HEREDITY 795 



on certain positive and indisputable facts : The nuclei of the cells of 

 each and every species contain a definite number of chromosomes 

 peculiar to such species and always divisible by two. In mitosis, the 

 chromosomes of the mother-cells split and one-half goes to each daugh- 

 ter-cell. Maturation of the ovum involves the throwing off of one-half 

 the chromosomes in the polar bodies. The final phase of spermatogenesis 

 involves the division of chromosomes so that the spermatozoid has but 

 one-half the number contained in ordinary cells. When the two cells 

 meet, the egg is fertilized by the union of the egg-nucleus with the 

 sperm-nucleus, the resulting cleavage-nucleus containing the full num- 

 ber of chromosomes ; but if these two nuclei do not meet and unite, the 

 cells die. The fertilized egg, therefore, contains chromosomes derived 

 equally from the male and from the female. These characters and 

 this behavior, being peculiar to and confined to chromatin and invariable 

 in all forms of life, high or low, point almost conclusively to this sub- 

 stance as the medium of hereditary transmission; but they are not 

 favorable to the theory of transmission of acquired qualities. A fuller 

 discussion, however, of this subject would be out of place in this work. 



A peculiar and, it seems to be, an inexplicable fact is that previous 

 pregnancies have an influence on offspring. This is well known to 

 breeders of animals. If a pure-blooded mare or bitch has been once 

 covered by an inferior male, in subsequent fecundations the young are 

 likely to partake of the character of the first male, even if bred afterward 

 to males of unimpeachable pedigree. The same influence is sometimes 

 observed in the human subject. A woman may have, by a second hus- 

 band, children who resemble a former husband, and this is particularly 

 well marked in certain instances by the color of the hair and eyes. 

 A white woman who has had children by a negro may subsequently bear 

 children to a white man, these children presenting some of the peculi- 

 arities of the negro race. 



Superfecundation of course does not come in the category of in- 

 fluences just mentioned. It is not infrequent to observe twins, when 

 two males have had access to the female, that are entirely distinct from 

 each other in their physical characters a fact readily explained by the 

 assumption that two ova have been separately fecundated. This view 

 is sustained by observation and experiment, and many illustrative cases 

 are on record. . 



The following communication was received in January, 1869, from 

 Dr. John H. Janeway, Assistant Surgeon, U.S.A., and it illustrates 

 Superfecundation in the human subject; or at least that was the view 

 taken by the negro father : 



" Frances Hunt, a freedwoman, aged thirty-five years, gave birth to 



