GENESIS OF FAULT-BARS IN FEATHERS. 345 



Of greater interest than these known cases of epidermic re- 

 sponse to nutrition are, in my opinion, similar responses which 

 have as yet not been recognized in other tissues and organs. The 

 constantly observable daily effects on feather structure of only 

 slight "normal" daily reductions of nutritive conditions in the 

 bird has fully convinced me that similar, and longer starving 

 periods, and seasons of hibernation "normally" passed through 

 by many animals, cannot but produce definite and lasting marks in 

 many of the tissues and organs of these animals. (The effects may 

 often, indeed, be so slight as to escape observation even with the 

 microscope, but this does not negative their existence.) The 

 writer believes that from this standpoint it would be very desirable 

 to study the formation and growth of many tissues and organs ; 

 particularly such lamellar structures as ivory tusks, bone, certain 

 ova, pacinian corpuscles, and doubless many others. 



Feather Growth. 



It was recognized at an early stage of these studies that accu- 

 rate data on the region and rate of growth in the feather must be 

 secured. Very few of the numerous writers on feather structure 

 and development seem to have concerned themselves with either 

 of these problems. The region of growth has of course been 

 indicated in a general way (most definitely in "down") but its 

 very restricted limit has not, heretofore, I believe, been sufficiently 

 emphasized. The figures of Davies, 1 Haecker ' and the still 

 better ones of Strong 1 are, however, suggestive of it. Some ob- 

 servations and experiments on the rate of growth in chicks and 

 doves are reported here. 



The Region of Feather Growth. — A study of the growing tips 

 of remiges and rectrices of ring doves, and of the primaries of 

 the chick, shows that the region which produces the cells which 

 enter into the formation of the barbules is less in extent than that 

 which enters into the formation of the barbs (PI. XII., Fig. i) ; the 

 barbule producing region representing less than 1.5 mm. of the 

 entire length of these large germs. This region apparently does 

 not begin at the extreme end (inferior umbilicus) of the feather, 

 but slightly above it, and surrounds the wide portion of the 



1 Loc. cit. 



