No. 508] NOTES AND LITERATURE 



•219 



In 1876 Darwin had become a true eeologist. In this year he wrote 

 to Professor Moritz Wagner as follows : " The greatest mistake I made 

 was, I now think, I did not attach sufficient weight to the direct 

 influence of food, climate, etc., quite independently of natural selection. 

 When I wrote my book and for some years later, I could not find a good 

 proof of the direct action [t. e., in producing definite variations] of 

 the environment on the species. Such proofs are now plentiful [Hens- 

 low says 'universal']." 



Plant ecologists . . . are accepting " Adaptation " by response as a 

 proved fact. ... A complete change of front has taken place within 

 the last twenty years, but as Darwin himself was the first [?] to pro- 

 pound this view, I called it " The True Darwinism." 



Zoologists have been rather behind the botanists in ecological 

 work, but the zoological school of ecology is growing and it does 

 seem true that the more organisms are studied with regard to 

 their relations to their environment, "at home," the stronger 

 becomes the belief in the importance of environment in evolution. 

 Whether this is "True Darwinism" or something else is im- 

 material, only so it be true. 



The most serious difficulty has been to get a good way of 

 accounting for the inheritance of characters produced by the 

 environment. Cunningham 2 seems now convinced that this 

 difficulty is removed by "hormones," or internal secretions, 

 retracting his former idea that the nexus between secondary 

 sexual characters and the gonads is nervous. Starling's proof 

 that the growth of mammary glands in an unimpregnated rabbit ' 

 is caused by injection of extracts of foetuses from pregnant rab- 

 bits is given as an illustration of the working of hormones. Ap- 

 plied to the development in phylogeny of horns, for example, it 

 is supposed to work about as follows : 



Since the development of the somatic sex-characters is due to the 

 stimulation of the cells by a hormone derived from the gonad, it is 

 conceivable that the gametes may be affected by the internal secretion 

 of the somatic cells whose development constitutes the sex-dmnwter. 

 It is quite possible that the hormone in the case of the gonad, per- 

 haps in all cases, is merely the waste product of metabolism occurring 

 in the cell-multiplication. Whether this is so or not, the somatic 

 Mnu-nm.. such as the antler, would naturally excrete into the blood 

 special substances, and these being in the blood the gametes would be 

 multiplied and developed under their influence. We can not suppose 

 that all cells or parts of the body produce living ge 

 collected in the germ-cells, but we have reason to 

 -'The Heredity of Secondary Sexual Characte 

 Hormones, a Theory of the Heredity of Somatogenic CI 

 Entwicklungsmcchanil; XXVI, 3, 1908. 



conclude that 



