VI. DESERT ARTHROPODS
335
Fig. 10. (a) Diagram showing the cryptonephric system of adult Tenebrio
molitor, the mealworm beetle. Three of the six Malpighian tubules are shown,
enclosed in the perinephric membrane. The number of convolutions of the
tubules and of the boursoflures has been reduced, (b) Diagram of the rectal complex as seen in a transverse section through the posterior region. From Grimstone
et al (1968).
indeed Grimstone et al. (1968) believe that the posterior part of the rectum contains air from which water vapor is absorbed by the rectal cells
as water is evaporated into it from the fecal pellets. A relative humidity
of 90% is theoretically equivalent to an osmotic pressure of 140 atm, so
that the osmotic work of the rectal cells is indeed reduced by the presence
of a perirectal fluid with an osmotic pressure of something like Δ 8°C.
We shall refer to these matters again below under "water vapor
absorption."
Most of the information so far available about water balance in relation
to excretion has been derived from nondesert insects (Calliphora and Perl·
planeta) but it is very relevant to the present enquiry. Investigation of
335
Fig. 10. (a) Diagram showing the cryptonephric system of adult Tenebrio
molitor, the mealworm beetle. Three of the six Malpighian tubules are shown,
enclosed in the perinephric membrane. The number of convolutions of the
tubules and of the boursoflures has been reduced, (b) Diagram of the rectal complex as seen in a transverse section through the posterior region. From Grimstone
et al (1968).
indeed Grimstone et al. (1968) believe that the posterior part of the rectum contains air from which water vapor is absorbed by the rectal cells
as water is evaporated into it from the fecal pellets. A relative humidity
of 90% is theoretically equivalent to an osmotic pressure of 140 atm, so
that the osmotic work of the rectal cells is indeed reduced by the presence
of a perirectal fluid with an osmotic pressure of something like Δ 8°C.
We shall refer to these matters again below under "water vapor
absorption."
Most of the information so far available about water balance in relation
to excretion has been derived from nondesert insects (Calliphora and Perl·
planeta) but it is very relevant to the present enquiry. Investigation of