1008 BR. E. A. WILSON ON TUB [June 14, 



the Hanks of hen Grouse which show every possible graduation 

 between the perfect winter-pkunage, ahiiost vermiculate, flank- 

 feather and tlie broad-barred, breeding-season, flank-feather of 

 the summer hen. But it is very much more probable that the 

 growing period of these ambiguous or intermediate feathers is 

 one of great susceptibility to outside conditions, as we know 

 the case to be in respect of the metal)olic processes which are 

 taking place witliin the hen-bird at the time. These are known 

 to be exceedingly sensitive. Pigment is indispufcibly a product 

 of tissue metabolism. It is often proba])ly a mere waste product, 

 but it appears at times to serve a special function notwithstanding. 

 It is also certain that pigment is a production whose appearance, 

 or failure to appear, is open to considerable vicissitudes in 

 Consequence of small recognized changes in physiological condition, 

 and many le.ss easily recognized changes in the general metabolism 

 of the body. 



In the hen Grouse during the breeding- season pigment 

 production is very actively at work, for we know that a very 

 lai-ge amount is being produced for excretion in the pigment- 

 glands of the lower part of the oviduct. This pigment, moreover, 

 is precisely of the shade and colour which is characteristic not of 

 the breeding- plumage, but of the winter dress of the hen and the 

 cock Red Grouse. It is deposited in abundance normally on every 

 egg, but it may also abnormally fail to be deposited or even 

 produced at all, not only for the eggs in the oviduct, but in the 

 circulating blood of the bird's whole system. Thus the feathers 

 instead of becoming bufi" or brown, i-eddish or even black as they 

 proceed in growth, may be any intermediate paler shade of butt', 

 or even white, a character which is due generally to the complete 

 absence of all pigment granules. The place of the pigment 

 in such feathers is probably taken by shining air-globules, as 

 it is in the hair and feathers of the majority of white animals and 

 birds. 



It is theiefore easier to believe the suggestion that a sudden 

 check, either by a change of temperature, or by wet and cold, or 

 by want of sunshine, or l)y change in food, has for the time being 

 so far afl'ected the tissue metiibolism of the bird that n feather 

 which began to grow ujion a circuliition lacking pigment particles, 

 or the waste products which produce them, and which was 

 therefore originally planned for the paler plumage, may, by a 

 sudden increase in the metabolism of the bird and so in the out- 

 pvit of waste products to the blood, be completed as a feather of 

 the more deeply pigmenteil jilumnge, thus producing a feather 

 witli the characters of l)oth. 



This is a phiusible explanation, l)ut is still open to some doubt, 

 for the difference l)etween the broad-banded buff and black flank- 

 feather of the nesting hen, and the dark red-brown finely cross- 

 linetl featlier of tlie same bird in winter, is olniously greater as 

 regards ])igiiu'nt distril)uti()ii than as regards the actual tiuantity 

 of pigment deposited in the feathers. 



