352 riddle: control of sex ratio 



come in contact or which they may reach indirectly." A par- 

 tial list of the animal forms that have been most studied in this 

 respect is written serially on the top of our diagram — in a 

 position intermediate to egg and adult. The number of these 

 animal forms might be much increased, and the names of the 

 investigators of this aspect of the modification of sex are quite 

 too numerous 12 to be mentioned here. But the present point 

 of interest is that these results, as a whole, demonstrate that 

 the extent of sexual modification in the experimental animal is, in 

 general, in proportion to the immaturity of the treated animal. 

 That is to say, the earlier the internal secretion of the gonad is 

 supplied or withdrawn — the earlier the metabolic change is 

 effected — the more profound is the sexual modification of the in- 

 dividual. All this is of course clearly in conformity with the 

 Law of Genetic Restriction — a principle of embryology that is 

 true alike for all of the known characteristics of the organism. 

 Of the several animals of the list we may here particularize 

 concerning only two or three. The stag is a form that has long 

 been known to show thus a considerable and beautiful series of 

 greater modification of antlers and other so-called secondary 

 sexual characters, in correspondence with castration at earlier 

 and earlier periods in the life of the animal. The free-martin 

 — another Ungulate — is now known to exemplify a much ear- 

 lier point at which the foreign internal secretion begins to act; 



11 That changes following the removal of gonads, etc., have for many years 

 been recognized as connected with a changed metabolism may be illustrated 

 from the following quotation from Marshall ('10). "The effects of castration 

 indicate that an alteration in the metabolism, even in comparatively late life, 

 may initiate changes in the direction of the opposite sex" (p. 658). 



12 The following partial references are suggested by the particular animals 

 listed in the diagram: Stag, Darwin (1868); Caton (1S81); Fowler (1894); 

 Rorig (1900). Human, Hegar (1893); Selheim (1898); Hikmet and Renault 

 (1906); C. Wallace (1907); Tandler and Gross (1909). Sheep, Shattock and 

 Seligman (1904); Seligman (1906); Marshall and Hammond (1914). Guinea- 

 pig, Bouin and Ancel (1903-9); Steinach (1910-13). Pheasant, Gurney (1888). 

 Fowl and Duck, Darwin (1868); Gurney (1888); Foges (1903); Shattock and 

 Seligman (1906-7); Goodale (1910-16). Pigeon, Riddle (1914 a). Frog, Nuss- 

 baum (1907); Pfluger (1907); Steinach (1910); G. Smith (1912). Inachus and 

 Carcinus, Potts (1909); G. Smith (1910-12). Free-martin, Lillie (1916). Bo- 

 mllia, Baltzer (1914). 



