VOL. VII.] NOTES. 317 



In this connexion, it is well to bear in mind the fact (which 

 is well known*) that, in the nestling Crossbill the mandibles 

 show no sign of crossing. I saw various instances in proof 

 of this whilst counting the examples referred to above, but 

 all such were disregarded. It appears, however, that the 

 mandibles become fully crossed very soon after the young 

 bird leaves the nest. 



Another fact worth remembering is that the crossing is 

 confined entirely to the horny sheath of the mandibles, 

 their actual bony structure showing no signs of torsion, as 

 may be seen by anyone examining the skull of a Crossbill. 



These two latter facts afford evidence, no doubt, that 

 the crossing of the mandibles is a feature which has been 

 acquired by the species (and genus) within a very recent 

 period. Further evidence pointing in the same direction is 

 to be found in the fact (which I observed when examining 

 the specimens above referred to) that the bill (which is well 

 known to vary greatly in respect of length, size, and shape) 

 varies also very widely in respect of the extent of its crossing, 

 and this, to all appearances, independently of age, sex, and 

 locality. 



The fact that, in different examples, the- bill of the 

 Crossbill is crossed indifferently on either side affords, no 

 doubt, further evidence that the crossing of the bill is a 

 recently-acquired character. At the same time, it is 

 by no means clear why examples having the bill crossed 

 on either side should occur in such extraordinarily equal 

 numbers as my figures seem to show that they do. One 

 wishes it were possible to make observations to ascertain 

 whether or not the crossing of the bill is what is termed 

 a " Mendelian character." Probably, however, it is too 

 recently acquired to be such. 



The exact opposite of all this is, no doubt, the case in 

 that extraordinary bird the Wry-billed Plover [Anarhynchus 

 frontalis) of New Zealand,! which has its bill congenitally 

 asymmetrical, even from the nest, both mandibles being 

 always twisted dextrally, this peculiarity affecting not merely 

 the horny sheath, but the actual bony structure of the bill. 

 The bird is said habitually to run round stones — always 

 from left to right (dextrally) — searching for food beneath 

 them. In its case, no doubt, the twisted bill is a very 

 ancient character. Miller Christy. 



* See, for example, Saunders {Manual, p. 194, 1889) and Newton 

 (Diet, of Birds, p. 115, 1896). 



t See Buller's Birds of N. Zealand, II., p. 9 (1888), and Suppl., I., 

 p. 177 (1905). 



