PROBLEMS IN OBSTETRICS AND GYNECOLOGY 391 



element must be entirely eliminated in the determination of sex. 

 B. S. Schultze advanced the view that there are two kinds of ovums, 

 one of which may give rise to males, the other to females, but there 

 has been no proof of such a differentiation in the higher forms of 

 life. In several low organisms, however, it appears that these two 

 varieties (of ovums) exist. Thus Korschelt describes two kinds of 

 ovums in the ovaries of the worm Dinophilus opatris; one of large 

 oval shape, developing into females, the other small and round, 

 becoming males. 



With regard to the determination of sex by influences brought to 

 bear either upon parents, the sexual elements, or embryos, many 

 observations have been made, but trustworthy conclusions may be 

 derived only from the study of comparatively low organisms. The 

 influence of nutrition is thus considered of great importance in de- 

 termining sex. As illustrations may be noted the variations in the 

 sex of frogs associated with changes in the nutriment supplied to 

 the young tadpoles. Yung found that when the latter were left to 

 themselves the percentage of females was slightly in the majority, 

 but when very rich food was supplied, 92 females to 8 males in every 

 hundred were produced. In the case of bees it seems evident that the 

 influence which decides whether the offspring of the fertilized ovums 

 shall become queens or workers is the nature of the food-supply. 

 Rich and abundant diet develops queens; plain and scanty food 

 leads to the production of workers, in whom reproductive organs 

 are undeveloped. Very interesting observations have been made 

 upon plant-lice or aphides. In the warm months when food is plenty 

 they reproduce by parthenogenesis, the offspring being entirely 

 female. When colder weather and scantier food appear there is sexual 

 reproduction and an offspring of males. In the artificial life of a 

 well-kept greenhouse, these phases may be repeated at the will of 

 the observer, by varying the nutrition. So far as the temperature is 

 concerned, Geddes and Thomson state that experiments point to the 

 conclusion that favorable conditions tend to femaleness and extremes 

 to maleness of offspring. As regards higher forms of life, it is im- 

 possible to estimate the importance of nutrition, temperature, etc., 

 in the determination of sex, while as regards mammalians this field 

 of inquiry is as yet entirely speculative. 



From what is known of the early embryology of many invertebrates 

 and some of the lower vertebrates, it would appear that their early 

 embryonic life is one of indeterminate character so far as sex is con- 

 cerned, during which various conditions, e. g., nutriment, tempera- 

 ture, moisture, light, may act so as to produce maleness or female- 

 ness according to their abundance or deficiency. Whereas, in the 

 higher vertebrates, the period of embryonic sexual indeterminateness 

 (if any) is very short, and so far as is known no influence can be 



