230 BIOLOGY: GENERAL AND MEDICAL 



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. 



C. That sex-determination depends upon the age 

 of the ovum at the time of fertilization. 



Thury (1863) and Busing (1883) taught that 

 when the ovum was fertilized soon after ovula- 

 tion, it developed into a female; if long after 

 ovulation, into a male. 



Hensen was of the opinion that females re- 

 sulted when both ova and spermatozoa were in 

 the most active condition at the time of fertiliza- 

 tion. 



Vernon, in cross fertilizing certain echinoderms, 

 thought that the fresher gamete exerted the 

 greater influence in sex determination. 



D. That sex determination depends upon certain 

 conditions of fertilization. 



