412 NATURAL SCIENCE {December 
regard these movements as due to a copious production of adhesive 
jelly ejected rapidly and with a certain force from the nodes of the 
frustule. Whether the extremity of the gelatinous thread struck 
the substratum on which the diatom rested or only encountered the 
resistance of the water, the effect would be the same, viz., to drive 
the cell in the opposite direction. 
In opposition to this view O. Miiller explained the phenomena 
as caused by a stream of cytoplasm propelled through the anterior 
terminal nodes into the external cleft of the raphe (which, it will be 
remembered, he supposed to be closed by a median lamina), and 
there moved towards the centre, flowing back into the interior of 
the cell through the canal of the central node. The stream, pro- 
jecting laterally from the cleft, swept with it the suspended granules 
in the neighbouring layer of water, bearing them towards the narrow 
central canal. Here a congestion and accumulation of the cytoplasm 
would occur and, as the effect of the stream on the granules ceased, 
the latter would collect more or less, become agglutinated by the 
dammed-up protoplasm, and subsequently displaced backwards. So, 
according to Miiller, the thread originated, and as the cytoplasmic 
stream moved intermittently, the thread would likewise elongate 
intermittently, and appear as if ejected from the canal of the central 
node. ‘The essential feature of Miiller’s hypothesis lies in the view 
that the material extruded from the interior of the cell is true 
protoplasm ; a view he still maintains in a later communication 
noticed in a postscript to Lauterborn’s work. 
Lauterborn argues at great length against the validity of such a 
conclusion, pointing out first of all that the invisibility of the ex- 
truded material under ordinary conditions militates against the 
protoplasmic theory, since streaming protoplasm is always recog- 
nisable as such without difficulty. It is true that Miiller cited 
Schultze in support of the contention that under certain circum- 
stances the presence of true plasma-streams might escape detection, 
but in the special cases mentioned by Schultze (Gromia, Diflugia) 
the contour of the pseudopodia was always clearly defined. Further, 
it is necessary to remember that protoplasm, which when Schultze 
wrote (1865) might be described as ‘ hyaline’ or ‘ structureless,’ is 
so no longer, thanks to improved optical appliances, and there is no 
ground for supposing that, in cases where granules are moved along 
by the pseudopodia of rhizopods, the protoplasm ever resembles the 
streaming substance in Pinnularia. Lauterborn also lays stress 
upon the fact that the collections of cytoplasm normally occurring 
at the poles of the Pinnularia cell exhibit a beautifully defined 
reticular structure during life, and that it is in these regions that 
Miiller’s streams of cytoplasm originate. To imagine that the 
cytoplasm is completely changed in passing through the polar cleft 
