THE DETERMINATION OF SEX. 35 



SUMMARY. 



I. The epoch at which the sex is finally determined is variable in different 

 -animals, and diverse factors operate at successive epochs. 



II. Theological and metaphysical theories of sex have preceded the.scientific ; 

 observation and statistics have been resorted to before experiment ; and over 

 500 theories in all have been set forth. 



III-VI. That there are two kinds of ova is still for the most part an assumption ; 

 that the entrance of more than one spermatozoon normally occurs, and is a 

 determining factor, is erroneous. Thury's emphasis on the age of the ovum 

 when fertilized is probably justified ; while Hensen extends this notion to the 

 male element as well. The age of the parents is probably only of secondary 

 import, and the law of Hofacker and Sadler is not confirmed. 



VII-VIII. Theories of " comparative vigor " and the like must be dismissed; 

 while Starkweather's theory of the relative superiority of either sex, and of 

 the influence of this on the sex of the offspring, requires further analysis. 



IX-X. Darwin's position contains nothing novel, and has been superseded 

 by Diising's synthetic treatment and explanation of the self-regulating 

 numerical proportion of the sexes. 



X. From this point, after a note on the similar sex of "true " twins, we pass 

 to the experimental data and constructive treatment. 



LITERATURE. 



Berner. — Hj. Om Kjonsdannelsens Aarsager, En biologisk Studie (with 



numerous references). Christiania, 1883. 

 Darwin, C— The Descent of Man, Chap. VIII. Nos. 74, 75, 76, 77. 



The Variation of Animals and Plants under Domestication. Lond. 



Dising, C. — Die Regulierung des Geschlechtsverhaltnisses bei der 



Vermehrung der Menschen, Thiere, und Pflanzen. Jena, 1884 ; or, Jen. 



Zeitsch. f. Naturw., XVII., 1883. 

 Geddes, P. — As before. 

 Hensen, V. — Physiologie der Zeugung. Hermann's Handbuch der 



Physiologie, Bd. VI., pp. 304, with references to Ploss, Schultze, &c. 



Leipzig, 1 88 1. 

 His, W. — Theorien der geschlechtlichen Zeugung. Arch. f. Anthropologic 



Bde. IV. -VI. 

 Hofacker. — Ueber die Eigenschaften, welche sich bei Menschen und Thieren 



auf die Nachkommen vererben. Tubingen, 1828. 

 Laulanie, F.— Comptes Rendus, CI., pp. 593-5- ^85. 

 Rolph, W. H— As before. 



Roth, E. — Die Thatsachen der Verebung (historical). Berlin, 1885. 

 Pfluger, E.— Ueber die das Geschlecht bestimmenden Ursachen und die 



Geschlechts-verhaltnisse der Frosche. Arch. f. d. ges. Physiol. XXIX. 

 Sadler. — The Law of Population. London, 1830. 

 Schlechter. — Ueber die Ursachen welche das Geschlecht bestimmen. Rev. 



f. Tierheilkunde. Wien, 1884. Biol. Centralblt., IV., pp. 627-9. 

 Starkweather. — The Law of Sex. London, 1883. 

 Stieda.— Das Sexual Verhaitniss bei Geborenen. Strasburg, 1875. 

 Sutton, J. B. — General Pathology 7 . London, 1886. 



Thury.— Ueber das Gesctz der Erzeugung der Geschlechter. Leipzig, 1863. 

 Wappceus. — Allgemeine Bevolkerungs-Statistik. Leipzig, 1861. 



