cause of production of "down." \j\ 



Rate of Growth in Relation to the Kind of Feather 

 Structure Produced. 



It is well known that "down" — i. e., the distal plumulaceous 

 tip of the feather — and the plumulaceous proximal parts of pen- 

 naceous feathers are similar as regards their appearance and 

 texture. They all possess long, slender barbules — usually 

 without hooked barbicles. So far as my observation goes all 

 have the barbules set rather widely apart, and have a fluffy 

 appearance. Since Jones has shown that the " down is the 

 plumulaceous tip of the first definitive feather"; and since in all 

 typical pennaceous feathers we have also a plumulaceous proximal 

 end of the feather, what does it mean in the development of the 

 first feather that two plumulaceous regions are produced with a 

 pennaceous region between ? 



The writer is convinced that the type of feather structure pro- 

 duced is somehow quite definitely correlated with the relative 

 rate of growth at which the various parts of the feather are 

 developed. The following facts and observations are submitted 

 in favor of this view : 



1. That the " down " is of slow growth is proved by the works 

 of several writers — Studer '73, Klee '86, Davies and Jones among 

 others — who have shown that in various birds the down begins to 

 develop from the fifth to the eighth day (in the egg) and continues 

 usually fifteen to twenty days, or longer. This, when compared 

 with the growth which succeeds it is obviously very slow. 

 D wight ('00) also notes that " during the early days of the 

 newly-hatched chick (passerine birds) feather growth is com- 

 paratively slow, but shortly it proceeds with marvelous rapidity" 

 (p. 99). 



2. If a feather from a juvenal plumage is taken for considera- 

 tion, it may be said that that part of the feather which lies between 

 the " down " (plumulaceous) and the basal plumulaceous portion 

 of the feather, is grown (rectrices or remiges of ring-dove) at an 

 average of more than twice the rate of either of these extremities. 



The slow rate of growth of " down " is self-evident. The fol- 

 lowing measurements in mm. of a rectrix of the ring-dove are 

 given to show that the above statement is true as applied to the 

 proximal plumulaceous growth. 



