of
oxygen.
At first sight it might seem impossible to reconcile this copious
evolution of oxygen with the completely negative results obtained from
the same animal by so careful an experimenter as Krukenberg, yet the
difficulty is more apparent than real. After considerable difficulty I
was able to obtain a large and beautiful specimen of _Anthea cereus_,
var. _smaragdina_, which is a far more beautiful green than that with
which I had been before operating--the dingy brownish-olive variety,
_plumosa_. The former owes its color to a green pigment diffused chiefly
through the ectoderm, but has comparatively few algae in its endoderm;
while in the latter the pigment is present in much smaller quantity;
but the endoderm cells are crowded by algae. An ordinary specimen of
_plumosa_ was also taken, and the two were placed in similar vessels
side by side, and exposed to full sunshine; by afternoon the specimen of
_plumosa_ had yielded gas enough for an analysis, while the larger and
finer _smaragdina_ had scarcely produced a bubble. Two varieties of
_Ceriactis aurantiaca_, one with, the other without, yellow cells, were
next exposed, with a precisely similar result.
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