THE MUTATED GENE 185 



in the testis or ovary or brain by the action of the gene .1 is 

 actually a hormone. Whether this hormone acts also within the 

 cells in which it is found has not yet been decided. 



To these facts have been added recently a number of quantita- 

 tive data by Kuehn and Plagge (1936). The presence of an 

 A -testis in an a-pupa for only 24 hr. suffices to produce the effect. 

 One grafted ovary produces less of the hormone than one testis 

 in 24 hr. ; two ovaries produce more. A single egg tube, which 

 is dissolved after transplantation, produces more hormone than 

 a whole intact ovary, viz., about the same amount as a day's 

 production of a testis. (This is proved to be actually boun<$ to 

 the presence of the .4-gene.) A dissolved testis, however, does 

 not produce the hormone. It seems therefore that the testis 

 produces, and the ovary stores, the hormone. The same hor- 

 mone occurs in many other species of Lepidoptera, as trans- 

 planted testes from many different species produce the A -effect. 



Another method, invented by Beadle and Ephrussi (1935- 

 1937), has led to results that fall in line with those already 

 mentioned. (Part of their work has already been mentioned 

 on page 166.) They transplant in Drosophila the imaginal disks 

 of eyes of different genetic constitutions into the body of larvae 

 of definite constitution and recover the transplant after it has 

 finished development in the host. Three types of result are 

 possible. Either the transplant is not influenced by the host; 

 i.e., its development is autonomous; or the transplant assumes 

 the color of the host. In the latter case, the host must produce 

 a hormone-like substance, acting upon the transplant. As a 

 third alternative, the transplant may be intermediate in color, 

 which would amount to an insufficient hormonic action of the 

 host. The diagram (Fig. 34) shows the authors' results with a 

 large number of eye-color mutants. The majority of eye colors 

 show autonomous development. But vermilion and cinnabar 

 are exceptions; they are influenced by the host. Vermilion 

 implanted into Wild type or into all the color mutants marked 

 on top of the diagram gives Wild-type eyes with a few exceptions: 

 it gives vermilion in claret (ca), carmine (en), peach (p p ), and 

 ruby (rb) and an intermediate condition in carnation (car) and 

 garnet (g 2 ) hosts. Parallel are the results with cinnabar, as 

 may be read from the diagram. A Wild-type disk transplanted 

 into mutants always gives Wild-type pigmentation with the 



