The blood movement takes place, according to Pander, in 

 the following manner. The arterial division of the heart, 

 "with surprising speed and strength" of contracting, sends 

 the blood into the aorta. The push caused by the contraction 

 spreads the blood along the arteries, it then moves to the 

 venous branches and the terminal sinus. From the latter, 

 the blood returns to the heart through the descending and 

 ascending veins. 



"The features of blood circulation," Pander wrote, 



are so unusually magnificent that we invite 

 everybody who has any desire to investigate 

 nature not to miss the excellent chance given 

 by the incubated egg to try to enjoy this 

 excellent performance .... For this 

 purpose it is recommended to take an egg of 

 three days incubation, to open it in warm 

 water, and to transfer quickly the blastoderm 

 into a glass plate a little submerged in 

 water under a complex microscope with a large 

 optical field, and to observe under dripping 

 warm water which preserves the movement of 

 the blood. 37 



At the stage described, Pander thought that there was still 

 no portal vein. Oken responded that if the portal vein is 

 not actually present, then there should be mesenteric 

 vessels, or umbilical arteries; he reasonably asked whether 

 the veins accompanying them are to be considered the 

 mesenteric veins. 



The third stage of development of blood circulation 

 begins with the appearance of the chorion sac (h in 7B) in 

 which the umbilical vessels mainly develop. When this 

 organ dies off, the fourth stage of blood circulation 

 begins. 



Turning to the development of the amnion, Pander cited 

 his drawings, which yield explanations as "the descriptions 

 of the ideal sections." The explanations are given here in 



37. Ibid., p. 520, 



270 



