xlvi Journal of Proceedings.
" The water contained a considerable number of Rotifers, mostly of the
species I took to be Pleurotrocha gibba, and a few Rotifer vulgaris.
" In a specimen of Vaucheria dillwyni, Ag., gathered from a damp cart-
rut on March 15th, I found a few capsules similar to those described also
containing Rotifers, having the same appearance as those found in the
pond. On placing the plant in water I found it on the following morning
discharging motile spores from the extremity of its threads, a character
common probably to all the species of Vaucheria, Now the question that
puzzled me extremely was, how did the Rotifers gain admission into the
vigorous green Alga? and what gave rise to the remarkably large capsules
Fig. 2.—The Rotifer Parasite on Vaucheria *
invariably tenanted by these creatures ? Is it possible that the Vaucheria
is selected as a favourable nidus, and the abnormal growth produced by
some stimulating action on the same principle as Cynips occasions the
galls on the oak-leaf ? though in this case it would be impossible for the
large eggs to be inserted into the plant, not to mention the fact that the
eggs are apparently all produced by the animal after its inclosure in
the capsule; for I should mention that in the youngest capsules the
creature is much more slender in form than it afterwards becomes, and
the eggs are quite rudimentary. If the plant is really selected as a fit
* The Club is indebted to Mr. Lister's kindness for this cut, engraved by Messrs. West,
Newman & Co., from his own drawings.—Ed.