THE MUTATED GENE 



39 



B. Mutant Character and Developmental Stage 



In the case of the Gammarus eye, we have encountered the fact 

 that the adult mutant type shows a condition that may also be 

 described as the fixation of a definite developmental stage This 

 is clearly an important point for an understanding of the action 

 of the gene, as was emphasized by Goldschmidt in the first stages 

 of his work on interscxuality (19176, 1920c) and therefore some 

 more facts ought to be mentioned at this point of the analysis. 



Fig. 15. — a, male genital armature of Lymantria dispar. Pe penis, Ps sheath 

 of penis, Ri segmental ring, Sa Saccus, U uncus, Va valva; b, the same in low 

 intersexuality, also after temperature treatment; uncus double. {From Gold- 

 schmidt, 1920.) 



A very frequent type of abnormality is the Hemmungsmiss- 

 bildung. This means that development has simply stopped at a 

 definite stage with the result that an embryonic condition is 

 carried into the adult stage, with such modifications, of course, as 

 are impressed upon the organ by the further development of the 

 whole. These abnormalities very frequently involve incomplete 

 concrescence of embryonic parts, like harelip, hypospadia, cleft 

 eye, and cleft palate. Many such types are also caused by 



