346 Coves, (iiifkcs Helio-olai/cf. [ f,^"J^ 



This conclusion concerning "the way of the eagle in the air" 

 is identical with that ascribed to the old Hebrew ornithologist, 

 who had a great reputation for sagacity, in spite of his compre- 

 hensive connubialities ; and may be aspired to by some of the 

 present gentile generation. 



Yet one other chapter of Giitke's remarkable book should not 

 be passed without remark in the present review. This is in a 

 diflerent field of research, as it treats of changes in the coloration 

 of plumage without the loss or gain of any feathers. To this 

 phenomenon, for which I lately coined the word aptosochromatism, 

 Schlegel called particular attention in 1852, and the novelty of 

 his views excited much attention. The subject is better known 

 now, but is far from being exhausted, and Giitke's contribution to 

 its elucidation is extremely valuable. The two main factors in 

 the case, namely, variation in pigmentation and alteration in 

 texture and shape with wear and tear, are understood ; but the 

 processes are more complicated than would appear at first sight, 

 and there are several ways in which the observed changes may 

 be brought about, in different species, in the same bird at different 

 seasons, in different feathers of the same bird, and finally, in 

 different parts of the same feather. Some of the modes in which 

 fresh pigment may be deposited in and spread through a feather, 

 and then be modified or withdrawn, are curious, and not less so 

 are the ways in which an optical effect is produced by a sort of 

 exuviation in the feather itself, aside from any such simple process 

 as the wearing away of a tip or an edge — in other words, it is a 

 vital rather than merely mechanical matter, which is probably 

 much more concerned than we are fully aware in freshening 

 coloration. Aptosochromatism would not seem to be a subject 

 of special ditffculty, or one requiring particular training for its 

 successful study. It is simply a matter of precise and patient 

 examination of a large amount of material, and offers an inviting 

 field of research, in which some bright young ornithologist might 

 win enviable laurels. 



