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THE AMERICAN NATURALIST [Vol. XLIII 



occur per annum and that the ovaries normally function alter- 

 nately, one need know further merely the date of birth and sex 

 of the previous child to compute the sex of the coming child. It 

 is evident that the ovulation in the same months varies in suc- 

 cessive years (due to the fact that there are 13 ovulations). 

 From this point then we can work to the tenth month previous 

 to the expected birth. Hence "if children are born in the same 

 m on tli an odd number of years apart they are of opposite sex; if 



I ». 1 s;i . Accordingly then the "production of sex at will must 

 consist in avoiding any allempt at fertilization in the months 

 during which an ovum is produced of the sex not desired. Dr. 

 Dawson believes it possible that some day by means of some 

 modification of the Kimtgen or other rays, we may actually see 

 an ovary ovulate. At present there appears no way of deter- 

 mining the sex of the first-born. 



The hook as a whole furnishes entertaining and suggestive 

 reading. One leaves it unconvinced, hut stimulated perhaps to 

 test the theory by careful observations of his own clinical mate- 

 rials. One feels, however, that the author is not justified in his 

 extreme position that even higher vertebrates can teach us noth- 

 ing with respect to the cause of sex and heredity in man. Surely 

 one trained in general biology, especially cytology and compara- 

 tive embryology can not accept the "theory" as anything more 

 than an unverified hypothesis. Of course "the array of clinical 

 facts at first seems to give the theory a semblance of solidity; 

 but this is rapidly dispelled by the arbitrary disposition made of 

 numerous exceptions. By the same methods it would probably 

 be as easy to prove the reverse position, t. e., that females come 

 from the right ovary and males from the left. The problem of 

 sex can never be solved by the method of collecting clinical ma- 

 terials alone— and Dr. Dawson's book represents perhaps the 

 last effort at such a solution. Clinical materials will always be 



much in the male gametes as in the female, and its final elucida- 

 tion seems indicated along the lines of a cytological (chromo- 



II. E. Jordan. 



