188 PHYSIOLOGICAL GENETICS 



that this points to a difference in distribution of some regulatory 

 substance, possibly a growth hormone. There is also a third 

 gene n which probably nets upon the production of the same stuff. 



In this chapter, we ought to mention also those cases where 

 actual and known hormones are controlled by genie action. 

 [We have discussed (page 77) the facts of inheritance of the 

 number of molts in insects, controlled by a series of allelomorphic 

 genes. In these cases, however, we need not assume that the 

 genes in question lead to a production of hormones but only that 

 they are connected with the time of release of a hormone. 

 For this reason, the case was reported in the chapter on rates.] 



There is, for example, the case of the dwarf gene in mice as 

 analyzed by Smith and McDowell (1930). It was shown that 

 this gene works by controlling the production of a growth hor- 

 mone in the pituitary gland, the insufficiency of which leads to 

 dwarfism and other abnormalities. Another probably more 

 complicated case taken from the sphere of sex hormones is the 

 much discussed case of the hen-feathered Bantam cocks. Hen- 

 feathering is controlled by a dominant gene (perhaps two), as 

 found by Morgan (1919) and Punnett and Bailey (1921). 

 Castrated cocks become normally cock-feathered, and trans- 

 plantation of any testis produces a return to hen-feathering. In 

 normal fowl, the male type of plumage is the genetic type, and 

 the female type is caused by the female sex hormone. According 

 to Callow and Parkes (quoted from Haldane, 1935), the Bantam 

 feathers respond with female type to a very low concentration of 

 female hormone. As there is some female hormone also in normal 

 testis secretion, the gene responsible for hen-feathering produces 

 a low threshold of response to the female hormone. If these 

 results are as significant as they appear, the gene in question 

 actually does not control the production of the hormone, but a 

 condition in the feather follicles, setting a threshold to hormone 

 action. 



It will probably be found that the production of hormone-like 

 substances, i.e., diffusion and vascular hormones, plays a much 

 more important part in development than is known at present. 

 We expect that such processes will be found wherever an organ 

 differentiates in some respects as a unit. We know already some 

 cases from which such a situation may be inferred. There 

 is the case of the insect gonad, as analyzed in the intersexuality 



