Cunningham's Position 175 



in the nature of the parental modification. The chain 

 would be like this: (1) An extrinsic change in sur- 

 roundings, food, or habits; (2) a dint or imprint on 

 a particular structure in the organism; (3) the lib- 

 eration of specific products (of the nature of hor- 

 mones), due to the modification in question, and their 

 transport to the germ-cells; (4) a representative 

 resultant in the offspring, due to the specific influence 

 of the hormones on the relevant "factors" in the 

 germ-cells. This theory, which obviously deserves 

 careful consideration, has been made available in 

 elaborated form in Mr. Cunningham's Heredity and 

 Hormones (1921). 



What distinguishes Mr. Cunningham's suggestion 

 from Darwin's "provisional hypothesis of pangene- 

 sis" is that, while we know nothing about gemmules, 

 we know a little about hormones. They are "chemical 

 messengers," stirrers-up and soothers-down, pro- 

 duced in ductless glands and tissues of internal secre- 

 tion. They are liberated into the blood, where they 

 circulate like keys seeking the particular locks which 

 they fit. Gemmules are hypothetical, but hormones 

 are real, and the potency of those formed by such 

 structures as the thyroid gland, the supra-renal cap- 

 sule, the pituitary body, and the gonads is well known. 

 It has been proved up to the hilt that the influence of 

 the hormones from the male reproductive organs in 

 birds and mammals is necessary for the actualizing 

 of masculine characters like decorative plumage, 

 wattles, spurs, and antlers. Similarly, the influence 

 of the hormones from the ovary tells on the develop- 



