224 Maine Agricultural Experiment Station. 1918. 



entirely comparable being random samples of cattle twins "{ 

 have 22 where both are males, 38 where there are twins of ea 

 sex, and 15 where both are females, or there are 37 twins I 

 the same sex to 38 of opposite sex, a condition as close to 11 

 1 :2:i chance radio as could be well hoped for. Comparing t!i 

 with data presented by Nichols 8 where he found 234,497 wh<| 

 there were 2 males, 264, 098 where the twins were of opposl 

 sex, and 219,312 where the twins were both females or I 

 against the 1 like to 1 opposite sex of twins in cattle, the huml 

 family, have 1.7 like to 1 opposite sex. The excess of the In 

 sexed twins in the human family is known to be due to v. 

 identical twins, where two individuals of like sex come fnj 

 one egg. 



The figures given above show that cattle do not prodi 

 this excess over the 1 like sex to 1 opposite sex. Since this 

 true, it appears that in cattle the embroyological mechanism 

 such that it does not favor the production of identical twi 

 This conclusion is further borne out by evidence collected dil 

 ing the past year on the resemblance of the members of a p 

 of like sexed twins. 



(d) THE TIME AFTER THE APPEARANCE OF HEAT THAT SERV]| 

 IS MOST LIKELY TO CAUSE CONCEPTION TO TAKE PLACE ' 



Knowledge of problem (d) and (e) is so closely associat 

 to successful cattle raising as to be almost essential to 

 proper management of the herd. The analysis of large seri 

 of data on these problems collected through the cooperative 

 forts of the Maine Station and the Maine Cattle Breeders 

 therefore especially instructive. Table 7 presents the nee 

 sary data for the first of these problems. 



