33O OSCAR RIDDLE. 



what is actually produced is, in several demonstrated instances, 

 dependent upon the physiological state of the organism. Or, per- 

 haps, in certain cases it may be possible to say more definitely 

 that the limiting factor is none other than the available oxygen 

 or food-supply. I have been able to prove ('oS) definitely that 

 in many birds the daily nutritive changes which accompany the 

 low blood-pressures occurring at night influence the quantity of 

 melanin produced. 



The specific color of an animal then is an index, not of the 

 presence in the germ from which this animal arose, of certain 

 chromogens and specific zymogens, and the absence of a wide 

 series of others ; but, this specific color means that a process with 

 a wide range of possibilities, because of a particular physiological 

 state and environmental conditions has struck this particular equi- 

 librium. One and the same organism has within it all tJiat is 

 necessary to move that equilibrium up or down-- taking the red 

 form for example, we can in the words of Tornier " force it to 

 black or to white." 



Tornier did not consider the relation of his results to any of 

 the facts of the chemistry of melanin, nor did he consider their 

 bearing on color inheritance. His chief concern has been appar- 

 ently to establish two points in color physiology ; first, the effect 

 of varying degrees of nutrition on the size, shape, color-produc- 

 tion, etc., of chromatophores ; and, secondly, a defense of the 

 thesis that the pigment granules of these chromatophores act as 

 reserve food-materials in cases of inanition, etc. 



MENDELIAN DESCRIPTION. 



It is now possible to consider whether Mendelian interpreta- 

 tion and description is in accord with the facts of color formation. 

 The Mendelian position can be best presented in the words which 

 Cuenot ('03) used in the original formulation and statement of 

 it. I quote practically the whole of his discussion, and ask that 

 it be remembered that it is almost entirely upon this slender basis 

 that the "presence, absence" hypothesis, and consequently a 

 great share of Mendelian nomenclature, rests : 



" Again one learns that the authors whp have recently studied 

 the origin of melanin pigments, Biedermann, v. Furth, Schneider 



