216 
Fig. 6. Oxygen utilization in Platypodia granulosa. 
Abscissa — cubic centimeters of oxygen per liter of 
water; ordinate — percentage of oxygen consumed from 
the oxygen available. 
some life process, at low oxygen tensions is 
not as hypothetical as it seems to be. Helff 
(1928) has already discussed the possibility 
of oxygen being secreted by the tissues, but 
this idea has been rejected, chiefly because of 
errors in his experimental method (Maloeuf, 
1936). Recently Harnisch (1951), using a bet- 
ter technique, reached the same conclusion 
in his experiments on Chirommus larvae. He 
was able to prove this assumption correct by 
investigating the hemoglobin of the larvae 
spectrophotometrically: at very low oxygen 
tensions the hemoglobin contained more oxy- 
gen than would be possible without such a 
secretion. By observing the living animal con- 
tinuously, he could actually observe the re- 
oxidation of the reduced hemoglobin. When, 
however, the oxygen reserve was consumed 
(probably because of a weakening of the life 
processes necessary to liberate the oxygen, 
which means that the latter was not present 
in reserve as free oxygen), re-oxidation of the 
hemoglobin ceased. Koenen (1951) also men- 
tioned the sudden rise of oxygen consump- 
tion at low oxygen tensions in her experiments. 
The utilization curves of Phymodius and 
Platypodia (Figs. 5, 6) slope down in the be- 
ginning of the experiment. This may be 
caused by an ineffective propelling mechan- 
ism. At 3-3.2 cc.02/h (Phymodius) and 2.9-3. 1 
cc. O 2 /I. [Platypodia), we again get the sudden 
PACIFIC SCIENCE, VoL VIII, April, 1954 
rise of the curve, followed by the now familiar 
decrease at 1.8-2. 2 cc. O 2 /L 
The mud- dweller Podophthalmus, on the 
other hand, shows from the beginning a 
slight increase of the utilization curve (Fig. 
7) which may be due to a more effective 
stroke of the scaphognathites. Some regula- 
tion might be expected in an animal living in 
a habitat that is usually poor in oxygen. Be- 
cause of the adaptation to such a habitat, we 
would also expect the safety measure to occur 
at a lower oxygen tension than in animals 
normally living in much better aerated water. 
The curve shows, indeed, a steep rise at 1.5 
cc. O 2 /I. The final drop seems to occur at 
around 1.3 cc. 02 /h How do these data fit 
into the ecological pattern.^ We cannot expect 
the safety measure to be thrown into gear at 
very low oxygen tensions in Metopograpsus 
(practically an air-breather) , Pseudozius (which 
lives in well-aerated water of the tidal zone), 
or Phymodius and Platypodia (which live on 
corals). Here, due to currents and, during the 
day, to photosynthesis by algae, the water is 
certainly not poor in oxygen. Calappa and 
Pseudosquilla, living on sandy flats in shallow 
water, seem to be in a less favorable situation. 
However, the organic matter present is not 
very abundant (as compared with organic 
mud), and minute algae covering the surface 
will produce during the day a fairly abundant 
Fig. 7. Oxygen utilization in Podophthalmus vigil. 
Abscissa — cubic centimeters of oxygen per liter of 
water; ordinate-— percentage of oxygen consumed from 
the oxygen available. 
