238 HEREDITY AND SEX 



tions that have been made out in the armadillo. 

 Jehring first reported that all the young of a single 

 litter are of the same sex (Fig. 111). The statement 

 has been verified by Newman and by Patterson on a 

 large scale. In addition they have found, first, that 

 only one egg leaves the ovary at each gestative period ; 

 and second, that from the egg four embryos are pro- 



FiG. 111. — Nine-banded Armadillo. Four identical twins with a 

 common placenta. (After Newman and Patterson.) 



duced (Fig. 112). The material out of which they 

 develop separates from the rest of the embryonic 

 tissue at a very early stage. The four embryos are 

 identical quadruplets in the sense that they are more 

 like each other than like the embryos of any other 

 litter, or even more like each other than they are to 

 their own mother. 



The second source of evidence concerning sex-deter- 



