540 NATURAL SCIENCE. %'^- 



raphe in the form of fine threads. Then the movement of diatoms , 

 would have a great resemblance to that of Desmidiaceae, which, 

 according to the investigations of Klebs, similarly move with the help 

 of secreted threads of mucus." 



The threads would be completely invisible, owing to their trans- 

 parency and similar refrangibility to the surrounding water, if it were 

 not for the peculiarity of ink granules sticking to them, and it was 

 not found possible to colour them with methyl blue, Congo red, or 

 other aniline stains. Sometimes, however, the adhesiveness appears 

 to be wanting, since frequently nothing could be seen of the threads 

 in actively motile specimens, and the same was the case in a series 

 of other diatoms examined, 5.^., various Navicula species, &c. Perhaps, 

 in these cases, the secreted jelly dissolves quickly again, and the 

 formation of the threads observed in PinmUavia is suppressed. 



The invisibility of the jelly, without application of special 

 methods, is further shown by the fact that, in the investigation in 

 Indian ink of P. nobilis and other species of the genus, it could be 

 demonstrated that these forms are, as a rule, covered with a more or 

 less considerable coat of jelly. It is only recognisable by the fact 

 that the Indian ink does not penetrate the region of the jelly 

 envelope, and even with the application of this method no sharp 

 boundaries to the envelope could be determined with the strongest 

 magnifications. In the motile specimens it could at least be seen 

 that the jelly was interrupted at the nodes on the sides of the shell, 

 so that no hindrance was opposed to the exit of the thread. The 

 anterior current of ink granules takes its course to the nodal point of 

 the raphe along the outside of the jelly envelope, as a result of which 

 it always remains at a definite distance from the surface, as shown in 

 the figure, and first sinks into the raphe at the nodal points. From 

 the presence of this envelope the question might arise whether the 

 supposed jelly thread is not really a thread-like tract of jelly which 

 passes along the surface of the shell, and first becomes free posteriorly, 

 but the authors believe this is not the case. 



Finally, the authors promise us a continuation of these observa- 

 tions, to which all interested in microscopic animal and plant life will 

 eagerly look forward. 



In these researches we have an entirely new light thrown upon 

 what has always been so great a puzzle, the movements of Diatoms, 

 and it is obvious that any form of pseudopodia is quite unnecessary 

 and inadequate to explain it, thus quite justifying the words of Mr. 

 Jabez Hogg quoted at the commencement of this article. 



E. A. MiNCHIN. 



