There are some mammals among whom the sexes do not differ appreciably in size and strength, and very little or not at all, in coloration and ornament. Such is the case with nearly all the great family of rodents. It is also the case with the Erinaceidae, or at least with its typical sub-family of hedgehogs.[33] Even among birds, where the sex instincts have attained to their highest and most aesthetic expression, we find some large families--as, for example, the hawks--in which the female is usually the larger and finer bird.[34] Thus the adult male of the common sparrow-hawk is much smaller than the female, the length of the male being 13 ins., wing 7.7 ins., and that of the female 15.4 ins., wing 9 ins. The male peregrine, known to hawkers as the tiercel, is greatly inferior in size to his mate. The merlin, the osprey, the falcon, the spotted eagle, the golden eagle, the gos-hawk, the harrier, the buzzard, the eagle-owl, and other species of owls are further examples where the female bird is larger than the male. Among many of these families the female birds very closely resemble the males, and where differences in colour and ornament do occur, they are slight. A further point of the greatest importance to us requires to be made. Wherever amongst the birds the sexes are alike the habits of their lives are also alike. The female as well as the male obtains food, the nest is built together, and the young are cared for by both parents. These beautiful examples of sex equality among the birds cannot be regarded as exceptions that have arisen by chance--a reversal of the usual rule of the sexes; rather they show the persistence of the earlier relations between the female and the male carried to a finer development under conditions of life favourable to the female. I will not here say more upon this subject, as I shall have to refer to it in greater detail when we come to consider the sexual and familial habits of birds. I will only add that in their delicacy and devotion to each other and to their offspring, birds in their unions have advanced to a much further stage than we have in our marriages. These associations of our ancestral lovers claim our attentive study. II.--_Two Examples--The Beehive and the Spider_ "At its base the love of animals does not differ from that of man."--DARWIN.