So, too, I found that Radiolarians were killed by a day's
exposure to sunshine, even in cool water, and it is to the need for
escaping this too rapid oxidation that I ascribe their remarkable habit
of leaving the surface and sinking into deep water early in the day.
It is easy, too, to obtain direct proof of this absorption of a great
part of the evolved oxygen by the animal tissues through which it has to
pass. The gas evolved by a green alga (_Ulva_) in sunlight may contain
as much as 70 per cent. of oxygen, that evolved by brown algae
(_Haliseris_) 45 per cent., that from diatoms about 42 per cent.; that,
however, obtained from the animals containing _Philozoon_ yielded a very
much lower percentage of oxygen, e.g. _Velella_ 24 per cent., white
_Gorgonia_ 24 per cent., _Ceriactis_ 21 per cent., while Anthea, which
contains most algae, gave from 32 to 38 per cent. This difference is
naturally to be accounted for by the avidity for oxygen of the animal
cells.
Thus, then, for a vegetable cell no more ideal existence can be imagined
than that within the body of an animal cell of sufficient active
vitality to manure it with carbonic acid and nitrogen waste, yet of
sufficient transparency to allow the free entrance of the necessary
light.
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