=Protective Construction of Nests.=--It is surprising again to find Darwin, in arguing that few British birds build covered nests to protect themselves against the conspicuousness of their own colours, citing the Dipper as an instance of this. But what about the white breast of this bird, which marks it out at long distances against the dark rock or water? Again, her pure white eggs are manifestly a source of danger, more conspicuous even than the bird. It must not be supposed I overlook another important feature in the covered nest of this bird, which is, however, subservient to the bird's desire to hide her white plumage and eggs, which renders it equally preservative in character. The bird generally builds near a waterfall, often quite behind, undoubtedly for the safety this situation affords, and she is not only obliged to construct a covered nest, but one which must keep out the constant dripping of water percolating through fissures in the rock. The construction of this nest even cuts off the chance of a stray splash of water finding its way to the eggs or young during the parent bird's absence, by the peculiarly ingenious entrance she makes to her little home. Still further, where birds are conspicuous in colour they either build covered nests, or place them in such situations as afford safety, and are thus equivalent. For instance, the Woodpecker, Kingfisher, and Magpie, the two former having a double object in the selection of a situation, firstly their own eminently brilliant colours, and secondly their pure white eggs. The latter building a covered nest of such materials as thorns, seems to point to a strategic planning against the immorality of the family to which he belongs. =Periods of Incubation and their Utility.=--The Duck family all lay eggs white, or nearly approaching it, and take the precaution to cover them carefully on leaving the nest. Some naturalists have been of opinion that this is to prevent an undue escape of the heat generated by the parent; however, I am unable to find any observations to prove that these birds leave their eggs for feeding purposes longer than any others that hatch their young in three weeks. Neither does it appear that they transmit heat better or worse than birds of entirely different habits, for it takes a Fowl four weeks to hatch a Duck's egg, and a Duck will on the other hand hatch a Fowl's in the normal time, three weeks. It appears that the period of incubation is regulated with a great amount of precision by the contemplated habits of life, the difficulties to be overcome, and dangers to be endured, as the following facts show:--