mospheres. When the pressure however was augmented to 4,7 — 
4,8 atm., total pressure, (corresponding to the pressure 37 — 38 m. 
below the surface) the larva when not swimming sinks to the bot- 
tom. By examination with lens it was visible that the air-sac had 
kept its normal form and that it was still filled with air. 
The tracheal biadder can in other words support sudden alte¬ 
rations in pressure on about 4 atm. 
After 2 — 2 V 2 hours the larva had attained the equilibrium again. 
The proper mechanism of this compensation had not been exa- 
mined but we can surely conclude that it is of the same nature 
as that of the pond form. 
The result of this investigation is that there seems to be no 
essential difference between the function of the air-sacs of the lake 
form and the pond form. 
The difference which is observed is only caused by the faet 
that the air-sacs of the lake form are mueh more rigid and there- 
fore mueh more resistent against pressure than those of the pond 
form, a circumstance on which the above mentioned anatomical 
and histological facts give a clear explanation. 
Pressure in 
em. mercury 
P- 
d 
£.2^ 0 ^' 
- s II 222 
s £= ^ — o'*' 
nJ > 
Volume of 
an air bubl)le 
Pressure in 
the air-bubble 
pi const. 
Pressure in 
the air-sne 
p 2 coiist. 
1 
76 
1 
1 
1 
1 
2 
Alteration in the vo- / 
lume of the air-sac 
from the lake form < 
under different pres¬ 
sure ^ 
2 (^viz. the 
pressure of 
saturated 
water 
vapour.) 
1,04 
38,0 
0,026 
0,959 
3 
192 
0,964 
0,40 
2,53 
1,035 
4 
Alteration in the vo¬ 
lume of the air-sac of 
the pond form calcu¬ 
lated from Krogh, table 
IX, p. 198 in the same 
way as the former. 
116 
0,964 
0,66 
1,54 
1,035 
h The alterations in diameter of the air-sac of the lake form were so small 
that they were inside the limits of errors. Therefore 1 have calculated 
the volume of the air-sac as if it was a cylinder with constant diameter. 
