Description of the Modifications of certain Orgaus. 633 



be doubted tliat the ancestors of the Genus Loxia had straight beaks 

 like the other FringüUdae, e. g. like the Genus Pinicola. The latter 

 have a thick stout l»eak, which they can use like a powerful i)air of 

 forceps. To the Loxias a poiuted and more slender beak has the 

 advantage of being able to be insinuated between the scales. This 

 elongation may have ariseii as a gratuitous Variation, subjected to 

 and intensified by natural selection , but the subsequent distortion 

 seenis to have been produced mechanically , by the bird itself. If it 

 had turned out to be harmful, natural selection would not permit it to 

 be transferred indefinitely, on the other hand the same factors will 

 elevate it to a permanent feature. 



Of course the side to wliich the first Loxia dislocated its under 

 jaw must have been almost, or probably quite, accidental, as the equal 

 numl)er of right and leftbilled specimens still indicates. 



In connexion with this is a point which requires to be considered. 

 If the distortion of the beak is inheritable, then its equally common 

 right and leftsided occurrence amongst the parents must tend to 

 abolish or to diminish its repetition in the oflFspring. The young bird 

 produced by a leftbilled male and a rightbilled female would, as we 

 should suppose, have a straight bill, and would have to acquire the 

 deflexion anew, unless it follows that parent whose Organisation has 

 been most strongly aifected by the distortion of the beak, be this 

 due to age or to this same parent's being the descendant of a series 

 of leftbilled birds. It is only fair to assume that generations of solely 

 leftbilled Crosbills will accumulate and inteusify the same tendency in 

 their oöspring. However we do not know if the difference in the 

 crossing of the beak is deemed by the Crossbills an obstacle to 

 pairing. The behaviour of birds in captivity would not settle this 

 question, and observations concerning the pedigree of nestling crossbills 

 have not come to my knowledge. 



2. The l)ill of the lYry-hilled Piover. 



The wry-billed Plover, Anarhynchus frontalis, is restricted to New 

 Zealand. In all the specimens hitherto known, the slender and sharply 

 pointed bill is invariably turned towards the right side. The right edges 

 of the preraaxilla and of the mandible are thin and strongly turned in- 

 wards so that the right and left sides are very non-symmetrical in section. 

 The left nostril and the groove, which is continued from it towards the 

 terminal third of the bill, remain in their original position, but the 



