Larva of Chaoborus Crystallinus (de Geer). 
361 
main tracheal tubes, and we can only suggest the movement is due 
to a flow of the gelatinous coat of the disappearing air sacs along 
the tracheal tubes. Some of the spots, however, are scattered about 
on the sides of the pupa. 
There is a generous supply of tracheae from the thoracic pair of 
sacs ; also a pair of banana-shaped air tubes arise, which appear 
before the collapse of the sacs. (PI. JCVII., fig. 28.) These remain 
tucked away under the integument on the ventral side of the front 
of the thorax, awaiting the completion of the change, when, with the 
slipping of the larval integument, and the adjustment from the 
horizontal position of the larva to the vertical position of the pupa, 
they come into play, taking in atmospheric air, but not until the 
trachea and air tubes have been first cleared by air discharged 
from the larval sacs. 
On one occasion we secured a newly-changed larva before it, as 
a pupa, had an opportunity of reaching the surface to take in 
atmospheric air. We confined it under water, and kept it from 
rising to the surface for four days. It was very active during that 
period, and when we examined it we found the head end was 
darkening, the legs and wings well developed, also the hairs on them. 
There was no air in the trachea of the anal fins. These changes 
developed on the air supply carried over from the sacs of the larva. 
Unfortunately, when removing it on the fourth day from the 
microscope to the tank, it was crushed. With regard to the 
question of respiration, we have here a problem full of puzzling 
•conditions. Krogh has carried out some exceedingly interesting 
experiments to demonstrate the diffusion of the gases through 
the integument of the larva, maintaining that this latter acts as 
one large spiracle. Prof. Miall (f) also suggested that this might 
be a possible method of respiration. 
Krogh proceeds to demonstrate that the gases in the air 
bladder come into diffusion equilibrium with any gas mixtures 
dissolved in the surrounding water, and, consequently, in the 
fluids of the animals. We give the results of his experiments 
as under : — 
He placed a number of larvse for a few hours in different 
bottles, with water saturated with : — 
1. 55 p.c. oxygen and 5 p.c. nitrogen. 
2. 51*5 p.c. oxygen and 48*5 p.c. nitrogen. 
3. Air with 17*8 p.c. C0 2 . 
4. Air with 9 • 5 p.c. C0 2 . 
And found by analysis of the air from the bladders in bottle : — 
1. 91*5 p.c. and 8 '3 p.c. N 2 . 
2. 48*0 p.c. 0 2 and 51*8 p.c. N 2 . 
3. 8*9 p.c. to 6*7 p.c. C0 2 (analysis of two animals). 
4. 5 p.c. C0 2 . 
