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stimulating effect of the hormone produced by the male organ in 

 each species, they afford at least one good instance of the produc- 

 tion of a specific change of form as the result of an internal chemical 

 stimulus. We get here a hint as to the nature of the chemical 

 mechanism which excites and correlates form and function in higher 

 organisms, and from what has just been said, we perceive that this 

 is the most primitive of all the animal mechanisms. I submit that 

 this is a step towards forming a clear and concrete idea of the 

 inner nature of the organism. There is one point and that a very 

 important one, upon which we are by no means clear. We do 

 not know how far the hormones themselves are liable to change, 

 whether by the action of external conditions or by the reciprocal 

 action of the activities of the organs to which they are related. 

 It is at least conceivable that agencies which produce chemical 

 disturbances in the circulating fluids may alter the chemical con- 

 stitution of the hormones, and thus produce far-reaching effects. 

 The pathology of the thyroid gland gives some ground for belief 

 that such changes may be produced by the action of external 

 conditions. But however this may be, the line of reasoning that 

 we have followed raises the expectation that a chemical bond must 

 exist between the functionally active organs of the body and the 

 germ-cells. For if, in the absence of a specialised nervous 

 system, the only possible regulating and coadapting mechanism is 

 a chemical mechanism, and if the specific activities ot a cell are 

 dependent on the enzymes which it holds in combination, the 

 germ-cells of any given animal must be the depository of a stock 

 of enzymes sufficient to insure the due succession of all its deve- 

 lopmental stages as well as of its adult structure and functions. And 

 as the number of blastomeres increases, and the need for coordi- 

 nation of form and function arises, before ever the rudiments of 

 a nervous system are differentiated, it is necessary to assume that 

 there is also a stock of appropriate hormones to supply the che- 

 mical nexus between the different parts of the embryo. The only 

 alternative is to suppose that they are synthesised as required in 



the course of development 



It would seem, therefore, that there is some theoretical justifica- 

 tion for the inheritance of induced modifications, provided that 

 these are of such a kind as to react chemically on the enzymes 

 contained in the germ-cells. " 



