290 MISS NEWBIGIN ON THE [Feb. 18, 



tion of the ordinary metallic contour-feathers of most Humming- 

 birds has been accompanied by a reduction of this terminal band 

 in width and in the individual barbules forming it, a large increase 

 of pigment in the laminas of the barbules forming the blackish- 

 grey part of the feather in Phaethomis, and a specialization of the 

 barbules of this region, of which the most obvious result is the 

 shortening of the filamentous portion and its inclination to the 

 lamina. In the feathers of the patches of especial brilliancy these 

 changes have been carried further, and have been accompanied by 

 a shortening of the feather and rounding of its tip, and a change 

 in the angle of insertion of the barbules. The changes in the 

 wing-quills seem to have been of a simpler description, and to have 

 been chiefly accompanied by a specialization of the lamina. 



As to the meaning to the individual of this progressive change, 

 one suggestion may be hazarded. The Humming-birds are espe- 

 cially characterized by their power of flight. Now of the many 

 correlated variations which must occur during the gradual improve- 

 ment of the power of flight, an increased development of the 

 lamiua and of cilia and booklets is likely to be important. It is 

 therefore perhaps not unreasonable to suppose that the metallic 

 colours of Humming-birds are due to a persistence in the same line 

 of variation which produced their powers of flight. If Kolliker 

 (" Die Entstehung des Pigments," Zeitsch. f . wiss. Zool. vol. xlv.) is 

 right in his belief that the foi'mation of pigment is connected with 

 the blood-sj'stem, it is quite comprehensible that an increase in 

 structural specialization should be accompanied by an increase in 

 the amount of pigment. It might be objected that the Swifts, 

 which are probably nearly allied to the Humming-birds, have also 

 great powers of flight and yet do not show metallic colours. In 

 reply to this objection, it may be said that it is generally admitted 

 that Humming-birds have few enemies, and that therefore variations 

 migjit occur in them unchecked which would possibly lead to 

 elimination in other forms. A more important objection is that 

 the wings do not usually show metallic colour : it seems iuipossible 

 to suggest a reason for this beyond the simple fact that the wings 

 seem to be slow to vary in colour. It will be noticed that, in the 

 especially brilliant patches, the extreme closeness of the connection 

 between the adjacent barbs is a variation in the direction of the 

 ordinary condition of the feathers of flight. 



The course of the development of metallic tints in Sun-birds offers 

 many points of contrast to that just described for Humming-birds. 

 If we take (PI. XII. fig. 22) one of the ordinary contour-feathers 

 of a non-metallic form, such as a female of a species of Glnnyris, 

 probably C.jugularis, it will be found that it presents considerable 

 resemblance to a corresponding feather from a " hermit" Humming- 

 bird. Thus it consists of a basal downy region, a mid-regiou 

 pigmented with brownish black, and an apical region with discon- 

 nected diverging barbs, usually of a dull olive colour. Beginning 

 with such a feather, the development of metallic colour is 

 accompanied by an increasing predominance ajnd pigmentation of 



