VI. DESERT ARTHROPODS
3 2 9
Midgut
Other ions
K + water
Malpighian tubule
Rectum
Water
K
Other ions
Hypo- or hyperosmotic fluid
Fig. 7. Diagram of the water and salt circulation in the excretory system of
an insect. From Stobbart and Shaw (1964).
by the overall osmotic concentration, at least in isolated preparations. But
the tubule itself has never been shown to act as an ionic regulator (Maddrell, 1969), neither does it form hypertonic urine [except, perhaps, in
the cryptonephric system of the mealworm described by Ramsay (1964),
TABLE IV
IONIC CONCENTRATIONS OF LOCUST F L U I D S
0
Fluid
Ionic concentration (mean values in mEq/liter)
Na
K
Cl
Saline for drinking
Hemolymph
With water to drink
With saline to drink
Rectal fluid
With water to drink
With saline to drink
300
150
450
108
158
1
405
11
19
22
241
115
163
5
569
° If desert locusts are given strong saline to drink, ionic concentrations in their
hemolymph rise, but not to the level of the saline. Ionic concentrations in their rectal
fluid become higher than those in the saline. From Phillips (1964).