THE DETERMINATION OF SEX. 53 



SUMMARY 



1. Nutrition is one of the most important factors in determining sex. In 

 illustration, note {a) the experiments of Yung, which raised the percentage 

 of females from 56 to 92 by good feeding ; (/') the case of bees, where the 

 differences between queen and worker well illustrate the enormous results 

 of a slight nutritive advantage ; also the case of humble-bees, with three 

 successive broods increasing in nutritive prosperity and in femaleness ; {c) 

 Von Siebold's experiments with a wasp, which showed most females in 

 favoural)le conditions ; {(/) Aphides, in prosperity of summer, yield a 

 succession of parthenogenetic females, in cold and scarcity of autumn males 

 return ; {e) starved caterpillars of moths and butterflies become males ; (/) 

 Rolph's observations on crustaceans; {g) also the facts noted by Girou, 

 DUsing, and others, on the influence of good nourishment of mammalian 

 mothers in favouring female offspring ; (//) the hints of the same results 

 in the human species ; (/) the various observations in regard to plants which 

 favour the same general conclusion. 



2. As to the influence of temperature, favourable conditions again lend 

 to femaleness of oflspring, extremes to males. 



3. These factors are now added up, — [a) the nutrition, age, &c. , of 

 parents ; {/>) the condition of the sex elements ; {c) the environment of 

 embryo. 



4. The generalisation is thus reached, — anabolic conditions favour 

 preponderance of females, katabolic conditions tend to produce males. 



5. But females have been already seen to be more anabolic, and males 

 more katabolic. This view of sex is therefore confirmed. 



6. How does Weismann explain the determination of sex, which illus- 

 trates an outside influence penetrating to the reproductive cells ? 



LITERATURE. 



See works mentioned in Chapter III., especially those of Diising, 

 Geddes (article Sex, Ency. Brit.), Hensen, and Sutton; also those of 

 Eimer, Geddes, and Rolph in Chapter II. 

 DiJSlNG, C— As before ; also, Die experimentelle Priifung der Theorie von 



der Regulirung des Geschlechtsverhaltnisses. Jen. Zeitschr. f. 



Naturwiss. XIV., Supplement, 1885. 

 Heyer, F. — Untersuchungen iiber das Verhaltniss des Gcschlechtes bei 



einhiiusigen und zweihausigen Pflanzen, unter Beriicksichtigung des 



Geschlechtsverhaltnisses bei den Thieren und den Menschen, Ber. 



landwirthschaftl. Inst. Halle. V. 1884, pp. 1-152. 

 Meehan, T. — Relation of Heat to the Sexes of Flowers. Proc. Acad. 



Nat. Science, Philadelphia (1884), pp. 111-117. 

 Semper, C. — The Natural Conditions of Existence as they Affect Animal 



Life. Internat. Science Series, London, 1881. 

 Thomson, J. A. — Synthetic Summary of the Influence of the Environment 



upon the Organism. Proc. Roy. Phys. Soc. Edin.,_ IX. (1888), 



pp. 446-499. (Supplementary to Semper's work, with bibliography.) 

 The History and Theory of Heredity. Proc. Roy. Soc. Edin., 



1889, pp. 91-116, with bibliography. 



