242 BIOLOGY: GENERAL AND MEDICAL 



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. 



Mrs. Treat experimented with caterpillars, and 

 found that when they were half-starved they 

 subsequently transformed into male insects. 



E. Young found that tadpoles kept under 

 normal conditions developed into sexually perfect 

 frogs in the proportions of 43 males to 57 females. 

 If, however, they were given an abundant flesh 

 diet, the percentage of males was greatly in- 

 creased. 



It is well known that aphides produce only 

 females during the summer months when the 

 conditions of nutrition are good, but also produce 

 males when the less favorable conditions of 

 autumn come on. 



Maupas and others have found that rotiers and 

 certain crustaceans appear to produce excessive 

 numbers of females in the presence of abundant 

 nutrition. 



Careful consideration of these findings will 

 show that in every case the conclusions are based 

 upon some kind of misinterpretation of the facts, 

 . and in most of them the factor of selective mor- 

 tality has not been given proper attention. 



