84 REPORTS ON INVESTIGATIONS AND PROJECTS. 



ably, be initiated by the hybridization of the two forms with an unequal 

 number of chromosomes. 



PIGMENTATION. 



Of all the morphological characters of organisms the pigment is one of 

 the simplest and its manufacture would, it is to be expected, lend itself most 

 readily to modification by chemical and other means. Thus it is known that 

 sunlight influences (even in the human skin) the formation of pigments, 

 and that animals removed from the influence of sunlight, such as those that 

 live in caves, in grottoes, or within opaque shells, develop little or no pig- 

 ment. It has often been gratuitously assumed that they had lost the power 

 of manufacturing materials for pigment, but experiment shows that this is 

 not always so, for, subjected to sunlight, pigment appears. It was hoped 

 that in our artificial cave pigment-production would be inhibited in some 

 animals as in the caves, and this proves to be the case. The salamander 

 (Amblystoma) larvae that have hatched in the cave and are now a year and 

 a half old are still "white" — they have no more pigment than many cave 

 species of long standing. Nevertheless, pigment production is not wholly 

 inhibited. The mud minnows (Umbra limi) which have been kept in the 

 cave for nearly 2 years are showing a progressive reduction in amount of 

 pigment. Other material in the artificial cave gives promise of especially 

 interesting results. These studies have been made by Dr. Banta. 



In our studies on the inheritance of plumage color in poultry it early de- 

 veloped that there are two kinds of whites, namely, whites which when 

 mated with pigmented birds give pigmented offspring, and whites which 

 when mated with pigmented birds give only unpigmented offspring. Indeed, 

 these two kinds of whites, recessive and dominant, are now recognized as 

 widespread in nature. The white of sheep's wool is another dominant dis- 

 covered by us. According to modern methods of interpretation, recessive 

 whites are those whose lack of pigment is due to an absence of one or more 

 of the factors necessary to pigment production. And dominant whites are 

 to be explained on the assumption of some additional factor. What that 

 additional factor might be has been unknown, and Dr. Gortner has been 

 seeking for it. Now black pigment, "melanin," is produced by the oxidation 

 of tyrosin in the presence of an oxidizing ferment, tyrosinase. It was sug- 

 gested by Spiegler, before Dr. Gortner began his work, that the dominant 

 white was due to a superoxidation of the melanin. If this conclusion were 

 correct it should be possible to isolate the melanin — only it should be white. 

 Dr. Gortner soon showed that Spiegler's conclusion was wrong. The "white 

 melanin" from sheep's wool is only the insoluble portion of the keratin and 

 is not pigment at all. It seemed probable, consequently, that the dominant 

 factor in white wool is an inhibiting factor, which prevents the pigment- 

 forming elements, though present, from combining. This explanation re- 

 mained pure hypothesis until tested, and this test Dr. Gortner, working with 



