241 
sure when it enters the arterioles of the rete, as is shown by the 
character of the arteriolar endothelium in this region, this being trans- 
formed presumably by the strong contraction of the arteriolar walls 
(15, Fig. 32, pl. IV). 
As to the function of the rete mirabile duplex, unless we can 
suppose that the gland so influences the blood in its immediate vicinity 
as to enable this, on returning through the venous capillaries of the 
rete, to cause in its turn the plasma of the arterial blood in the 
adjacent arterioles to take up more oxygen in solution from the 
corpuscles than it otherwise would, I can offer no suggestion as to 
its exact function. That some substance diffuses from the venous 
capillaries into the arterial and that this substance has something to 
do with the supply of oxygen to the gas gland cells seem to me to 
be assumptions warranted by the very structure of the rete, but the 
details of this process can only be investigated by someone better 
acquainted with physiological methods than myself. 
In conclusion I may point out that so long ago as 1835, EscH- 
RICHT and MULLER (2) described and figured in detail the remarkable 
duplex retia mirabilia, apparently comparable in all respects with those 
of the gas bladder, to be found in connection with the hepatic portal 
veins of the Tunny. The whole of the blood coming from the walls 
of the gut has to pass through the venous capillaries of these retia 
on its way to the liver, the arterial capillaries of the retia being 
formed by branches of the arteries supplying the gut wall. These 
retia of the Tunny, besides being exactly comparable in structure 
with those of the gas bladder, are moreover, in all probability, homo- 
logous with them, since in both cases; the venous capillaries run 
from the gut wall (the bladder is but an outgrowth of the gut) into 
the liver and the arterial capillaries arise from the gut arteries. These 
retia mirabilia of the Tunny also present a problem for physiologists. 
It may be mentioned that most or all of the other kinds of retia 
mirabilia described, e. g. the so-called “‘choroid gland” on the eye- 
ball of teleost fishes and the ramifications on the internal carotid ar- 
teries under the brain of the cow and many other mammals, are not 
comparable in detail with the retia mirabilia I have described. 
Literature. 
1) Byxowsx1, L., und Nussavum, J., Beiträge zur Morphologie des para- 
sitischen Knochenfisches Fierasper Cuv. Bull. Acad. Sc. Cracovie, 
1904, p. 409. 
Anat. Anz. Bd. 40. Aufsätze. 16 
