ill!Ill

TERATOLOGY OF DIATOMS. *3
It thus happens that on certain diatoms very singular filamentous
parasites are occasionally found, which are thought to be algae. The
Nitzschia especially are frequently attacked in this way, and in the Atlas
to my Synopsis (pi. 7, fig. 22) will be found a representation of a
Nitzschia a?ignstata infested in this way.
Recently Mr. Grenfell (') has noticed various disciform diatoms having
radiant filamentous appendices, which are very long, excessively thin, and
fairly numerous. Every specimen of his gathering
(fig. 21).
was in this condition
I have also personally established the existence of similar
radiant appendices on the Coscinodiscus excentricus from a gathering
made at Sheerness-on-Sea.
Fig. 2i. Diatoms with filamentous appendices.
The important question in all these cases is whether the appendices
are true parasites or whether they are actually produced by the
frustule ;
it is to be hoped that this problem will be solved by sub-
sequent research. It is advisable in every case to draw attention to
these appendices, as they are only to be seen with difficulty, and can
only be seen to advantage when the living frustules are placed upon a
slide and there allowed to dry of their own accord, the drop of liquid not
being covered over with a cover-glass.
It would be well to try the effect of analine stains on gatherings in a
living state to see whether these productions are not more frequent than
is at present believed.
(') On the occurrence of pseudopodia in the Diatomaceous genera Melosira and Cyclotella,
by J. G. Grenfell, Q.J.M.S., 1891.