20 



1 'liter; since thet blood vascular system woiild be less embarrassed and be more 

 free to act in cousequei:ce. 



. |But the allantois itself also participates in this action, the fluid it contains 

 enabling it to effect such rhythmical compression of the capillary plexuses 



TIG. 10. DIAGRAM OF YOUNG EMBRYO AND ITS VESSELS, showing circulation of umbilical 

 vesicles, and also that of allantois, beginning to be formed. (After Ualtou.) 



(Fig. 10). The following forcible illustration (Fig. 11) by the distinguished 

 biologistjat Jena will serve to impress the matter. At this early stage in develop- 

 ment (third week in gestation), it will be seen that pressure is increased at the 

 cardinal points, namely, vitellus (a), the body of the embryo (c), and allantois 



FIG. 11. HUMAN EMBRYO IN THE THIRD WEEK. A, large globular yelk-sack; f>, allantois; 

 c, amnion ; d, tufted cborion. There are yet limbs. (After llueckel.) 



(b). As the embryo and allantois are elaborated out of the material in the 

 vitellus, this would explain the greater accumulation of fluid in this locality for 

 compelling circulation toward those two points, whilst the rhythmical contrac- 

 tions of the yelk sac should greatly expedite it. For increasing circulation 



