Oxygen Consumption in Crustaceans — VAN Weel et al. 
215 
which is probably not the result of a sudden 
increase of the rhythm of the beat of the 
scaphognathites or pleopods, because such a 
sudden increase was never observed. On the 
contrary, at low oxygen tensions these struc- 
tures very often beat quite irregularly, but 
apparently more slowly. This means, there- 
fore, that oxygen is no longer the limiting 
factor in oxygen consumption. The fact that 
the amount of available oxygen decreases 
whereas its utilization increases and the water 
propelling mechanisms do not show a sudden 
acceleration can have but one meaning: more 
oxidizable substances become available for 
(direct) oxidation. This must be the result 
Fig. 3. Oxygen utilization in Calappa hepatica. Ab- 
scissa-cubic centimeters of oxygen per liter of water; 
ordinate — percentage of oxygen consumed from the 
oxygen available. 
of a change in metabolic processes which 
produce such readily oxidizable substances. 
Such a metabolic mechanism must be con- 
sidered an important "safety measure" to the 
animals, as they can now maintain life under 
conditions which would probably prove fatal 
without it. However, it does not actually 
change the animal from an "adjustment" into 
a "regulation" type, as the total oxygen con- 
sumption continues decreasing with the oxy- 
gen content of the water. A moment will 
come at which the amount of oxidizable sub- 
stances set free in the tissues is no longer 
sufficient to maintain life with the available 
oxygen. Then the utilization curve will de- 
Fig. 4. Oxygen utilization in Pseudosquilla ciliata. 
Abscissa — cubic centimeters of oxygen per liter of 
water; ordinate-percentage of oxygen consumed from 
the oxygen available. 
crease sharply (Figs. 1-7), and death will be 
the result in a comparatively short time. At 
the relatively high temperatures encountered 
in Hawaii, the crabs usually die in 1 to 2 
hours when the water contains less than 0.96 
cc. O 2 /I., but they stay alive for at least 3 
hours when 1.4 cc. O 2 /I. is present. At lower 
temperatures, wherein the metabolism is at 
a much lower level, they seem to withstand 
lower oxygen tensions successfully. Jordan 
and Guittart (1938) reported, for instance, 
that at 13°C. Potamohius fluviatilis lived for 2.5 
hours in water containing only 0.35 cc. O 2 /I., 
after which period the experiment was ter- 
minated. 
The suggestion that certain substances used 
in respiration are liberated by the tissues, by 
Fig. 5. Oxygen utilization in Phymodius ungulatus. 
Abscissa— cubic centimeters of oxygen per liter of 
water; ordinate — percentage of oxygen consumed from 
the oxygen available. 
