328 Miller—The Anatomy of the Heart of Cambarus. 
pericardium, the pericardial sinus or the pericardial chamber, 
while the pulsating organ is termed the heart. 
The heart does not lie free in the cavity, but is attached to 
its walls by ligaments; while running out from the anterior and 
posterior ends are the blood-vessels (arteries), which penetrate 
the walls of the cavity and carry the blood into the general cir¬ 
culation. 
A more exact nomenclature demands, it seems to me, that the 
cavity be called “auricle,” and the pulsating organ “ventricle,” 
as this corresponds more accurately to the functions of the 
parts. 2 
The blood brought from the branchiae into the pericardial 
chamber passes at once into the pulsating organ, from which it 
is driven into the general circulation by its strong contraction. 
“It will be observed that the branchiae are placed in the 
course of the current of blood which is returning to the heart, 
which is the exact contrary of what happens in fishes in which 
the blood is sent from the heart to the branchiae on its way to 
the body. It follows, from this arrangement, that the blood 
which goes to the branchiae is blood in which the quantity of 
oxygen has undergone a diminution, and that of carbonic acid 
an increase, as compared with the blood in the heart itself. 
The blood, therefore, which reaches the branchiae has 
lost oxygen and gained carbonic acid; and these organs consti¬ 
tute the apparatus for the elimination of the injurious gas from 
the economy on the one hand, and, on the other, for the taking 
in of a new supply of the needful ‘vital air,’ as the old chemists 
called it. It is thus that the branchiae subserve the respiratory 
function. ” 
METHOD OF STUDY. 
The heart may be fixed in situ by removing a small portion of 
the carapace immediately over it, and then plunging the still 
living animal into strong (95 per cent.) alcohol, hot saturated 
aqueous solution of corrosive sublimate, or 10 per cent, nitric 
acid. By either of these methods the firm carapace prevents 
2 I shall, however, in the present paper use the term heart in its usual 
significance. 
