404 Action of the Genetic Material 



seems, revealed differences only in the genetic sex determiners; genet- 

 ically controlled differences in hormonic action have not been ana- 

 lyzed, though they can be inferred from the work of Gallien (1954). 

 He showed the existence of a series of different responses to the sex- 

 inverting effect of female and male hormones upon larvae of frogs and 

 newts, according to the species used. In some species, male hormones 

 acted positively, but not the female hormones; in others, no complete 

 sex reversal occurred, but only intersexuality resulted, and so on. 

 Comparable facts are available for sex hormones of birds, as discussed 

 in my book of 1931 and numerous reviews on sex and hormones (e.g., 

 Witschi, 1950). 



The best material available deals with insects since Wiggles- 

 worth's ( 1934 ) famous discovery of hormonic glands and their action, 

 and especially with larval molting. Insects grow by molting (the 

 instars) and the number of molts is genetically determined. The last 

 molt in holo- and hemimetabolic insects is the metamorphosis molt. 

 This molting system is under the control of two types of hormones. 

 First is the hormone secreted by the corpus allatum, the juvenile 

 hormone. In its presence a larval molt occurs. After the last larval molt 

 the corpus allatum ceases to function, and the second hormone, 

 produced by the prothoracic gland, takes over ( as it does after removal 

 of the corporata allata), and metamorphosis results. Whether this is 

 the result of absence of the juvenile hormone or only of a superior 

 quantity of the metamorphosis hormone is a special question. There 

 are many detailed facts on the interaction of these hormones (see 

 Wigglesworth, 1952; Bodenstein, 1953fo ) which do not concern us here. 

 However, it should be added that both, number of molts and type of 

 molt, can be influenced and completely changed by external agencies. 

 Temperature action or asphyxiation may induce precocious total or 

 partial metamorphosis; other temperatures and hunger may change 

 the number of molts (literature and details in Goldschmidt, 1938a; 

 and Wigglesworth, 1952). Whether this is an effect upon the hor- 

 mones, or upon the gland, or upon the substrate of hormonic action is 

 not known. However, there is certainly an element of timing con- 

 tained in the relation of the two types of hormonic action which has 

 something to do with the independently determined growth processes, 

 perhaps through some threshold conditions. 



The next important point for this hormonic action is, just as for 

 the parallel direct genie actions, the condition of the substrate, the 

 larval epidermis, or its competence. There is no reason why this com- 

 petence should behave identically in different forms. If, for example 



