from 

 which this hut was taken there grow grasses of several 

 species, some of them slender-bladed as the bark fibres 

 used in its lining, and these could have been had with 

 but the slightest exertion of strength or teeth. The 

 employment of some preferred material in the construc- 

 tion of their nests is one of the most singular habits, or 

 instincts, of birds, and one still hidden among the arcana 

 of nature. But not less singular that squirrels, also 

 nestbuilders, should show a like instinct, for of other 

 huts I have examined the materials were the same. 



