172 



OSCAR RIDDLE. 



Table I. 

 Showing Rate of Growth of Rectrix of Ring-Dove {Turtur nsorius). 



At the point indicated with the star (*), i. e., at about 95 mm. 

 from the distal tip of this feather, it is found that the plumulaceous 

 formation begins. At first only those barbs which lie in the germ 

 opposite to the shaft are affected ; but as growth proceeds — and 

 as the rate of growth diminishes — more and more barbs become 

 affected. 



After having watched the rate of growth of many feathers in 

 chicks and doves only to find that the plumulaceous part always 

 begins at the point of, or after, a considerable falling off in this 

 rate of growth, one is tempted to the conclusion that in these 

 feathers the two kinds of feather growth, plumidaceous and pen- 

 naceous, are merely expressions of slozv and rapid growth re- 

 spectively. 



It is, I think, moreover, quite certain that for many birds the 

 general rule can be laid down that those feathers which as a 

 whole grow slowest have the greatest proportion of plumulaceous 

 growth. 



One is led by such considerations to inquire whether all strictly 

 plumulaceous feathers are of slow growth. I know but little of 

 these conditions from personal observation, but the known facts, 

 in so far as I have been able to ascertain them, are in harmony 

 with this view. 



It is stated that the ostrich plumes grow at the rate of one inch 

 per week. For such feathers of such birds this is indeed a slow 

 rate — only about 3.5 mm. per day; whereas a little, newly 

 hatched ring-dove will grow remiges and rectrices at from 5 to 7 

 mm. per day. I feel confident that it will be found that all 

 plumulaceous feathers are grown at a relatively slow rate. 



The aftershaft (hyporhachis) which is found in many feathers 

 is another plumulaceous formation and like the others is of slow 

 growth. It seems to me highly probable that a closer study of 



