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THE AMERICAN NATURALIST [Vol. XLI 



mination of sex, we will at the same time acquire experimental 

 data on the question of a period of sexual indifference in the devel- 

 opment of the individual. If sex is determined, as appears prob- 

 able from the statistical data, at the time of fertiUzation, it is 

 difficult to conceive of a period of real sexual indifference in the 

 histor}' of the individual. But if we can influence the sex of an 

 individual after fertilization of the ovum, we will at the same time 

 demonstrate a period of sexual indifference in development. 



The bearing of artificial parthenogenesis on the problem of sex. 

 — In a personal communication to the writer, Dr. Woelfel has 

 suggested that if, by any means other than fertilization by a sperma- 

 tozoon, we are able to cause an ovum of an animal which normally 

 reproduces bisexually to develop to sexual maturity, we will have a 

 demonstration that one parent plays a purely asexual role in the 

 production of sex. This conclusion, however, does not follow 

 necessarily. Moreover no individual arising by artificial partheno- 

 genesis has as yet grown to sexual maturity. Whether this failure 

 of normal development is due to improper nutrition of the young 

 or to a lack of some essential detail in fertilization cannot, perhaps, 

 be stated at present. One is inclined to regard the production of 

 a sexually mature individual, whicli may in its turn reproduce, and 

 the transmission of certain heivditaiy characteristics to the off- 

 spring as two essential details of inuli/ation. Until these phe- 

 nomena have been imitated by artificial means, one is loath to 



by artificial parthenogenesis (Loeb :06). The study to artificial 

 parthenogenesis may have an important bearing upon the deter- 

 mination of sex, but the true significance of the work already done 

 is not apparent. 



VI. Summary and Coxcu sioxs. 



The statistical study of the distribution of sex in man sliows 

 that there is a sHght but constant excess of male Ijirtlis. The 

 greater mortality of the males leads to a preponderance of females 

 in old age. 



There are certain unavoidable errors in the statistics, the two 

 most serious being (1) incompleteness, and (2) disregard of dupli- 



