SEXUAL DIFFERENCES IN WING FEATHERING. 253 



exactly with the rank which has heen 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 corre- 

 sponding 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 obtain- 

 ing 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 deter- 

 mination 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 par- 

 ticular 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 diminish- 

 ing 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 abnor- 

 mally 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. 



