Makch 12, 1915] 



SCIENCE 



401 



V. Finally, the importance of collateral 

 reading in the masterpieces of biological lit- 

 erature is strongly emphasized. 



At the St. Louis meeting of the American 

 Association of Anatomists, December 29, 1914, 

 the report of the committee on premedical 

 work in biology was approved by the associa- 

 tion; and the committee was continued with 

 instructions to submit the approved report to 

 the zoologists, and to secure their cooperation 

 in carrying- the work further. 



H. McE. Knower, Chairmcm 



SPECIAL ABTICLES 



SEX DETERMINATION AND SEX CONTROL IN 

 GUINEA-PIGS 



The observations, a short exposition of 

 which is given here, were made on guinea- 

 pigs, being used by Professor Stockard in he- 

 redity experiments. He very kindly placed 

 the material at my disposal for this study, and 

 I wish to express my appreciation of this 

 favor. 



These observations show that the sex of a 

 guinea-pig is determined sometimes by two 

 and sometimes by three factors, depending 

 upon whether the mother has previously born 

 young. 



The first factor " A " is the sex tendency of 

 the father. If the father has a male sex 

 tendency, his sons will have a female tend- 

 ency and his daughters a male tendency. If, 

 on the contrary, the father possesses a female 

 tendency, his sons will have male tendencies 

 and his daughters female tendencies. In 

 other words, sons exhibit the opposite and 

 the daughters the same tendency as the 

 father. 



The second factor " B " is the sex tendency 

 of the mother. A mother with a male tend- 

 ency gives her daughters a female and her 

 sons a male tendency. The mother with a fe- 

 male tendency gives her daughters a male 

 and her sons a female tendency. Thus the 

 transmission of the sex tendency from the fe- 

 male is also criss-cross in the same fashion as 

 that of the male. The females inherit like 

 tendencies from their father and the males like 



tendencies from their mother, whereas the 

 males inherit the reverse tendency of their 

 father and the females the reverse tendency 

 of their mother. 



The third factor " C " is confined to the 

 female and! is a change of sex tendency from 

 litter to litter. This change in tendency 

 manifests itself in the following way: 



If the first litter contains only males, the 

 mother acquires a female tendency for the 

 next litter and vice-versa. This new tend- 

 ency varies in strength, depending upon the 

 number of young of one sex contained in a 

 litter. The greater the number of males in a 

 litter, the stronger the female tendency will 

 be for the next litter. This tendency is still 

 more emphasized if the mother is successively 

 mated with males of a definite tendency, and 

 therefore forced to produce more and more 

 young of one sex. 



The tendency of the various animals of a 

 certain stock must first be ascertained in an 

 experimental manner; given a number of un- 

 determined males and females, each male must 

 be mated with all the females and each fe- 

 male with all the males. After all the ani- 

 mals have been tested in this way, the results 

 will show more males from some animals and 

 more females from others. If, now, the oil- 

 spring from these matings be grouped so as 

 to take those animals which have come from 

 more male producing fathers and their tend- 

 ency be tested, it will be found that from the 

 males more females will be produced and 

 from the females more males. Provided the 

 determination of the sex tendency for the 

 first set of animals was absolutely correct, 

 and if there was no other factor in action, the 

 proportion of males to females should be as 

 75 : 25 from male producing males mated with 

 females having diiferent tendencies, and from 

 female producing males the proportion is re- 

 versed. It is, however, very difficult to deter- 

 mine absolutely the sex tendency of an ani- 

 mal after only a few matings, and for this 

 reason, some animals supposed to have a male 

 tendency wiU probably have a weak female 

 tendency, and vice versa. 



In order to find with reasonable definiteness 



