XXV.—An Histological Analysis of Eye Pigment Development inDrosophila pseudo-obscura

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Abstract
It is generally accepted that the function of the mutant genes which affect eye colour in Drosophila is to produce either quantitative or qualitative changes in the normal development of eye pigment. Wright (1932) believes that these genes act by interfering with some part of a chain of reactions which give rise to eye-colour characteristic of the wild type. Mainx (1935) suggested that recessive eye-colour genes (with the exception of sepia) reduce the total amount of pigment, and that the degree of reduction is characteristic for each gene. Transplantation experiments of Beadle and Ephrussi (1935, 1936, 1937 a and b) have led them to the view that certain eye-colour mutants lack specific substances which are necessary for the development of additional pigment present in wild type eye colour. Johannson (1924) and Schultz (1935) studied the histology of the adult eye of D. melanogaster and classified the mutant eye colours according to the distribution of granules in their pigment cells. Schultz (1932) had previously noted the time of pigment deposition and subsequent changes in wild type and some mutants of D. melanogaster. In an earlier paper the author (1936) described in detail similar colour changes in the eyes of developing pupæ of D. pseudo-obscura. Previous work in this laboratory (1932, 1934, 1935) by Crew and Lamy make it appear that each mutant eye colour is the expression of a gene which acts to suppress normal development during a certain period of time, allowing the rest of the development to proceed as in wild type.