No. 25— j NOTES ON FEATHERS* 8f8 



elusion by no means unreasonable, as otherwise they are useless, 

 and further a single glance would show that this portion of the 

 feather is closer, and hence warmer, than if these sub-web-shafts 

 were absent. Supposing a iveb shaft is removed from the same 

 feather — Woodpecker's — and placed under a microscope of some 

 power, the sub-web-shafts exhibit a series of joint-like markings 

 of a more or less modified character. See Figs. 2,3,4, 5, & 6. 



This modification is of very considerable interest, as the 

 conclusion that I have arrived at, after carefully examining a 

 large series of Ceylon birds, is, that they are modifications of 

 an aboriginal form, which I have ventured to illustrate. 



I have drawn my conclusions from the fact, that at remote 

 periods of time, it is but reasonable to conclude, that birds 

 required a closer plumage than at present, in order to endure 

 a colder temperature than now upon the earth, and to bring 

 about that end a further addition to the sub-web-shaft would 

 render most material assistance. I am confirmed in this view 

 by the fact that some of our high flying eagles, such as Sjnzaetus, 

 possess a spine upon the sub-iveb-shaft, that can be considered 

 as a modified filamentous process, just as the sub-iveb-shaft is 

 itself. 



The conclusion then to be drawn is that those represent- 

 ing the series Fig. 2, are of a much older formation than the 

 series Fig. 4 through process of modification, through disuse. In 

 like manner the forms up to Fig. 6 can be traced up to what was 

 probably the aboriginal form, Fig. 7. I am inclined to believe 

 that any of the forms may be traced through variation and 

 modification to the form Fig. 7, which through long ages of 

 disuse forms the present modified structure. If then, this view be 

 correct — and I am unable to see cause for any serious objection 

 to it — the course of modification may be traced as represented 

 in Fig. 8, from the aboriginal form to the present, as shewed 

 by the dark lines, and the dotted lines, which bear a strong com- 

 parison with Fig. 7, or with Fig. 6, which last is an existing 

 form. 



I consider that by this peculiarity of structure we shall be 

 able to trace the relative ages of existing forms of birds, which 



