ONTOGENESIS 229 



that the sex of the offspring corresponds to that 

 of the less vigorous parent. Almost as many 

 facts, however, favor the opposite opinion, that 

 it is the more vigorous parent that determines 

 the sex of the offspring. 



(c) By the nutrition of the parents. The whilom 

 popular theory of Schenk taught that the 

 nutrition of the mother was at the foundation 

 of sex determination. If, during pregnancy, 

 she was kept in the highest state of nutrition, 

 female offspring were more numerous; if, on 

 the other hand, her nutrition was kept below 

 par, there was greater likelihood of male off- 

 spring. 



In all three cases it would seem as though the 

 circumstance of the occurrence of both sexes 

 in cases of plural births would overthrow the 

 validity of the theory. Thus twins are fre- 

 quently of both sexes, and, among animals 

 simultaneously giving birth to many offspring 

 at the same time, the sexes are usually almost 

 equally divided. Moreover, these theories 

 could in no way be made to apply in the cases 

 of birds, fishes, insects, and still more lowly 

 creatures, where the eggs leave the body of the 

 mother and cannot be subsequently influenced 

 by her. 



B. That the sex of the individual is determined by 

 the nutritive conditions of early embryonal life. 

 These theories seem to be based upon the assump- 

 tion that every organism is either a sexual neuter 

 or a hermaphrodite during early embryonal de- 

 velopment, and that sex makes its appearance or 

 one or the other sex succeeds in preponderating 

 as development advances. Most of the investi- 

 gations upon this phase of the subject have 

 been performed upon animals with a prolonged 

 period of embryonal i.e., larval life. 



