STUDIES ON THE CELLS OF CATTLE. 2QI 



gressive increase in the proportion of male young born. (2) 

 That in the extreme case this increase in the proportion of male 

 births is probably statistically significant and not to be attributed 

 to errors of random sampling. (3) That these modifications of 

 the sex ratio cannot be attributed to age differences or to any 

 other factor yet suggested. 



More recent and extensive data, however, according to Pearl 

 ('17) make the relation of time of service to sex extremely 

 doubtful. He says: "The apparent relation between these two 

 factors, which is believed by many breeders to exist and which 

 our earlier statistics appeared to indicate, seems now to be 

 purely accidental, and to have arisen only because of the com- 

 parative meagerness of the statistics on which the matter was 

 discussed." Sex in cattle is a matter of heredity, as is shown 

 by the results of this investigation, and remains a matter beyond 

 the control of the breeder; its ultimate control is problematical. 

 However, the suggestion of experimentally separating the two 

 types of spermatozoa, or destroying the one type without impair- 

 ing the nature of the other, does not appear to be entirely hope- 

 less. If this can be done, the problem of sex control will be 

 comparatively simple, since artificial insemination can be resorted 

 to. 



It appears to be a well-established fact that sex is determined 

 at the time of fertilization. Sex, like other characters of the 

 individual, has a definite factorial basis; and the factorial con- 

 stitution of the individual with respect to sex as well as to other 

 characters is fixed by the constitution of the two gametes which 

 unite to form the zygote. 



The dimorphic condition among the spermatozoa in many 

 of the lower animal forms is well known. Guyer pointed it out 

 in the rat ('10), and man ('10) ; other investigators have reported 

 it in several other mammals. Among the domestic mammals the 

 same condition has been clearly demonstrated in the pig (Wod- 

 sedalek, '13) and in the horse (Wodsedalek, '14). This study 

 on the sex cells of cattle shows that two types of spermatozoa are 

 also produced in the bull ; the one type at the time of fertilization 

 determining maleness and the other type determining femaleness. 

 The spermatozoan which determines femaleness is somewhat 



