406 Action of the Genetic Material 



Lymantria dispar there are races that have four molts in both sexes, 

 others with lour in the male and five in the female, and others with 

 five in both sexes. In Lymantria we know (Goldschmidt, 1933a) that 

 the genie control of growth as such is based upon multiple factor 

 inheritance and different setups in different races. The genetics of the 

 molting races has been worked out for the silkworm by Ogura ( 1931 ) . 

 The details are not very simple, but Ogura accounts for them by a 

 series of multiple alleles plus modifier systems. In Lynuintria I could 

 account for the facts satisfactorily by a series of three alleles: Ti 

 produces four molts in both sexes; T2, four in the male, five in the 

 female; and T3, five in both sexes. (We might have mentioned this 

 case when discussing dosage compensation. Here is another example 

 of a situation in which the same autosomal mutant acts differently in 

 the developmental systems of the two sexes.) The different develop- 

 mental systems may be illustrated by the different details of the growth 

 curves. In this genetic system we are dealing clearly with the same 

 type discussed before, involving kinetics of genie action, threshold 

 conditions, and so on; this is demonstrated by the fact that (in the 

 silkworm) variation into the next higher or lower type exists, and 

 that the number of molts can be modified by temperature action 

 (Ogura, 1931; Kiihn and Piepho, 1936) or by hunger (Goldschmidt, 

 1933a). 



In this case we know that the direct cause of the molts is found 

 in the hormonic system, and therefore its functioning is under genie 

 control. The number of molts is, of course, determined by the occur- 

 rence of the last, the metamorphosing molt. This again is the result 

 either of stoppage of the function of the corpora allata or of decrease 

 of their hormonic production with increase of that of the thoracic 

 gland. The role of the mutant loci controlling the number of molts 

 thus can have any of the following functions : ( 1 ) to time the ending 

 of corpus allatum secretion; (2) to control the total amount of juvenile 

 hormone which can be synthesized; (3) to control the threshold condi- 

 tions for the thoracic gland hormone concentration which overtakes 

 that of the other hormone, a function which may be related to relative 

 speeds of two genically controlled processes. ( Wigglesworth has 

 pointed out the similarity of such an action to the one at work in 

 the control of intersexuality in Lymantria by two competing reactions 

 of different speed. ) Whether one of these possibilities, or still another, 

 obtains, certainly the genically controlled reactions are not simply 

 the hormone-producing ones but reactions interlinked with others 



