166 Venous System of Didelphys Marsupialis (L) 
agent that, with the usual after-treatment, will fix the tissues of the 
older pouch young avithout, at the same time, producing a considerable 
shrinkage. Although I have not yet had the opportunity of trying this 
method, I am inclined to believe that shrinkage can only be avoided by 
removing the epitrichium before the pouch young are placed in the fixing 
agent. 
Two methods of staining which proved to be most satisfactory for the 
study of blood vessels were a combination of Delafield’s hematoxylin 
and picric acid and one of bleu de Lyon and safranin. 
It is evident from the recent investigations of Lewis, 02, that the de- 
velopment of the postcaval vein in mammals cannot be adequately con- 
sidered without taking into account the réle played by the subeardinal 
veins, since he has shown that a portion of the right subcardinal 
in the rabbit enters into its formation. Lewis’ description of the sub- 
cardinal veins and his conclusions regarding the origin of the posteava 
in the rabbit, are given in the following quotation from his paper 
(page 241): 
“Small vessels from the mesentery pass into the cardinals. They 
anastomose in front of the aorta with vessels of the other side. They 
form a longitudinal anastomosis parallel with the cardinal vein, with 
which it is connected by numerous short veins, and from which it is sep- 
arated by a line of mesonephrie arteries. This longitudinal vessel con- 
nected with the cardinal vein at both ends, and bilaterally symmetrical in 
its early stages is the subcardinal vein.” 
“The cross connections between the subcardinal veins give place to a 
single large cross anastomosis caudad to the origin of the superior mesen- 
teric artery. Above this anastomosis the right subcardinal connects with 
the liver and rapidly enlarges; the left subcardinal becomes very small— 
Hochstetter says that it forms the left suprarenal of the adult. Below 
the anastomosis the subeardinals cease to exist as veins; they may persist 
as lymph spaces.” 
“'The vena cava inferior is a compound vessel composed of parts of 
the heart, the vena hepatica communis, the hepatic sinusoids, the upper 
part of the right subecardinal, and the lower part of the right cardinal 
vein.” 
Miller, 03, under the direction of the writer, has followed the develop- 
ment of the posteaval vein in birds and has likewise noted and described 
a system of veins in the embryo which corresponds exactly to that de- 
scribed by Lewis in the rabbit as the subcardinal system of veins. He 
also found in birds that a portion of the right subcardinal vein, as in 
the rabbit, enters into the formation of the adult postcava and that, in 
