370 INTRODUCTION TO CYTOLOGY 



quite "masculine ,: in their secondary sex characters early in the season, 

 become increasingly " feminine " toward the end of the season. Moreover, 

 the total percentage of females increases. By influencing storage, water 

 content, and the general metabolic condition of these eggs Riddle has 

 been able to induce experimentally an actual reversal of their natural sex 

 tendencies. Hence he concludes that sex is a quantitative, modifiable, 

 and "fluid" character; the two sexes do not represent two qualitatively 

 distinct, mutually exclusive properties, but are rather two conditions of 

 one general property — two levels in a continuous series of metabolic 

 states passing gradually one into another. Accordingly, if the two levels 

 normally maintained can be sufficiently altered a series of intergrades 

 between the two sexes and an alteration of the sex itself should be possible, 

 and this Riddle has apparently accomplished. 



On the basis of this metabolic theory of sex Riddle interprets the 

 results obtained by Miss King with toad eggs, by Hertwig with those of 

 t he frog, by Whitney and Shull with rotifers, and by other investigators 

 to be mentioned below. The correlation of high and low water content 

 with maleness and femaleness respectively in toads and frogs, and that of 

 change of food and increased oxygen supply with maleness in rotifers, are 

 held to be in harmony with similar correlations which have been shown to 

 exist in pigeons. 



The theory that sex is a quantitative, reversible state closely asso- 

 ciated with metabolic conditions is strongly supported by the researches of 

 Goldschmidt (1916a6, 1917), Banta (1916), and Lillie (1917). In the 

 gypsy moth, Lymantria dispar, which is cytologically heterogametic, 

 Goldschmidt has been able to induce experimentally a large series of "sex 

 intergrades " between the male and female conditions. It appears that an 

 individual of either sex, after beginning its development, may be made to 

 develop the characters of the other sex partially or completely, the degree 

 of alteration depending upon the time at which the change sets in. Gold- 

 schmidt concludes that normal individuals of both sexes must have both 

 sex capabilities, the sex manifested depending upon the relative strength 

 with which they are caused to act by certain conditions. He thinks it prob- 

 able that the hereditary characters have their material basis in enzymes 

 or substances of a similar nature, those associated with femaleness and 

 maleness being termed " gynase " and " andrase " respectively. Although 

 for a time he interpreted the behavior of the sexes in Lymantria on the basis 

 of Mendelian factors, he is now inclined to view this form of explanation 

 as inadequate. The chromosome behavior in these moths is not well 

 known, but breeding experiments with an intersexual female functioning 

 as a male show the results which would be expected on the assumption 

 thai she had the PTZ-chromosome constitution. This would mean that 

 the moth in question had had its sex reversed without any visible 

 change in its chromosome 1 complement, but this intrepretation awaits 

 cytological confirmation. 



