272 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



time when the recipient tissue has already lost its ability to interact with this 

 hormone. Thus the anterior pituitary may continue to produce follicle-stimu- 

 lating hormone in old persons, at a time when the ovary no longer possesses 

 the structures which are able to react with this hormone. In a comparable 

 manner, according to Mangold, the epidermis of axolotls is unable to respond 

 with the production of a balancer at a time when the adequate organizer is 

 present in the archenteron and medullary plate; but in other urodeles the 

 recipient organ may actively respond to the presence of this organizer. 



In recent years it has been discovered that there are hormones which medi- 

 ate some effects of genes on those tissues which are under the control of these 

 genes (Kiihn, Ephrussi, Beadle). Such hormones develop, therefore, not 

 under the influence of cytoplasmic, but of nuclear constituents. They may 

 transmit to distant places, for instance, the effects of genes which distinguish 

 the dominant characteristic of a wild race from the recessive characteristics 

 of a mutant race. These gene-hormones have been found in various orders 

 of insects, such as Ephestia, Bombyx, Habrobracon and Drosophila ; they may 

 occur in certain organs (ovary, testis, brain), or in the body fluids, and they 

 can be conveyed to other organisms either by implantation of these organs 

 or by injections of the bodyfluids. If the hormone is transmitted in this manner 

 to a mutant individual which lacks the gene that causes the development of 

 a certain eye pigment, it acquires now the ability to produce the eye color of 

 the dominant race. Such genes thus seem to exert their effects on the recipient 

 tissues by means of hormone-like substances to which certain tissues have a 

 specific affinity. These gene-hormones are not species-specific; they may be 

 effective even in different orders of animals. Ephestia as well as Habrobracon 

 hormones are effective in Drosophila, and conversely, Drosophila hormones 

 exert typical effects in Habrobracon pupae. It is, in all these cases, the wild 

 dark-eyed type which possesses a hormone which is lacking in the mutant 

 form. As to the chemical constitution of such hormones, they seem to be 

 neither protein nor lipoid; they, as well as the organizers, apparently lack 

 organismal differentials. 



We see, then, that the organizers, on which the organ formation in the 

 embryo depends to a large extent, and the substances, by means of which the 

 genes produce their effects during embryonal or larval life, are both hormone- 

 like and do not possess the organismal differentials; whereas the substances 

 from which they are derived, the cytoplasm of embryonal tissues and organs 

 and the genes of the chromosomes, have a complex structure and do possess 

 organismal differentials or their precursors. Likewise, the substratum on 

 which they act are bearers of organismal differentials or their precursors. 

 The cytoplasm is the more specific material which has the potentiality to 

 develop and differentiate within certain limits under the influence of these 

 hormone-like inductor substances. The latter induce the development of organ 

 systems in an orderly fashion, in accordance with the organismal differentials 

 of the species and the individual in which they act. Both the precursors of the 

 organizers and the organismal differentials are presumably present in the 

 fertilized ovum. In the course of embryonal life the organ precursors and the 



