SEX IN LIVING FORMS 111 



food, until it has attained the weight of ten pounds. 

 After this, it will occasionally insert its head for the 

 purpose of sucking, notwithstanding another fetus may 

 have been deposited in the pouch ; for the latter attaches 

 itself to a different nipple from the one which has pre- 

 viously been in use." 



Uterine Life.— The uterine life of the new indi- 

 vidual begins with the impregnation of the ovum, which 

 occurs the instant it is brought in contact with the zoo- 

 sperms of the male. While in the uterus, the young 

 life is supported wholly by the mother. She is obliged 

 to provide not only for her own sustenance, but for the 

 maintenance of her child. And she must not only eat 

 for it, but breathe for it as well, since it requires a 

 constant and adequate supply of oxygen before birth 

 as much as afterward. 



How the Unborn Infant Breathes.— Oxygen and 

 nutriment are both supplied to it through the medium 

 of an organ called the placenta, which is a spongy 

 growth, composed almost entirely of blood-vessels, and 

 is developed upon the inner wall of the uterus, at the 

 point where the ovum attaches itself after fecundation. 

 The growing fetus is connected with this vascular organ 

 by means of a sort of cable, called the umbilical cord. 

 The cord is almost entirely composed of blood-vessels, 

 which convey the blood of the fetus to the placenta, and 

 return it again. The fetal blood does not mix with 

 that of the mother, but receives oxygen and nourish- 

 ment from it by absorption through the thin walls 

 which alone separate it from the mother's blood. 



The umbilical cord contains no nerves, as there is 

 no nervous connection between the mother and the 

 child. The only way in which the child can be influ- 

 enced by the mother is through the medium of the 



