FECUNDATION. 797 



constricted at its base, and is finally separated in the form of a globule. A 

 second polar globule is afterward formed in the same way. 



That portion of the altered germinal vesicle which remains embedded in 

 the vitellus is called the female pronucleus. At the point where the polar 

 globules are separated, a single spermatozoid penetrates the vitellus. The 

 head and intermediate segment of the spermatozoid become surrounded with 

 a star, swell up and form the male pronucleus. The male pronucleus unites 

 with the female pronucleus, and fecundation is complete. The union of the 

 male with the female pronucleus forms a body which passes downward into 

 the substance of the vitellus and is called the vitelline nucleus. The furrow 

 which marks the beginning of segmentation of the vitellus is always ob- 

 served at the point of separation of the polar globules. 



Hereditary Transmission, Superfecundation etc. The first question 

 which naturally arises relates to the conditions which determine the sex 

 of offspring. Statistics show the proportions between male and female 

 births ; but nothing has ever been done in the way of procreating male or 

 female children at will. According to Longet, the proportion of male to 

 female births is about 104 to 105, these figures presenting certain modifica- 

 tions under varying conditions of climate, season, nutrition etc. It has been 

 shown, by observations upon certain of the inferior animals, that the pre- 

 ponderance of sex in births bears a certain relation to the vigor and age of 

 the parents ; and that old and feeble females fecundated by young and vig- 

 orous males produce a greater number of males, and vice versa ; but no 

 exact laws of this kind have been found applicable to the human subject. 



No definite rule can be laid down with regard to the transmission of 

 mental or physical peculiarities to offspring. Sometimes the progeny as- 

 sumes more the character of the male than of the female parent, and some- 

 times the reverse is the case, without any reference to the sex of the child ; 

 sometimes there appears to be no such relation ; and occasionally peculiari- 

 ties are observed, derived apparently from grandparents. This is true with 

 regard to pathological as well as physiological peculiarities, as in the inher- 

 ited tendencies to certain diseases, malformations etc. 



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

 nancies have an influence upon offspring. This is well known to breeders 

 of animals. If pure-blooded mares or bitches have 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 they be afterward bred with males 

 of unimpeachable pedigree. The same influence is observed in the human 

 subject. A woman may have, by a second husband, 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 unmistakable peculiarities of the negro race. 



Superfecundation of course does not come in the category of influences 

 just mentioned. It is not infrequent to observe twins, when two males have 

 had access to the female, which are entirely distinct from each other in their 

 52 



