XX 



from a vestigial ^^ plume " in one group of birds to a well- 

 developed " penna '"' in another^ appears to present at first 

 sight a parallel analogy to aquiutocubitalism. But the varia- 

 tion in the texture of the underlying feather, from a pluma- 

 ceous to a pennaceous state^ in the case of the carpal covert, 

 suggests a different theory as to its value, especially as the 

 underlying feather referred to lies on the dorsum oi^ the 

 ala membrana, instead of on the ventral side of the latter, 

 as is the case in the aquintocubital ventral major covert. 

 This was fully confirmed by the examination of a Great 

 Black-backed Gull in a state of moult ; and it is evident that 

 in this family the underlying feather above alluded to, which 

 is so generally vestigial, becomes a fully developed and truly 

 pennaceous feather, exceeding both in length and strength 

 the carpal covert itself. Another important fact in the case 

 of the Black-backed Gull (and one which, in my opinion, is 

 quite decisive as to the value of the lower of the two carpal 

 feathers) was that both the carpal covert and its pennaceous 

 remex were moulting under exactly the same conditions as 

 the two preceding metacarpals with their coverts, and were 

 behaving in ])recisely the same manner. There can be no 

 doubt, therefore, as to the origin of the carpal covert, and it 

 must be looked upon as a normal upper major covert, of 

 which the remex has either become reduced to a vestigial 

 plume or exists only as a dwarfed pennaceous feather. 



The suppression of tlie remex in the case of the 5th 

 cubital is patent, wdiile the suppression of the remex on 

 the wrist-joint (still, as we have seen, in a transition staac 

 of annihilation) is not so evident. Being certain in my own 

 mind as to the accuracy of the facts disclosed, it occurred 

 to me that further analogies, based upon similar principles, 

 might be traced in following up the series and divisions of 

 tlie fore limb of the bird. In this attempt I have been 

 greatly assisted by the accurate and very forcible descriptions 

 given by ^Ir. W. P. Pycrafc in his paper read before the 

 Leicester Literary aud Philosophical Society, and printed in 

 their Transactions, vol. ii. pt. 3 (1890). Here he corrects 

 the erroneous views of many authors on the subject of the 



