234 Aquatic Respiration in Soft-shelled Turtles.  {[March, 
But neither the time the turtles remain under water, the filling 
and emptying of the mouth and pharynx, with water, nor even 
the structure of the parts, proves that aquatic respiration occurs. 
Final proof of this is only obtained by comparing the free gases 
found in water with those found in water from the same source alter 
a turtle had been submerged in it without access to air. Water 
so tested showed in one case that a turtle weighing one kilogram 
in ten hours removed from the water seventy-one milligrams of 
free oxygen and added to it 318 milligrams of carbon dioxide, 
Several other determinations were of the same conclusive char- 
acter. 
This indicates a respiration for the same body weight of about 
one twentieth of that occurring in man. 
As indicated by the figures given above, the carbon dioxide is 
greatly in excess of what could be accounted for by the free 
oxygen taken from the water. There are two sources from which 
the extra oxygen might be derived: (a) From the so-called intra- 
Agassiz, in Part 11 of the Contribution to North American Zodlogy, p. 284, sa 
“ Before reading this paper [Dr. Sager’s] we had noticed these organs [processes a 
the pharynx]; but after seeing this turtle [Aspidonectes] remaining under water for 
full half an hour without showing the least sign of oppression, it seems plausible to 
assume that these fringes may be similar to the internal gills of tadpoles, not only in 
their shape but also in their function. There exists, moreover, an extensive network 
of beautiful vessels spreading in elegant dendritic ramifications upon the whole 
lower surface of the Trionycidze which can hardly have another function than that of 
assisting in the process of breathing, as they are too numerous and too large to be 
considered simply as nutritive vessels of the skin. This is the more probable as 
these vessels are very superficial and are only covered by a very thin epidermis. 
They are indeed as plainly visible through the e s = protects them as 
the vessels of any special external breathing organ. 
‘The following table shows the results of three analyses. In the first column is 
the total amount of free oxygen taken from the water (ten liters) in ten hours 
by a turtle weighing one kilogram. The second column contains the quantity of 
tains the actual amount of carbon dioxide added to the water by the turtle, the ex- 
cess of which, over the amount that could be formed from the oxygen taken from the 
water, is given in the fourth column : : 
k 0. | C0. | Actual CO, Excess COy 
Juy Iisssses 71mg. 97 53mg. | 231 mg. 133 3-8 mg. 
oe sa go 44 $ 212.7 “ 1687 “ 
aes soco] 39 5353 168.7 “ 15s 
Ss _ The determinations were made with the greatest care and accuracy by Profes- 
sors Rich and Holton in the chemical laboratory of Cornell University. 
