602 
GEOPi'REY SMITH. 
nervous communication, or else by means of substances con- 
veyed in the blood or body-fluids. The former supposition is 
ruled out by a number of experiments, such as the severance 
of the nerves to the reproductive organs, etc., so that we are 
perforce thrown back on the second supposition of internal 
seci’etious, although the participation of the nervous system 
is not altogether precluded. 
It would also seem probable that sexual difi^erentiation does 
not solely depend on the presence and nature of these sub- 
stances, but rather in the interaction of these substances 
with the cells of the organism, which may themselves be 
differentiated beforehand in the two sexes. The attempt to 
analyse the nature of the sexual formative substance and its 
relation to the primary and secondary characters will occupy 
us in succeeding parts. 
Literature. 
1. Bateson, W. — Mendel’s ‘ Principles of Heredity,’ 1909. 
2. Castle, W. — “ The Heredity of Sex,” ‘ Bull. Mus. Comp. Zool. 
Harvard,’ vol. xi, 1903. 
3 . McClung, C. — “ The Accessory Chroniosoine — Sex Determinant ? ” 
‘ Biol. Bull.,’ iii, 1902, p. 43. 
4. Wilson, E. B. — “ Studies on Chromosomes,” ‘ Journ. Exp. Zool.,’ 
vols. ii and iii, 1906 and 1907, and other papers. 
5. Smith, G. — ‘ Fauna and Flora des Golfes von Neapel,’ Monogr. 29, 
1906. 
6. Bateson, W., and Punnett, R. — “ The Heredity of Sex,” ‘ Science,' 
N.S., xxvii, 1908, p. 785. 
7 . Doncaster, L. — “ Sex Inheritance in the moth, Abraxas grossu- 
lariata,” ‘Rep. Evol. Comm.,’ iv, 1908. 
8. Correns, C. — ‘Die Bestiniung und Vererbung des Geschlechtes,’ 
Berlin, 1907. 
9. Heape, W. — “Note on the Proportion of the Sexes in Dogs,” ‘Proc. 
Camb. Phil. Soc.,’ vol. xiv, 1907, and ‘ Phil. Trans. Roy. Soc. 
London,’ vol. cc, 1908, p. 271. 
10. Punnett, R. — “Sex Determination in Hydatina,” ‘Proc. Roy. 
Soc. London,’ vol. Ixxviii, 1906, p. 223. 
