182 PHYSIOLOGICAL GENETICS 



produced by the action of genes: hormones of the first order — 

 intracellular formative or inductive substances; hormones of 

 the second order inductors diffusing from their place of origin 

 and thus acting at a distance (identical with the harmozones of 

 Gley); hormones of the third order, or hormones proper — 

 carried by the body fluids. Meanwhile, the work of the embry- 

 ologists has centered considerably around the second type of 

 inductors; and it is necessary to use a definite terminology for 

 the possible morphogenetic stuffs. That the term hormone was 

 extended beyond its original meaning to cover all the types of 

 stuffs has been much criticized. I still think that the general 

 idea underlying this generalization is correct; but this does not 

 prevent the use of any terminology that appears better founded. 



In a recent paper, Huxley (1935a) proposed a clarification of 

 the terminology. He points out that all transitions are found 

 between the types of morphogenetic substances mentioned; 

 e.g., the activating substance studied by Haemmerling in the 

 unicellular plant Acetabularia is, of course, intracellular, but it 

 is shown to act by diffusion from the nucleus to the mushroom- 

 like periphery of the complicated cell. Similar examples are cited 

 that bridge the difference between diffusion hormones and vas- 

 cular hormones. He proposes, therefore, to call all these sub- 

 stances activators. They may be local activators acting on the 

 cell or tissue that produces them. These again are subdivided 

 into intracellular activators and chemodifferentiators, the latter 

 containing all the activators for predetermination of embryonic 

 parts. (These may also show transitions to a type with diffu- 

 sion.) The second main group is distance activators, or hormones. 

 They are transported either by diffusion — diffusion hormones — 

 or by the body fluids — circulatory hormones. This system is, 

 after all, very much like that used by Goldschmidt. We shall 

 then use the word activator in a general sense, replacing it occa- 

 sionally by inductor or evocator when the embryological processes 

 of a general type are involved ; and we shall use the word hormone 

 mostly for distance action only. 



2. Genie Products of the Hormone Type. — A few facts are 

 known that might be reported as a transitional step between 

 the cases with a spread of a gene-controlled effect from cell to 

 cell and a corresponding effect at a longer distance. Bonnier 

 (1928) described a Drosophila mosaic in which a Bar eye on one 



