Charles F. W. McClure 223 
+. In the rabbit embryo the portal vein (omphalomesenteric) on 
reaching the liver anastomoses directly with the left umbilical vein to 
form the ductus venosus Arantii, so that the latter, at a certain period 
of development, returns to the heart most of the blood that reaches the 
liver through the portal and left umbilical veins. In Didelphys, how- 
ever, no such direct anastomosis takes place between these two veins, but 
each vein is continued through the parenchyma of the liver in a separate 
channel which opens into the proximal end of the posteava independently 
of the other; a condition which, in some respects, resembles that met 
with in birds. 
So far as known to the writer, Broom is the only investigator who has 
hitherto described the umbilical and omphalomesenteric veins in the 
embryos of marsupials (Trichosurus) and, although his account is some- 
what fragmentary it conclusiyely shows, when compared with the above 
observations of the writer, that the plan of the embryonic hepatic circu- 
lation in marsupials not only differs from that of the higher mammals, 
but that there is also a difference even among the marsupials themselves. 
5. Abdominal veins are present in the 8 mm. embryos of Didelphys 
which resemble in all respects the abdominal veins of reptiles. They he 
in the mid-ventral body-walls, connect cranially with the umbilical veins 
at the umbilicus and caudally with the external iliaes. 
In conclusion, I may state that in 1902 I received a letter from Dr. 
J. P. Hill, of the University of Sydney, in which he was kind enough to 
send me a few rough sketches illustrating the development of the veins 
in Perameles. He specifically stated that the schemes were not drawn 
to scale and, as they represented only a series of preliminary observa- 
tions, he did not care to vouch for their accuracy in detail. The general 
conclusions which he drew from his observations are most interesting, 
and I quote them in full. “ From these rude schemes there can be no 
doubt as to the origin of the posteaval vein from an unpaired anterior 
portion and paired posterior portions which probably fuse as shown in 
the 17 mm. stage. The most interesting find to me was that of a defi- 
nite renal portal circulation in connection with the mesonephros.” 
These observations coincide with mine on Didelphys so far as the de- 
velopment of the caudal portion of the stem of the postcava is concerned. 
The presence of a definite renal portal system was not observed by the 
writer either in the Dasyurus embryo nor in any of the embryos of Di- 
delphys examined, but its presence in Perameles, however, further illus- 
trates the unexpected as well as unusual characters which one occasionally 
meets with in the embryo, as well as in the adult of the marsupials in 
general. Of these characters, so far as the venous system is concerned, 
