I08 PALMER : 



point of his plasma-stream, the main current draws along by 

 adhesion the less vigorous secretions further toward the end. 

 As for any reentering plasma stream at this place, why should 

 it crawl this far over the long, open raphe, to crowd in at an 

 infinitesimal pore against the solid mass of protoplasm there 

 situated? Not even in the raphe itself was protoplasm to be 

 detected by any device. Furthermore, in a case analogous, 

 that of Siin'rella, all the evidence favors the view that the 

 moving stream in the tube of the long keel is secreted jelly, 

 coleoderm substance in short. In Siirirella, indeed, accord- 

 ing to L,auterborn, we have an opportunity to see the actual 

 limit of protoplasm, which stretches up through the ribs of 

 the keel, showing plainly the webby structure made familiar 

 by the studies of Biitschli, but these reticulations stop at the 

 ends of the ribs, and in the keel itself there is nothing of the 

 kind visible. 



The discussion protracted itself with much display of abil- 

 ity on both sides, and ended with these differences of opinion 

 only : The motion of the diatom, according to Miiller, is due 

 alone to the raphe-stream, and the raphe-stream is essentially 

 streaming protoplasm, however covered with coleoderm. 

 According to Lauterborn, the raphe-stream is coleoderm alto- 

 gether, even within the raphe, and the filament into which it 

 finally extends contributes also to push the diatom along. 



So, therefore, we have mechanism enough revealed, and 

 agreed upon, though opinions may vary as to some of the 

 details. It is impossible here to give all the arguments pro 

 and con as to the limits of the protoplasm in the species 

 studied. The honors have been thought to be with L,auter- 

 born in this polemic, and certainly his work has done much 

 toward showing the exact status of the whole question. But 

 with all this granted, one does not quite feel that all has been 

 said, or even that everything has been discovered. 



The Lauterborn view is not, one feels, absolutely convinc- 

 ing. On at least two points there is good chance for questions. 



Lauterborn makes strong assertion to the effect that proto- 



