Racket Feathers

Abstract

YOUR able reviewer of Meyer and Wiglesworth's “Birds of Celebes” (NATURE, April 26), criticising the arguments used to account for the formation of the racket tail feathers of the parrot, Prioniturus (as an inherited effect of mechanical attrition on objects against which the tail is liable to be brushed—boughs, walls of nesting-hole, &c.), asks the pertinent question, why so few exposed feathers, such “as the external rectrices and remiges of all birds, and specially the lengthened feathers of wedge-shaped tails (Dicrurus) are neither bare nor racket-shaped nor incipiently so.” The insignificant length of the outer rectrices of Dicrurus perhaps safeguards them; when these feathers are longer, as in the closely-allied Bhringa and Dissemurus, they are racket-shaped. As to the remiges and rectrices of birds generally, one feather overlies and to a great extent protects the next; but still, the outer webs are always very much narrowed in the outermost and most exposed feathers, less narrowed in the next, and so on till in the middle of the wing and tail (where they are well protected on both sides) they are not narrowed at all. But, while normal wing and tail feathers are exposed to attrition on one web only, long feathers standing well out from the rest are liable to have the web frayed on both sides of the shaft as far as they project beyond the other feathers, and to some extent where they rest upon the other feathers through friction against the latter. It is assumed that at some period earlier in the history of the race these elongated feathers were of the usual simple shape, but they are now known to issue from the follicles displaying peculiarities which are often much the same as those obtained by scraping an ordinary feather with a knife—namely, if the shaft is stiff and not very long, a small terminal spatule is formed (as in Prioniturus, Parotia); if the shaft is long and weak, a large spatule (as in Tanysiptera, Loddigesia). A difficulty, perhaps, to the acceptance of the theory is its apparent consequence—that epidermal (in a sense, dead) structures, like feathers, possess the power of transmitting: mutilations to posterity. For my own part, I think that the modification of shape of the feathers is communicated to the sensitive tissues (much in the same way as the shape of a stick placed in the hand of a blind man is comprehended by him after touching other things with it), and that a corresponding physiological adjustment is made and gradually inherited. The result is probably not an exact recapitulation of the mutilation, but it sometimes appears to be very nearly so.