SEX-CHARACTERS IN EVOLUTION 123 



the testis affects the development of the antler, as 

 well as our knowledge of hormones in general, 

 suggests a special theory of the heredity of somatic 

 modifications due to external stimuli. Physiologists 

 are apt to look for a particular gland to produce 

 every internal secretion. But the fact that the wall 

 of the intestine produces secretion, which carried by 

 the blood causes the pancreas to secrete, shows that 

 a particular gland is not necessary. There is nothing 

 improbable in supposing that a tissue stimulated to 

 excessive growth by external irritation would give 

 off special substances to the blood. We know that 

 living tissues give off waste products, and that these 

 are not merely pure C0 2 and H 2 0, but complicated 

 compounds. The theory proposed by me in 1908 

 was that we have within the gonads numerous 

 gametocytes whose chromosomes contain factors 

 corresponding to the different parts of the soma, 

 and that these factors or determinants might be 

 stimulated by waste products circulating in the 

 blood and derived from the parts of the soma corre- 

 sponding to them. There is no reason to suppose 

 that an exostosis formed on the frontal bone as a 

 result of repeated mechanical stimulation due to the 

 butting of stags would give off a special hormone 

 which was never formed in the body before, but it 

 would probably in its increased growth give off an 

 increased quantity of intermediate waste products 

 of the same kind as the tissues from which it arose 

 gave off before. These products would act as a 

 hormone on the gametocytes, stimulating the factors 

 which in the next generation would control the 

 development of the frontal bone and adjacent 

 tissues. 



