320 MR, J. I;, BONHOTE ON THE [June 18, 



on the cross-bars feathers are found of all shades from deep orange 

 to yellowish white. 



These remarks, although somewhat beside the point, have been 

 inserted as showing one of the many causes by which the develop- 

 ment of the pattern in the feather would tend to be altered and 

 modified, in the young birds no less than in the adults, to such an 

 extent as to overturn at first sight the theory contained in this paper. 



It is, perhaps, needless to add that these are the patterns on 

 which the large majority of species are based; they have in reality 

 but little in common with the markings on a feather itself, about 

 which this paper is written. Other causes such as protection, 

 vigour, and adornment, all play a part in the general pattern and 

 markings on the birds ; but, leaving the modification caused by all 

 these as far as possible out of consideration, let us look at a few 

 examples from widely-spread Orders, and see to what extent the 

 process of evolution as set forth above is borne out by the 

 facts. 



In the young Peregrine the back is of a uniform brovt-n, 

 with a light edging ; after its first moult the feathers are clearly 

 referable to the type in fig. 6, while those on the tail are of a 

 similar type, but with the tips of the bars ([uite joined up in an 

 exaggerated form of fig. 7. In the adult bird the bars on both 

 the back and the tail are complete. On the pattern of the breast 

 it is unnecessary to enlarge, for it is similar to that of the Sparrow- 

 hawk. It is worth noting, however, that while the back and breast 

 have undergone similar changes, the back has become considerably 

 darker, having been presumably modified for protective purposes. 

 The Kestrel, on the other hand, offers an example in which, in 

 the young bird, the tail and the back have complete bars which are 

 afterwards to a great extent lost, while on the breast the bars are 

 either very incomplete or we have merely the very early form of 

 longitudinal stripe. This is but one case of a very common 

 phenomenon to which I shall have occasion to refer again, namely : 

 that when the upper and under sides of the plumage show different 

 stages of evolution, the upper parts are generally the most 

 advanced. 



Before leaving the Hawks, where similar observations may be 

 made on most species, we might look at the back and tail of the 

 adult male Sparrow-hawk. At first sight the whole of the upper 

 surface will appear self-coloured, but a closer look will reveal two 

 or three darker patches on the tail showing the last remnants of 

 the bars. It will then seem that in this case the tail has not 

 advanced so quickly as the body-feathers in its rate of evolution. 

 If, however, the feathers of the back be raised up, we find that these 

 feathers are in reality a modified form of the type shown in fig. 8, 

 with the terminal marking relatively very large and quite concealing 

 the white base of the neighbouring feather. With regard to the 

 Strigidse as a group, I have not had time or opportunity to go into 

 the matter very thoroughly ; but, in those I have examined, the 

 patterns lend themselves to classification as in other groups, 



