'750 Bashford Dean Memorial Volume 



show through it. In the original, a spot in front of the embryo probably represents the 

 optical effect of an oil globule in the yolk mass. It has been removed. 



In Figure 59, plate V, the pattern of both arteries and veins is essentially the same as 

 in the preceding figure, but the yolk blastopore is smaller and some of the venules seem to 

 drain into an incomplete inner venous circle. This, perhaps, is an individual variation. 

 The venules are longer than those delineated in the preceding figure. The vitelline vein, 

 crossed by the tail of the embryo, may be seen leading forward to the yolk stalk which is 

 attached to the pectoral region of the embryo. 



Figure 60, plate V, shows right and left branches of the vitelline artery diverging 

 more widely than in the preceding stages; their extremities extend to the margin of the 

 figure. The yolk blastopore is reduced to a tiny circular area just behind the pelvic region 

 of the curved embryo. A venous circle is lacking, and the venules converge toward 

 irregular masses, colored red, closely surrounding the yolk blastopore. These masses 

 may, in part, represent pigment, but it seems likely that they consist mainly of extrav 

 asated blood. Some of the venules begin at the extreme lower edge of the figure. The 

 embryo lies partly on its right side, so that a blood vessel, presumably the vitelline vein, 

 appears to the left of its ventral surface. 



In Figure 61, plate V, the trunk and the two main branches of the vitelline artery 

 are more prominent than in any of the preceding figures; but the branches extend to the 

 opposite side of the egg, which is not represented by a drawing. The yolk blastopore has 

 completely disappeared. The vitelline vein receives two parallel main branches close to 

 the yolk stalk. The veins and venules have assumed a dendritic pattern. The round spot 

 underneath the middle of the embryo is probably the optical effect of an oil globule in the 

 yolk mass. 



The egg represented in Figure 62, plate V, is anomalous. It bears two embryos 

 (twins) each with its own vitelline artery and vein; but the two veins drain the same 

 nexus, into which all the venules empty. The unpaired vitelline arterial trunk leading 

 toward the top of the figure is longer than any shown in earlier stages. This artery ends 

 in the usual two branches, but the other artery passes to the margin of the figure and 

 cannot be traced further. 



In Figure 63, plate V, the vitelline artery passes to the opposite side of the egg 

 before branching. This figure, taken in connection with those that follow, indicates that 

 the arterial circle forms entirely on the hemisphere of the egg farther away from the yolk 

 stalk. The vitelline vein is still short and its manner of branching dendritic. 



Figure 64, plate VI, represents a stage slightly later than the preceding, though the 

 vitelline artery divides before reaching the upper part of the figure. Leading to the yolk 

 stalk, there are two main vitelline veins; the more anterior branches of these veins are the 

 strongest. This is an example of a tendency, by no means universal, for the vitelline 

 veins to occur in two groups, right and left respectively. Figure 65, plate VI, is perhaps 

 intended to represent the reverse side of the same egg, since the drawings of this plate 

 retain their original paired arrarigement; but a careful study shows that the two figures 



