24 



SCIENCE 



[N. S. Vol. XLVI. No. 1175 



exist in the pigeon's ova have been traced m 

 adults of the two sexes, the parallel rigorously 

 holds there also. A general classification of 

 male and female adult animals on the basis 

 of a higher metabolism for the one, and a 

 lower for the other, was indeed made by 

 Geddes and Thomson^^ many years ago. 

 There can now be little question that this 

 conclusion of these authors is a correct and 

 important one. 



It remains to point out that another very 

 old, and much-worked line of investigation 

 supplies further confirmatory evidence for our 

 present point of view. Studies on the effects 

 of castration, gonad-transplantation, and 

 gonad-extract injection, constitute a large 

 body of observations which deal with sexual 

 phenomena associated with the internal secre- 

 tions of the sex-glands. These internal secre- 

 tions, let it be remembered, are themselves 

 metabolites, which have the capacity to influ- 

 ence the metaholism of some, many, or of all 

 the tissues with which they came 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 ver- 

 tically 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^^ to be mentioned here. 



21 "The Evolution of Sex," 1890, Humboldt 

 Publ'g Co., New York. 



22 The following partial references are suggested 

 by the particular animals listed in the diagram: 

 Sta^— Darwin (1868); Caton (1881); Fowler 

 (1894); Eorig (1900). HMmaji— Hegar (1893); 

 Selheim (1898) ; Hikmet and Renault (1906) ; 0. 

 Wallace (1907); Tandler and Gross (1909). 

 Sheep — Shattook and Seligman (1904) ; Seligman 

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

 pig— Bomn and Ancel (1903-09) ; Steinach 

 (1910-13). P7ieasaret— Gurney (1888). Fowl 

 and Dwfc— Darwin (1868) ; Gurney (1888) ; Foges 

 (1903) ; Shattock and Seligman (1906-07) ; Good- 

 ale (1910-16). Pi^eoTi— Riddle (1914). Frog— 

 Nussbaum (1907) ; Pfliiger (1907) ; Steinach 

 (1910); G. Smith (1912). Inachus and Carcinus 

 —Potts (1909); G. Smith (1910-12). Free-mar- 

 tin — Lillie (1916). Bonellia — Baltzer (1914). 



But the present point of interest is that these 

 results, as a whole, demonstrate that the ex- 

 tent of sexual modification in the experi- 

 mental 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 more 

 profound is the sexual modification of the in- 

 dividual. The stag is a form that has long 

 been known to show thus a considerable and 

 beautiful series. The free-martin — another 

 Ungulate — is now known to exemplify a much 

 earlier point at which the foreign internal 

 secretion begins to act; and here, true to the 

 rule that has been established elsewhere in all 

 this general line of work, the resulting modi- 

 fication is correspondingly strong and striking. 

 When, by whatever means, we effect a change 

 in the metabolism (which is the essential 

 thing) at a still earlier stage — in the egg- 

 stage, in our own and in some other experi- 

 mental reversals of sex, — ^then we obtain 

 individuals whose sexual nature is quite 

 thoroughly reversed ; in many cases completely 

 so, and in still other cases with varying de- 

 grees of completeness. 



Professor Whitman's main decisions con- 

 cerning the nature of sex may here be briefly 

 stated. These decisions were that the male 

 proceeds from a " stronger " germ, has greater 

 " developmental energy," and " carries the 

 processes of development farther " than does 

 the female. I am confident that his results 

 fully justify his conclusions; and that these 

 are in the completest harmony with the later 

 and fuller developments of the sex-studies 

 in the pigeons, and thus with the theory of 

 sex which has been outlined in these pages. 



In conclusion, our present definite knowl- 

 edge of the metabolic basis of sexual differ- 

 ence, and the methods of attack which this 

 new knowledge brings with it, offer the surest 

 guarantees that the problem of sex can now 

 be studied — and, indeed, the basal facts of the 

 problem must be studied — in the field of the 

 elemental protoplasmic functions. 



Oscar Riddle 



Cold Spring Haebor, N. T. 



