. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. SEX IN ANIMALS 543 exactly the same as that among Miss King's rats, males to 100 females. Among wide crosses of hybrid birds the percentage of males also appears to be abnormally high, but this can hardly be taken as in conformity with the data of King and JMinot, because iu birds the mode of sex-inheritance is exactly the reverse of that in mammals. Ac- cordingly these data should be regarded as confirmatory of the data from bison-cattle crosses, and those of Detlefsen with cavy species cros
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. SEX IN ANIMALS 543 exactly the same as that among Miss King's rats, males to 100 females. Among wide crosses of hybrid birds the percentage of males also appears to be abnormally high, but this can hardly be taken as in conformity with the data of King and JMinot, because iu birds the mode of sex-inheritance is exactly the reverse of that in mammals. Ac- cordingly these data should be regarded as confirmatory of the data from bison-cattle crosses, and those of Detlefsen with cavy species crosses. As another possible source of variation in the sex-ratio, mention must be made of the time of service with respect to the inception of the period of heat. Various theories of sex have from time to time been founded on heat relations, some maintaining that the products of con- ception in early heat were more often males, others that they were more often females. Pearl and Parshley have made an experimental-statisti- cal study of this question, the data of which are given in Table LXXII. These data were collected from farmers in the state of Maine, and represent all breeds and ages of cattle. Pearl and Parshley draw attention to the fact that they show a steady increase in the proportion of male births with later coitus. The question as to the general signifi- cance of this fact, they discuss at some length. In Table LXXIII is given the statistical treatment of these data. Only in one case, that Table LXXII.—The Effect of Service at Different Periods of Heat on the in Cattle {Data of Pearl and Parshley) Time of coitus Total ol^spring Sex of ofTspring Percentages Males Females Male births j Female births 100 females Early in heat 248 Middle of heat 125 Late in heat | 107 123 67 65 125 58 42 ± ± + Totals, all ! 480 2,55 225 + ]..54 113 3 Table LXXIII.—Statistical Treatment
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