SEX IN ANIMALS 543 
exactly the same as that among Miss King’s rats, 119.2 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 Minot, because in 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 LX XII. 
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 LX XIII is 
given the statistical treatment of these data. Only in one case, that 
Taste LXXII.—Tue Errecr or Service at DirrerENt Periops or Heat on THE 
SEX-RATIO IN CaTTLE (Data of Pearl and Parshley) 
ae | Sex of offspring Percentages eee 
: . ta eo 
Time of coitus offspting | | 100 females 
| Males | Females Male births | | Temale births 
Early in heat....... | 248 | 123 | 125 | 49.6042.14] 50.40 98.4 
Middle of heat..... | 125 67 | 58 53.60 + 3.01 46.40 115.5 
Late in heat........| 107 | 65 | 42 | 60.7543 19] 39.25 | 184.8 
Totals, all periods...| 480 | 255 | 225 | 53.13 + 1.54 | 46.87 113.3 
Taste LXXIII.—StatisticaL TREATMENT OF THE SEX-RATIOS OF TaBLE LXXII 
(Data of Pearl and Parshley) 
| Odds against chance 
ifferenc 
Groups’ compared | Difference BonaTTence 
Percentage of male births | 
Late in heat and early in heat...............) 11.15 + 3.84 18.80 to 1 
Late in heat and middle of heat............. | 7.15 + 4.39 2.69 to 1 
| 4.00 + 3.69 1.15 tol 
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