16 SCHULTZE, ON DIATOMACEE. 
Somewhat differently does the granular stream flow on in 
Rhizosolenia. The long, completely transparent, very delicate 
siliceous tubes possess yellow contents, as Brightwell indeed 
saw; and certainly this yellow colour is dependent on 
coloured vesicles of a long oval, nearly rod-shaped figure, 
almost equaling in their long diameter those of Coscinodiscus 
and Denticella. They lie imbedded in a colourless substance, 
containing fine granules, which is again the seat of the 
appearances of currents, in which here, however, departing 
from the Diatoms first described, the coloured vesicles take a 
lively part. A denser opaque accumulation of the granular 
matter and coloured frustules, situated sometimes in the 
middle, at others nearer one end of the tube, in which a 
nucleus, as in Coscinodiscus and Denticella, could not be seen, 
presents itself as the centre of the currents. These do not 
radiate in all directions through the middle of the tube, but 
confine themselves closely from the beginning to the surface 
of the siliceous coat, and run off usually as fine, stretched, 
parallel threads, until, in the pomted end of the tube, they 
unite themselves again to a generally small expanding opaque 
mass. I once counted in the circumference of the tube sixteen 
such granular threads, flowing parallel and beside each other. 
The current is in each of the threads double. Small 
granules, flowing in a more homogeneous substance, some- 
times more quickly, at others more slowly, collect them- 
selves together here into a little mass; they are there seen 
only singly, projecting out on the margin beyond the surface 
of the thread, or apparently entirely imbedded in it. Fre- 
quently one or many of the coloured frustules are laid hold 
of by the current and carried far away to a distance; others 
lie quietly between the streams in a perfectly undisturbed 
layer. Bridge-like joiings, meltings away, and divisions also 
occurred. So much I remember. Alas! more accurate 
notes I did not make. It may be that the phenomenon, for 
that reason, will commend itself to others for further 
research. 
The granular currents described, namely, those in the 
interior of Coscinodiscus and Denticella, entirely resemble 
those known to exist in Noctiluca. In it they proceed from 
a dark mass, which eccentrically took the place on which 
the spherical body possesses a heart-shaped recess, and 
radiate in all directions in the interior of the hollow space of 
the body, which is filled with a clear fluid, passing away into 
an exceedingly fine network of streams immediately under 
and surrounding the skin, and ultimately melting away with 
skin itself, which (if we would transfer an idea from the 
