_>;>s PHYSIOLOGICAL GENETICS 



category, e.g., the arrangement of hair, feathers, glands, etc., 

 in the skin. 



In studying the wing pattern of Lepidoptera, we had to point 

 out the existence of primarily determined centers (outlets) for 

 the determination process, the centers thus dividing the surface 

 of the organ into fields. The same problem occurs again in the 

 piebald patterns of mammals (also fishes). Goldschmidt 

 (1920/0 pointed out that there the same two phenomena are 

 involved as in the moth wing, viz., the inherited pattern of outlets 

 (field centers) and the control of quantity, berth, time of flow, 

 etc., of the spreading substance responsible for pigmentation. 

 Kuelm (1926) and Henke (1933a) have shown that the fields 

 thus created are rather independent of each other; e.g., A may 

 be black, and B white, or vice versa; in A, very little pigment 

 may have "flown out" from the centers; in B, none; and in C, 

 t he whole field may be covered. This points to a process with a 

 time element, which Goldschmidt (1920c) had termed the order 

 of opening of the outlets. Genetic work with such patterns 

 shows that mutant genes exist, controlling the quantity of released 

 pigment, frequently in an additive way in series of multiple 

 allelomorphs; further, genes controlling the arrangement of the 

 centers and their symmetry; also, genes controlling what we called 

 the order of opening of the outlets, resulting in special features 

 for each field; and, of course, also the genes controlling the color 

 of pigments (see the numerous papers on spotting in mice, 

 rabbits, rats, guinea pigs, horses, dogs, by Castle, Wright, Dunn, 

 Phillips. Ibsen, and others). The material already existing in 

 these groups might profitably be used for a deeper analysis of 

 this type of pattern, an analysis that has not yet been made from 

 the standpoint of physiological genetics. Attention may be 

 called to Iljin's study (1926) of piebald patterns in guinea pigs. 

 He assumes that centers of pigmentation (the outlets) are not 

 found, but centers of depigmentation, i.e., the negative picture. 

 This leaves, however, the problem of gene-controlled pattern 

 where it was. The facts reported above (page 155) regarding 

 Himalayan rabbits and Siamese cats, demonstrating an interest- 

 ing interaction between gene products and environment, ought 

 also to be kept in mind, because internal conditions might assume 

 the role of environment and superimpose a pattern effect upon 

 a nonpatterned gene effect. 



