Wallich,, on Siliceous Orgayiisms. 
41 
of alternately opening .and closing ; for either of wliich con- 
ditions there does not appear to exist a shadow of proof or 
even probability. 
I would here mention having, very recently, been enabled 
to trace the circulation, most distinctly, in frustules of Pleu- 
rosigma angulatuniy kindly sent me in a living state by Mr. 
Harrison, of Hull. The current invariably flows in one di- 
rection. At the hyaline extremity of the frustules of this 
species the course of the minute granules, carried round by 
the protoplasmic current within, was most palpable. It is 
precisely similar in character to the circulation in Closterium ; 
the granules, however, being much smaller, and the current 
being uninterrupted by the presence of the terminal vesicles 
of the desmidiacean form. The course of the circulation, in 
the immediate vicinity of the terminal nodules, never varied 
during the change of direction of the frustule ; thereby afford- 
ing the most convincing proof that no alternate endosmotic 
and exosmotic action could be influencing its movements. 
Again, if we refer to the experiment made by the author 
of the ^ Synopsis,^ to test the presence or absence of any ex- 
ternal ciliary apparatus in the Diatomacese,"^ we find that the 
colouring particles of carmine and indigo exhibited no trace 
of the currents, which must have been recognisable had ciliary 
apparatus been in operation. And yet it does not appear to 
have occurred to the acute writer in question, that as such 
currents, no matter how produced, are easy of detection under 
the microscope, they ought, by a parity of reasoning, to have 
made themselves manifest from the action of the minute jet 
of fluid adduced as the result of the assumed endosmotic and 
exosmotic action ; or, to put the case still more forcibly — it 
must be evident that a jet of fluid, determined by the alternate 
operation of endosmotic and exosmotic action, at each terminal 
aperture of the frustule (granting the existence of such action 
for argument's sake), of sufficient energy to propel it along, 
must of necessity have been more than sufficient to cause the 
dispersion of such extremely minute bodies as the particles of 
carmine or indigo employed. The test adduced to disprove 
the existence of ciliary apparatus, becomes, therefore, con- 
clusive also against the theory it was intended to support. 
In the case of elongated prehensile filaments, on the other 
hand, currents could not be produced. In some of the 
Monadin(B, and in Peranema, we may observe the kind of 
filament pointed to, and that it serves to propel the creature, 
and perform its office, without giving rise to any current 
* ' Synopsis Brit. Diatom./ vol. i, Iiitrod., p. 23. 
