382 



THE NEW INDIVIDUAL 



Part IV 



Fig. 19.17. A section of the two-celled stage of a human embryo taken from an 

 oviduct during an operation. (Courtesy, A. T. Hertig and Carnegie Institute of 

 Washington.) 



capillaries that join vessels that reach the embryonic placenta from the em- 

 bryo by way of the umbilical cord. Thus, there is a double circulation in the 

 placenta, an embryonic part in the villi and a maternal part in the reservoir 

 in which the villi are immersed. 



Carbon dioxide and other waste products of the embryo pass through the 

 membranes of the villi from the blood of the embryo into the blood of the 

 mother. Food and oxygen from the blood of the mother pass into that of the 

 embryo. 



By means of radioactive chemicals, it has been shown that the smaller 

 molecules of matter pass through the membranes of the villi, substances such 

 as salts, sugars, calcium, amino acids, and certain vitamins and hormones. 

 The Rh factor, an antigen or substance that causes agglutination (clumping 

 and sticking together of red blood cells), may be present in the blood of the 

 embryo. This may pass through the placenta into the mother's blood. If her 

 blood is negative to the Rh substance, it can stimulate the production of 

 antibodies which return to the embryo and destroy its red blood cells. 



There is no means of communication between the embryo and mother 

 except by substances such as those that have been named. Not a single nerve 

 passes from one individual to the other. In its psychology the embryo is as 

 independent of its environment as any other animal may be. 



Hormones. The placenta is not only a filter of foods going inward to the 

 embryo and waste products going out, but it also produces a series of hor- 

 mones. 



