Vascular System of Bdellostoma dombeyt. 4 
the extension forward of the sub-chordal dorsal aorta into the 
head region as the wertebralis tmpar (vertebralis impar capitis, 
of Miiller; cranial aorta, of Ayers) is probably a primitive 
character. This vessel occurs in Chlamydoselachus, as well 
as the Cyclostomata. 
Miiller describes a vein in Bdellostoma forsteri which runs 
from the right pronephros to the posterior cardinal. Only 
once have I found a similar vessel in Bdellostoma dombeyi. 
The vein which he describes from the intestine to the common 
posterior cardinal is also apparently lacking in Bdellostoma 
dombeyi. 
In Petromyzon, as in most Vertebrates, but unlike Bdello- 
stoma, the genital veins open into the posterior cardinals 
instead of the supra-intestinal vein. "The difference in size 
between the right and left posterior cardinals is only one 
example of the great asymmetry of the venous system which 
is so characteristic of Bdellostoma. 
The sub-intestinal vein* is the homologue of the large 
ventral vein in Amphioxus, and the embryonic sub-intes- 
tinal vein of higher vertebrates. Judging from the develop- 
ment of Petromyzon (Goette, Entwickelungsgeschichte des 
Flussneunauges) and other forms, the sub-intestinal vein at 
first probably supplied the entire intestine, and was continued 
posteriorly into the caudal vein. The connection of the 
caudal vein with the posterior cardinals is very probably 
here, as elsewhere, a secondary arrangement. The reduction 
in the size and extent of the sub-intestinal vein is correlated 
with the development of the supra-intestinal vein. It is 
interesting to note that in Bdellostoma the sub-intestinal vein 
does not break up into capillaries in the liver to form a portal 
system, although it runs over the surface of, and even ¢hrough 
the liver tissue. This is evidently an extremely primitive 
character, for the same relation is found in the early emdéry- 
onic development of the same vessel in Petromyzon (Goette, 
loc. cit.), and all higher Vertebrates. According to Willey 
(“Amphioxus and the Ancestry of the Vertebrates’’) it is 
yet doubtful whether the sub-intestinal vein in Amphioxus 
forms a ¢rue capillary portal system, or merely passes through 
*It is a remarkable fact that the presence of this vein in Bdellostoma has appar- 
ently been overlooked heretofore by all observers, including Johannes Miller. 
29 
