32 PHYSIOLOGICAL GENETICS 



point to the possibility thai in this case a phenomenon may 

 occur similar to that observed iii the vestigia] case, viz., a second- 

 ary though rather early destruction of already formed eye 

 material. 



A few facts, published recently by Wolsky and Huxley (1936), 

 actually point in this direction, though they are in no way con- 

 clusive as yet. In the Bar eye, there are small areas adjacent 

 anteriorly and sometimes posteriorly to the region of faceted 

 ommatidia in which no facets are found, though the pigment is 

 present. The authors found that in this region the retinula cells 

 and the dioptric apparatus arc lacking and only the pigment- 

 bearing accessory cells are present. This fact may or may not 

 permit conclusions upon the formation of the Bar eye. 



A case of a different type is the development of the eye-color 

 mutant characters of Drosophila. Schultz (1935) has made a 

 special study of the eye pigments of Drosophila. It was known 

 from the work of Johannsen (1924) that the normal Wild eye 

 contains in its pigment cells deep red, orange, and yellow granules. 

 These are contained within the so-called primary and secondary 

 cells and beneath the basal membrane (see Hertweck, 1931). 

 The yellow granules are rather rare and occur only in the primary 

 cells. These pigments appear first about 50 hr. after pupation 

 (25°C), first around the basal membrane, then in the secondary, 

 and last in the primary cells. The general color at this time is 

 tan. At about 80 hr. the color changes to red, again in the same 

 centrifugal seriation, still leaving some yellow granules in the 

 primary cells. 



Both the red and yellow pigments are water soluble and may be 

 separated chemically, and the red pigment can be oxydized into 

 the yellow one. Reciprocally, the tan pigment of the early pupa 

 may be reduced to red by action of H 2 S. This means that only 

 one pigment, in different states of reduction, is present. The 

 eye-color mutants, of which so many have been described, are 

 of two main types. One group shows bright reddish colors. 

 These eyes contain dense yellow or orange pigment in the cells and 

 little pigment below the basal membrane. The second group 

 of more brown shades contains hardly any pigment in the primary 

 cells; red and yellow or only yellow granules in the secondaries. 

 There is also an intermediate pinkish group of the pattern of the 

 first group but with red and yellow granules. Furthermore, in 



