THE MUTATED GENE 



173 



There is another case that has also been frequently discussed 

 in Goldschmidt's writings — the abnormality called prothetely. 

 In these cases, which at least sometimes are caused genetically, a 

 single organ or a few organs are ahead in development. Most 

 typical are the cases in insects, where a caterpillar forms pupal 

 antennae (see Goldschmidt, 19236) or pupal wings (Tenebrio, 

 Ferwerda, 1928) (Fig. 33). As it is known now that the evagina- 

 tion of the imaginal disks is under hormonic control, this means 

 probably that in these cases the threshold has been lowered 

 locally. In any case, there is some dis- 

 turbance of reactions that are normally 

 definitely tuned and that have to do 

 with hormonic control of developmental 

 processes. 



There can be no doubt, then, that the 

 combined action of the genes in control- 

 ling developmental processes occurs in 

 the form of a system of gene-controlled 

 reactions, which have to be in proper 

 tune to work together harmoniously. A 

 definite stuff, a definite physical or chem- 

 ical property of the cytoplasmic sub- 

 stratum, must be present at a definite 

 time and place to make the proper course 

 of other reactions possible. This inter- L 

 play of reactions in tune is the physio- , FlG - 33 \7 Case .,, of , p T ro ~ 



*" f i • i • i thetely. Caterpillar of Ly- 



logical process, which is meant (or OUght mantria dispar with pupal 



to be) when one speaks of genie balance an tennae. (From Goid- 



. . schmidt.) 



or of all the genes taking part in all 



determinations. There is much loose thinking in this field. 

 One has, for example, argued as follows: There are so 

 and so many genes known to influence the eye color in 

 Drosophila. Therefore so many times more genes must be 

 involved in the determination of an eye, and so many more for 

 the whole normal development. The proper argumentation 

 would be: Numerous reactions are involved in orderly develop- 

 ment, including also the development of the eye and its details. 

 As the formation of eye pigment in definite cells is a chemical 

 process which is dependent upon a number of chemical and 

 morphogenetic situations, which in their turn are dependent upon 



