DIATOM MOTION. IO9 



plasm is universally webby in structure, even in the thinnest 

 extensions of pseudopodia, and appeals to Biitschli's work. * 

 But we find in the second figure of the very first plate of 

 Biitschli's drawings an illustration of two pseudopodia of 

 Gromia apparently structureless, and on the opposing page 

 these are described in set terms as "hyaline." Moreover, 

 even these pseudopodia are not quite of the tenuosity we may 

 reasonably attribute to a film of flowing plasma no thicker 

 than the flagellum of a bacterium. For no thicker than this 

 would be the stream that fills the raphe of a Pinnularia. And 

 even in the somewhat more massive stream within the keel of 

 Siirirella, it would seem unreasonable to look for reticulated 

 structure so long as the substance is in streaming condition, 

 or expect the thin substance to remain ^V^ situ during fixing 

 and staining, and reveal a webbiness that is just barely vis- 

 ible even in the most substantial protoplasm in the ribs. 



And secondly, Lauterborn necessarily bases himself on the 

 visibility in water of living protoplasm, no matter how tenu- 

 ous its form. But even the flagellse of living bacteria, which 

 are much more dense in consistency than streaming plasma, 

 and yet as wide as these currents within the raphe, are at the 

 limit of visibility with ordinary methods of illumination and 

 the best optical aids. Furthermore, recent work at the Uni- 

 versity of Pennsylvania (the published paper is not immedi- 

 ately at hand) has served to show that the more tenuous 

 extensions of rhizopods have been entirely overlooked, but 

 that their existence can be detected, with all conditions favor- 

 able, by an extraordinarily good eye. But these rhizopod 

 extensions are in much better position to be seen than any 

 raphe protoplasm. 



The stream within the raphe of Pimmlaria, and that 

 within the keel of Stirirdla, may alike be protoplasm, clothed 

 indeed with ever-secreting jelly, but still protoplasm. The 

 diatom's protoplasm continually gives off this substance, and 



*Protoplasm and Microscopic Foams. English translation. London, 1894. 



