L26 



THE AMERICAN NATURALIST [Vol. LIV 



The conviction that not all eggs that are ovulated are 

 fertilized is borne upon one who compares the number of 

 corpora lutea in mammals that have large litters and the 

 number of embryos that one finds in the uterus. I have 

 recently made a number of counts in this respect in the 

 case of sows and give below results in tabular form: 



Thus from 34 corpora lutea, or 34 eggs expelled, only 

 22 embryos were found, counting only those which had 

 reached a length of 2 cm., at whicli stage the chorion is 

 already so large that it seems improbable that it should 

 have been overlooked. 



There is some reason for thinking that in humans also 

 a certain proportion of the eggs ovulated fail of fertiliza- 

 tion even in families in which there is no prudential re- 

 striction—in whicli the size of the families indicates a 

 probability that nearly the maximum number of eggs 

 became fertilized. Conclusions are fortified by the ex- 

 amination of a good genealogy including families of chil- 

 dren born in the latter half of the eighteenth and the early 

 part of the nineteenth centuries. Thus in a genealogy of 

 the Gorton family, seventh generation, the intervals in 

 round years between births in various fraternities (all 

 related as cousins, are : 



13 children— 3, 1, 1, 5, 1, 2, 2, 2, 2, 2, 1, 5; all born 1795- 

 1821. 



10 children— 2, 2, 2, 2, 2, 3, 2, 2, 2. In this case there is no 



unexpectedly large interval. 



11 children— 2, 2, 2, 2, 2, 2, 2, 2, 1, 5. 



6 children— 4, 2, 4, 3, 4; all born between 1792-1809. 

 8 children— 2, 2, 2, 2, 2, 5, 2 ; all born between 1796-1813. 

 13 children— 1, 2, 1, 2, 2, 2, 3, 3, 3, 2, 2, 4. In this case also 



