26 



K. MITSUKUlii. 



sero-nmniolic connection, altliouuli the ])osition .sliown in Jnu". 71 

 appears to l)e tlie most normal. 



The l)ho(3cl-vessels that pass thi'ono-h the umbilicus at tliese later 

 stages, are arranged as in Fig. 75 (PI. IX.). The most anterior is 

 the vitelline vein, then comes the \itelline artery, after it tlie allantoic 

 artery and last of all the allantoic vein. The last three di\ ide int(j two, 

 the right and left brandies, soon after their exit from the umbilicus. 

 The vitelline artery is distril)uted over the surface of the yolk, but 

 the vitelline vein is somewhat peculiar: it is much larger than the 

 vitelline artery and while it receives branches from the surface of 

 the yolk, the main liulk of it enters right into the substance of 

 the yolk. This no doubt makes the acquisition of nutriment from 

 the yolk much easier. 



I may now proceed to describe the relations of the embryo, the 

 foetal membranes and the yolk shortly before hatching. (Figs. 71 

 and 71a PI. \U\. and Diag. VI. Pi. X.). 



Tlie yolk sac (Fig. 71«) is now reduced considerably in 

 size and the three lobes of the allantois have entirely enclosed it. 

 These three lobes never fuse witli one another, but are permanently 

 sejiarate. The seams that sejiarate them are roughly speaking 

 tri-radiite, the center being at the anterior end of the yolk-sac slightly 

 to the left (to our riglit as we view it from the ventral surface) of 

 the median ventral line. The seam that extends transversely from 

 the center towards (he right (to the left of the observer) se]>arates the 

 middle (phi«.'e<l in front of it) fivtm the right allantoic lobe (jilaced 

 behind it) and corresponds to the anterior constriction in Pig. 67. 

 Hence, at its distal end. is found the rio-ht set of the allantoic arteries 

 and veins. The seam that runs back from the center nearly parallel 

 with the median ventral line separates the left lobe (placed to its left 

 or to the ol)server's right) iVoni llic right lobe, and corresponds to the 



