268 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
the veins in these two types Zumstein, 96 . 1 , 97 . 1 , has shown that 
the general course of the development is the same as in the pig, 
the mesonephric veins arising in the same way by the median fusion 
of the cardinals for a short distance. But as regards the size of the 
veins there is a marked difference from the pig. Thus in human 
embryos of 14 and 16 mm. the cardinal veins are not only smaller 
in width than the umbilical veins but smaller even than the dorsal 
aorta,— see Zumstein, 96 . 1 , p. 592-593. So also in the Guinea pig 
the relatively small size of the cardinal veins is recorded by Zumstein, 
97 . 1 , in his figures 5-12, from embryos of 18-24 days. These 
observations justify the inference of a direct correlation between 
the functional activity of the mesonephroi on the one hand and the 
size of the two pairs of veins and of the allantois on the other. 
The character of the circulation within the Wolffian bodies is not 
yet quite clear, for, although the connection of the blood channels 
between the tubules with veins is easily determined, the pathways 
of the arterial inflow are obscure. One sees readily the small 
arteries, which bring the blood from the aorta directly to the glo¬ 
meruli. I have not studied the arterial supply carefully, and can 
therefore only state that the arteries running to the glomeruli are 
the only mesonephric arteries which I have noticed, without how¬ 
ever being able to affirm that no others are present. If my suppo¬ 
sition as to the vascular arrangements are correct, then the course 
of the circulation must be from the aorta through the numerous 
small glomerular arteries, into the glomeruli, from the glomeruli 
into the intertubular vessels of the mesonephros, and thence into 
either the mesonephric or the cardinal veins. 
The intertubular vessels of the mesonephros of the pig are highly 
characteristic. They communicate freely with one another and 
with the veins, and they are in no sense capillaries. In Figures 1, 2, 
3, and 4, the representation of the Wolffian body is in each case in 
so far diagrammatic that many details are omitted, including most 
of the blood spaces. Fig. 6 is from a drawing much magnified of 
a small part of the left Wolffian body (to the right in the figure) 
of Fig. 3. It illustrates the character of all the intertubular vessels. 
Their walls consist for the most part solely of a thin endothelium, so 
thin as to be merely a line except where the nuclei are lodged; the 
nuclei are large, granular, and protuberant, and are indeed similar 
to those of the adult vascular endothelium, although conspicuously 
less flattened. This endothelium, endo , lies for the most part 
