THE CAUSE OF THE PRODUCTION OF "DOWN" 



AND OTHER DOWN-LIKE STRUCTURES IN 



THE PLUMAGES OF BIRDS. 



OSCAR RIDDLE. 



A recent paper ('07) by Dr. Lynds Jones makes clear the 

 morphological relations of " down " and definitive feathers. 

 Jones' work, some experimental results already reported by 

 the writer ('07, '08), together with some hitherto unpublished 

 data bearing on the physiology of avian plumages, now enable 

 us to make some fairly definite statements concerning the causes 

 which lead to the production of " down." A number of obser- 

 vations and experiments on the relations which exist between the 

 rate of groivth and the character of the feather structure produced 

 — pennaceous or plumulaceous — also suggest some interesting 

 conclusions. It will be shown later that results from these 

 various angles of approach center about a common point. 



Jones' studies demonstrate positively that "the first down and 

 its succeeding definitive feather are produced by one continuous 

 growth, and therefore cannot be regarded as two distinct feathers. 

 The first down is the plumulaceous tip of the first definitive 

 feather" (p. 17). 



This writer has however failed to homologize the modified 

 region which connects the two parts of such a feather with any- 

 thing already known ; and, apparently he has not perceived the 

 actual cause of this modification. To point out the homologies 

 and state the cause of the various modifications found in the 

 down ; to show how the " down " and the plumulaceous proximal 

 parts of pennaceous feathers are related to their rate of growth ; 

 and in connection with this latter point to put forward a general 

 theory of the significance and relations of all plumulaceous and 

 pennaceous feather structures, is the purpose of the present paper. 



Homologies of the Modified Region of the Down. 



Anyone who is familiar with the several forms of feather defects 

 or fault-bars which have elsewhere been fully described by the 



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