GERM-CELL HISTORY IN THE BROOK LAMPREY 105 



capacity of the male-producing eggs as compared with the female- 

 producing eggs." 



]More recently Whitney ('19) has reinvestigated the problem 

 relative to the effect of oxygen as male-producer in the rotifer, 

 and has come to conclusions opposite to those of Shull, namely, 

 that oxygen does not act as a factor in the production of male- 

 producers. The question cannot be considered fully settled. 



j. Variations in sex ratio. A variation in sex ratio might indi- 

 cate that sex is not irrevocably established at the time of fertili- 

 zation. It has been found that, in certain dioecious plants, 

 females are more commonly derived from seeds of one region and 

 males from those of another region. This may be due to differ- 

 ences in the metabolic activity of the two kinds of seeds, brought 

 about, possibly, by differences in the conditions of the environ- 

 ment under which they were raised. 



Montgomery ('08) found that there were 8.19 males for every 

 female in a count of 41,749 spiderlings. Out of the total of 127 

 cocoons, only eight showed a male ratio of less than one. Out 

 of the total number of eggs in the cocoons only 2871 failed to 

 hatch, and even though all of these should be assumed to be 

 female eggs, the ratio would not be appreciably altered and the 

 results cannot, therefore, be due to selective survival. Exam- 

 ples of this sort might be given by the score, and they are not 

 easy to explain on the hypothesis that the chromosomes are the 

 only and absolute sex determiners; for this hypothesis demands 

 that there should be an equal number of males and females pro- 

 duced. 



Pearl and Parshley ('13) have found that, in cattle, the sex of 

 the offspring is somewhat dependent upon the time of coitus. 

 Early in the heat the number of males to one hundred females 

 was 98.4; in the middle of heat the ratio was 115.5, and late in 

 heat it was 154.8. The conclusion is drawn that, granting the 

 presence of an X-chromosome, the results may be interpreted 

 by assuming that it is not a positive cause of sex differentiation, 

 but rather an inhibitor of the development of male characters — 

 two doses inhibits maleness, while one dose is insufficient. On 

 this hypothesis it is assumed that the general conditions of metab- 



