HABITS OF YELLOW PERCH. 325 
in the stagnant water was considerably less than that of those observed simultaneously 
in a cage in the open lake. But the water from 13.5 m. was cool (15° C.), and it would 
therefore be expected that the perch would respire at a slower rate than when in surface 
water (21.6° C.). In order to determine the normal rate of respiratory movements at 
different temperatures two healthy perch were observed in the laboratory on November 
29, and the results are summarized as follows: 
Menipetatire (degrees/cetitigrade):. [050.100 /SCa 2 Ck AREA Aas ee 8 16 
PA GIMET MADER ICE Lem cee ace Matai. sie ros oan wae hin smth ene labiensone spear nena shaS 24.1 38. 5 
20 
45-6 
25 
59°3 
The data indicate that the rapidity of the respiratory movements of the fish placed 
in stagnant water was not materially increased or decreased by such treatment. 
Fro. 32.—Collecting tube and method of collecting gas from perch swim bladders. j, jar full of stagnant water continually 
pumped from depths of lake; m, small vessel for collecting mercury; ?, collecting tube filled with mercury. 
‘The experiments described show that perch in Lake Mendota commonly enter the 
stagnant water below the thermocline and that they may remain there for an hour or 
two without suffocating. These facts suggested that perch might make use of the 
oxygen in the swim bladder while in the stagnant areas, and experiments were performed 
which showed the supposition to be correct. From August 23 to September 24, 1916, 
fishes were lowered in wire cages to depths varying from 12 to 13.5 m. The amount of 
