Page:The Zoologist, 4th series, vol 4 (1900).djvu/281

Rh exactly with the rank which has been allotted to the specimen on the list, the latter being the outcome of the index received. As an instance, the first specimen on the list (Table I.), whose index is 144·4, has its longest remex shorter by 2 mm. than the corresponding one of No. 4, whose index of 141·4 is so much lower. The adult male No. 2, with its inferior index of 143·4, exceeds the young male No. 1 by 7 mm. in the longest primary, which measures 219 mm., and is the longest of all. These examples should suffice for showing the great individual variations obtaining throughout alike. Not more than five males exceeding the others by highest indices, also exceed them by having the longest measures for the seventh primary.

It is obvious, then, that as a means of diagnosis for the determination of sexes, a really characteristic difference in the lengths of the wing, or wing-feathers, found to exist in the species dealt with by Dr. Butler, has almost broken down in this particular case.

In addition to the indices on Table I., I have appended a further column, in which the length and the girth of the beaks are given. A comparison of these dimensions in their present order of indices—with which they in no way agree, any more than amongst themselves—does not exactly afford a ready means for discriminating between them. To achieve this latter purpose better, I have dealt with this character separately on Table II. by numbering the specimens according to the diminishing lengths of their beaks, but otherwise adhering to the plan adopted in Table I.

The arrangement of Table II. therefore shows that, apart from the differences in the colour of the plumage on the backs between adult males and females of this species, which does not enter into the scope of this work, a very good character for sexual difference, and of greater reliability than we have seen to exist for dimensions of wings, lies in the length of the beak.

With one exception only, namely, that of an adult male (No. 25 of Table II.), which is conspicuous by having an abnormally short beak (like the two young females at the bottom of the list), all females have their beaks inferior in length to the males; but nevertheless there is, as might be expected, great individual variation perceptible also in both sexes.