THE PLACENTA. 383 



editions of this book, and explained it in the drawing now 

 given in Fig. 137. I based the statement on a very apt 

 deduction. For as the general form and the finer structure 

 of the placenta is entirely similar in Man and in Apes, 

 the origin of the organ could not be different in the two 

 cases. As, however, the bladder-like form of the allantois 

 of the human being had never been directly observed, I was 

 gravely accused by Wilhelm His of falsifying science. His 

 stated that " it is known that the allantois in the human 

 being is never seen in the bladder-like form " (!). Luckily 

 for me, this " never visible " bladder form was actually seen 

 by Professor Krause of Gottingen in the following year 

 (1875), and a drawing of it, reproduced in Fig. 133, was 

 given. ^'^^ 



When the bladder-shaped human allantois has reached 

 the inner wall of the tufted membrane {chorion), spreading 

 itself flatly over the latter, it forms the placenta, which is 

 very important to the nourishment of the germ. The stalk 

 of the allantois, which connects the embryo with the 

 placenta, and carries the large blood-vessels of the navel 

 from the former to the latter, is enveloped by the amnion, 

 and, together with the amnion-sheath, forms the so-called 

 navel-cord (Fig. 138, a s). The large network of blood- 

 filled vessels of the embryonic allantois attaches itself 

 closely to the mucous membrane of the maternal uterus, 

 and the partition wall between the blood-vessels of the 

 mother and those of the child grows very much thinner, 

 thus giving rise to the remarkable apparatus for nourishing 

 the embryonic body which we call the placenta, and to 

 which we shall refer hereafter. (Of Chapter XIX.) At 

 present, I will speak of it only in connection with the fact 



