244, WILLIAM HATCHETT JACKSON. 
obtained by myself from the same sponge, form the subject- 
matter of the present paper. 
This Infusorian belongs to a remarkably mteresting type, 
and appears to be a genus altogether new and hitherto un- 
described. It was happily in my power to make a very 
complete and prolonged examination of structural details in 
many specimens ; the results thus acquired I will now pro- 
ceed to state as fully as possible, and then say a few words 
on the affinities and position of this organism. 
All the examples found by Mr. Poole and myself were 
obtained by tearing up small portions of sponge on a glass 
shide and then hunting about among the fragments under a 
microscope. When a fresh-water sponge is broken across, 
the internal substance is seen to be of a whitish hue and 
surrounded by an outer (cortical) green layer. From this 
green layer came all my specimens. None could be obtained 
from the water in which the sponge lay, though portions 
were repeatedly taken up by a pipette close to the sponge 
itself and from other parts of the can in which we kept it. 
Hence it seems that our Infusorian may justly be regarded 
as ecto-parasitic, probably living on the surface or in the 
more superficial layers of the sponge substance. 
As to size, the animal is quite invisible to the naked eye, 
but may easily be made out with a No. 4 object glass and 
ocular 2 (Hartnack). The figures on Pl. XII were drawn 
under a No. 8 object glass with ocular 2 quadrillé, the details 
being further worked out under the same object glass with 
ocular 4 and the tube drawn out. The body measures from 
71, to ;4, of aninch in transverse diameter ; while from the 
tips of the cilia on the one side to those on the other the 
measurements varied from z2, to ~3, of an inch. 
As seen when slowly moving on the under surface of the 
thin cover-glass it shows a central disc fringed externally by 
a circle of cilia—a striated border and a peculiar apparatus 
of hooks borne by a ring composed of a substance altogether 
different from the rest of the animal, supported by processes 
running inwards towards the centre of the disc. This centre 
is a deep cup-shaped hollow, limited by a hyaline -wall 
through which are visible granules, vacuoles, nucleus, and 
ciliated pharynx. The basal portion of the ciliary fringe 
is partially obscured by a clear border with a few granules 
init. This view is represented in fig. 1. But when the 
animal quits the cover-glass and swims, as it does very 
rapidly, to a piece of sponge-substance, the side view has 
the appearance shown in fig. 2. This is the natural posi- 
tion when swimming, the animal invariably moving with the 
