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 0. Mtiller 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 Mtiller'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, Difflugia) 

 the contour of the pseudopodia was always clearly denned. 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 



