164 DARWINISM AND HUMAN LIFE 



or controlling developmental and metabolic pro- 

 cesses. Injection of extracts of thyroid has usually 

 a beneficial effect in reducing goitre. Injection of 

 extracts of foetus has an effect on the mammary 

 glands. Injection of testicular extract causes the 

 temporary development of a cock's comb on a hen. 

 There are enough of facts of this kind to make us 

 chary of dogmatism in regard to the possibihty of 

 an influence passing from a modification of the 

 body to the germ-cells thereof. As Prof. E. B. 

 Wilson says : " Let us admit freely that such an 

 interaction as Darwin assumed may be a real and 

 potent factor in heredity, though it gives us no 

 hint of its existence in the visible apparatus of 

 the cell. In the present defective state of our 

 knowledge we may well grant that there may 

 be many a thing between germ-cell and body 

 that is not yet dreamed of in our biological 

 philosophy." ' 



A Steiking Case. — Kammerer's experiments on 

 salamanders afford the most remarkable piece of 

 evidence as yet adduced in support of the thesis 

 that acquired characters may be transmitted. 



(a) The common yellow and black-spotted 

 salamander {Salamandra maculosa) is either vivi- 

 parous, producing a large number of larvae 

 25-30 mm. in length with four hmbs and short 

 gills, or ovo-viviparous, lajdng large eggs which 

 hatch out into similar larvae 23-25 mm. in length. 

 After a few months of larval Hfe in the water, 

 they undergo metamorphosis into land-salamanders 

 45-56 mm. in length. 



(6) The black Alpine Salamander {Salamandra 



1 " The Cell in Relation to Heredity and Evolution," in " Fifty 

 Years of Darwinism " (1909), p. 113. 



