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OSCAR RIDDLE. 



writer ('07, '08), will find that Jones' plates and description 

 practically prove the existence of another variety of this same 

 defect ; in other words one may say that the modified region of 

 the down — the "quill" — is a variety of defect which we have 

 already recognized in other situations, but which here occurs in a 

 very uniform way — at a point near the end of the feathers of 

 the first plumage. The fact is, simply, that the defective region 

 falls so close to the end of the feather that it does not include 

 any of the shaft of the feather to which it belongs. 



There can be, I think, no question as to this interpretation. 

 The exact conditions met with in the defects or fault-bars already 

 referred to are to be found in the modified region of the down : 

 (1) In the modification or absence of barbules (Davies '89, 

 Jones) ; (2) in the occasional fusion of the barbs (Klee '86, 

 Davies, Jones) ; (3) in the diminished differentiation (Davies, 

 Jones) and growth (Davies) ; (4) in a defective development 

 between a more distal and a more proximal part of the same 

 feather (Jones). 



Now if the "quill region" of the down is the morphological 

 equivalent of the fault-bars (which are often produced " normally" 

 and which have been produced at will experimentally, at all 

 levels in the definitive feather), we should expect to find that the 

 two have the same or a similar cause. What is the evidence for 

 such a common cause ? What causes the production of " down " ? 



The Cause of the Modifications in the Down. 



It has been established beyond question that the several types 

 of fault-bars are produced by insufficient nutrition ; even the 

 variations produced in the available food-supply by the daily 

 fluctuations in blood-pressure was shown to be able to leave its 

 mark on feather structure (Riddle '07, '08). What now is the 

 evidence that reduced or insufficient nutrition is the cause of the 

 modification which occurs near the distal ends of the first feathers 

 of birds. 



The most highly modified region of the down, i. c, the " quill " 

 region, is produced in all cases so far as I am able to ascertain, 

 after and soon after the hatching of the bird. There are the 

 folio win sr reasons for a defective nutrition at that time : 



