It is now necessary to pass to the discussion of a widely distinct
subject--the long outstanding enigma of the nature and functions of the
"yellow cells" of Radiolarians. These bodies were first so called by
Huxley in his description of _Thallassicolla_, and are small bodies of
distinctly cellular nature, with a cell wall, well defined nucleus,
and protoplasmic contents saturated by a yellow pigment. They multiply
rapidly by transverse division, and are present in almost all
Radiolarians, but in very variable number. Johnnes Muller at first
supposed them to be concerned with reproduction, but afterward gave up
this view. In his famous monograph of the Radiolarians, Haeckel suggests
that they are probably secreting cells or digestive glands in the
simplest form, and compares them to the liver-cells of Amphioxus, and
the "liver-cells" described by Vogt in _Velella_ and _Porpita_. Later
he made the remarkable discovery that starch was present in notable
quantity in these yellow cells, and considered this as confirming his
view that these cells were in some way related to the function of
nutrition. In 1871 a very remarkable contribution to our knowledge of
the Radiolarians was published by Cienkowski, who strongly expressed the
opinion that these yellow cells were parasitic algae, pointing out that
our only evidence of their Radiolarian nature was furnished by their
constant occurrence in most members of the group.
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