30 THE ZOOLOGIST. 



advances, the edgings of these feathers in both sexes wear off 

 by abrasion. 



A change somewhat similar to this is found in the Great 

 Northern Diver (Colymbus glacialis), and probably in other 

 species as well. It is comparatively difficult to procure an 

 individual of C. glacialis in full winter plumage (as described by 

 Mr. Cecil Smith in his 'Birds of Somerset,' p. 540), which 

 resembles somewhat that of the immature birds; for as soon as 

 the feather is formed, or even while growing, it commences, by a 

 change of colour in the feather itself, to assume the distinguish- 

 ing features of the breeding plumage for the following year ; it is 

 therefore possible to find in the same individual worn feathers 

 of last year's breeding- dress, new feathers that have not yet 

 changed but are of a uniform bluish grey, and those which have 

 already by change of colour assumed the white spots and dark 

 ground of the next year's breeding dress. 



Returning to the Corncrake, the similarity of the moult in 

 both sexes, with the subsequent although practically simul- 

 taneous assumption of the breeding plumage by the male, tends 

 to show that, in this instance, the reason of the moult is not for 

 the assumption of the breeding dress, for in that case it ought 

 only to be undergone by the male. The evidence before us 

 seems to point to the fact that the moult has no connection with 

 the colour-change, but is due to some ulterior cause of which we 

 are at present ignorant. 



The method by which this change of colour is brought about 

 is very hard to determine, but the following notes of a micro- 

 scopical examination of feathers in process of change, taken 

 from a living bird a few minutes before examination, may be of 

 interest. 



If a feather be taken which is fully grown and in process of 

 changing, and be microscopically examined by transmitted light, 

 with a low power of about 66 diameters (with a higher power it 

 was difficult to get satisfactory results by reflected light), we find 

 that, whether the part of the feather be blue or brown, there is 

 absolutely no difference in the arrangement of the rami or radii, 

 and that both are opaque and show no colour. If these same 

 parts be then examined by reflected light, the brownish part 

 appears dull, the rami and radii being both of a light-brown 



