554 
OBSERVATIONS ON THE 
exposed. An explanation, however, of this soon offered^ 
for, on plunging the knife into the liver, the blood gushed 
out in such quantities as presently to fill the whole abdo- 
minal cavity ; it seemed as if the entire mass of blood na- 
turally belonging to the animal had been accumulated in 
this viscus only. The real cause of death seems to me 
obscure ; but the facts are valuable in so far as they illus- 
trate the physiology of these organs. 
The observations I have had the honour to detail to the 
Society seem sufficient to establish, as a general theory, 
that the power of suspending respiration, possessed by 
aquatic animals, is connected with a peculiar formation of 
their venous system. An ingenious friend, Mr Thomas 
HoDGKiNs, has endeavoured to shew, that the spleen, in 
man, is intended as a reservoir for the blood, in cases of 
altered circulation ; but it is probable that the whole system 
of the vena port(£ assists in this function. Moreover, if this 
were really a function peculiar to the spleen, we ought to 
find this organ proportionally largely developed in aquatic 
animals, which is not the case. 
I have already remarked, that there exist valves at the 
mouths of the vence cav€£, where they expand into the right 
auricle of the heart. The physiology of these valves is not 
very well understood, and must necessarily remain obscure, 
from the circumstance of their being occasionally absent or 
present, without any general law explanatory of this fact 
having been traced. Every anatomist knows, that in man 
the Eustachian valve is sometimes very large in the adult, 
at other times scarcely perceptible. It exists in animals of 
various classes, without our being able to trace any con- 
necting physiological theory. 
In all the animals I have dissected, it has uniformly ap- 
peared to be strictly membranous, and to bear a close 
resemblance to other valves found in veins. It is incom- 
