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The Determination of Sex in Animal Development. 



By 

 John Beard, D. Sc, 



University Lecturer in Comparative Embryology, Edinburgh. 



With plate 45 and 3 text-figares. 



"Das unaufhörliche Werden also, und nicht das 

 unaufhörliche Bestehen, ist das Ziel im Haushalte der 

 Natur." — Carl Eenst von Baer. 



"For indeed, the further we go and the more 

 closely we study, the more plainly is it brought home 

 to us, that we merely are waifs, shij^wrecked on the 

 ocean of Nature ; and ever and anon, from a sudden 

 wave more transpai'eut than others, there leaps forth 

 a fact, that in an instant confounds all we imagined 

 we knew." — Maurice Maeterlinck, The Life of 

 the Bee. 



Contents. 

 Preface. 

 Introduction. 

 I. Theses concerning Sex, Hermaphroditism, and Parthenogenesis. 

 II. The Gametes of the Metazoa. — The four Categories of Gametes 

 and the three Kinds of functional ones — Pseudo-Hermaphroditism. 



III. The supposed Influence of Fertilisation upon Sex. 



IV. The Manifestation of Sex. 

 V. The Basis of Sex. 



VI. Strasburger's Researches on Dioecious Plants. 

 VII. The Significance of the Reduction of Chromosomes. 

 VIII. The Determination of Sex. 

 IX. Concerning the Origin of Sex in the Metazoa. 

 X. The Regulation of Sex in Nature. 

 Summary of Chief Conclusions. 

 Description of Plate. 



Preface. 



In logical order the working out of the history of the germ-cells, 

 and, as it has turned out, of the problem of the determination of sex, 

 ought to have been the starting points for the course of research into 



