41 
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 bladder can in other words support sudden alte- 
rations in pressure on about 4 atm. 
After 2—-2"/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 fact 
that the air-sacs of the lake form are much more rigid and there- 
fore much 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. 
25 Eva så. | =Z (så |gs 
sk — |SS8s eu! så | PBE | påg 
SAS Segr! så tSs$s| mæs 
"le 398 58 | == 23180 n 
W …. KR g za s S A | Å 
se RE SE GØ 
1 76 1 | 1 
RR BE ØER rue | 
2 (viz. | 
pressure of | 
saturated 1,04 38,0 |! 0,026 | 0,959 
Alteration in the vo water | 
lume of the air-sac vapour.) | 
—| from the lake form ——|— 
under sorger res- | 
i 192 0,964 0,40 | 2,53 | 1,035 
ER RAN Re Be 
 Kllertilon in the vo- 
ni of the air-sac of | | 
el ken ED | 1,54 | 1,035 
lated from Krogh, table mm Mn E | nen I ude |) 
X, p. 198 in the same | 
| Way as the former. | | 
) len alterations ve diameter of the air-sac of the lake form were so small 
hat they were inside the limits of errors. Therefore I have calculated 
tie volume of be air-sac as if it was a cylinder with constant diameter. 
