PLATE VI 



FURTHER DEVELOPMENT OF THE VITELLINE VESSELS 



IN HETERODOHTUS JAPOKICUS 



Fig. 64. In this figure the embryo, for the first time in this series, lies at right angles to the direction of 

 the vitelline artery, showing that the embryo is able to rotate by twisting the yolk stalk. The 

 vitelline artery branches before reaching the margin of the figure. There are two vitelline 

 veins leading to the yolk stalk. 



Fig. 65. An egg in nearly the same stage as the preceding, showing the hemisphere opposite the one to 

 which the embryo is attached. The two main branches of the vitelline artery have joined an' 

 teriorly to form the arterial circle. 



Fig. 66. A later stage in which the arterial pattern resembles that shown in Figure 64, while the branching 

 of the vitelline veins is much more profuse and extensive. 



Fig. 67- Opposite hemisphere of the egg represented in the preceding figure, showing the convergence of 

 right and left sides of the arterial circle, which is profusely branched. 



Fig. 68. Here the embryo has been tilted to expose the yolk stalk, which shows the main trunk of the 

 vitelline veins. The vitelline artery does not branch before passing to the other hemisphere of 

 the egg. 



Fig. 69. The opposite hemisphere of the egg portrayed in the preceding figure. The arterial circle is nearly 

 obliterated by the coalescence of right and left sides. 



Fig. 70. The arterial and venous vitelline trunks are here seen pursuing parallel courses as they enter the 

 yolk stalk. The larger branches of the vitelhne vein occur in two groups, right and left. 



Fig. 71. The opposite hemisphere of the egg represented in the preceding figure. The right and left sides of 

 the arterial circle have coalesced to form an extension of the main arterial trunk. 



Fig. 72. Both arterial and venous patterns are similar to those shown in Figure 70, but the branching of the 

 veins is more profuse. 



Fig. 73. The opposite hemisphere of the egg depicted in the preceding figure, showing a symmetrical 

 branching of the vitelUne artery. 



Fig. 74. In this figure there is a fairly long vitelline vein having side branches. The embryo is in a stage 

 slightly older than the one represented in Figure 35, plate III. 



Fig. 75. Opposite hemisphere of the egg portrayed in the preceding figure. The pattern of the arterial 

 branching is nearly symmetrical, though quite unlike that shown in Figure 71. 



All the figures on this plate are in natural colors. The drawings are reproduced about natural size. 



