CAUSE OF PRODUCTION OF "DOWN. I 73 



the nutritive conditions in this region of feather- germs would 

 reveal the reason for the presence of this feather-accessory in 

 some plumes and its absence in others. 



The true quill (calamus) also shares this slow growth of the 

 proximal end of the feather. Indeed it is in the quill that we 

 find the slowest rate of growth to be met with in the whole length 

 of the feather. I am inclined to "explain " the quill as the type 

 of feather formation which results from nutritive conditions which 

 become slowly and progressively poorer ; this in turn is able to 

 almost completely stop growth and cell-division, but affects the 

 process of cornification, i. e., keratin formation, to a much smaller 

 extent. It seems to me, too, that our knowledge of feather- 

 growth (quill-formation) in the Japanese fowls, particularly the 

 results of Cunningham's ('03) experiments, and many other facts 

 support this conclusion. Neither the position nor the presence 

 of a quill is " predetermined " in the feather, but both of these 

 are merely marks left along the course of the ebbing tide of a 

 greatly diminished feather nutrition. 



The fact that plumulaceous structures do not show the maxi- 

 mum of growth and differentiation (e. g., weaker barbs, and bar- 

 "bules without hooklets) together with the observation that such 

 regions occasionally result from under-feeding (Fig. i), would 

 seem to lend weight to the view that such regions or such entire 

 feathers are grown under nutritive conditions considerably below 

 the optimum. 



It should be remarked that if the view here put forward is cor- 

 rect it would lead us to expect a pretty general occurrence of 

 growth-marks on all feathers which are growing at the time of 

 hatching and soon thereafter. Such marks seem not to have 

 been reported for the rather extraordinary first feathers of the 

 Anserine birds. My own observations on this plumage of these 

 birds are too meager to mention, but it seems quite probable that 

 such marks are much less in evidence there — if they exist at a 1 

 — than in most other birds. It is conceivable, however, that 

 the young of these birds have a greater quantity of egg-yolk left 

 for their first day or two after hatching ; or that they have a con- 

 siderable store of available fat in their bodies ; or yet another 

 means of tiding them over the " critical period " which in these 



