148 PALMER : 



the keel-canal is full of an altogether hyaline and freely-flow- 

 ing jelly-like substance {ehier durchaus hyalinen sehr fliissig- 

 keitsreichen gallertartigen Substaiiz) which performs the shift- 

 ing of extraneous particles along the keel. Now this shifting 

 of particles along the keel is one of the concomitants of the 

 locomotion of Siirirella, and admittedly due to the operation 

 of the same force that moves the diatom as a whole. The 

 diatom therefore moves, not by the direct action of proto- 

 plasm upon the surroundings, but by the action of a secreted 

 jelly {Gallerte) circulating in the keel and moving back and 

 forth in the keel -cleft (See Figure I, at the right). There is 

 no protoplasm in this keel — such is the contention. 



It would be easy to demand details, and difficult to furnish 

 them, concerning the question as to what causes this '' gallert- 

 artigen Siibstanz'' thus to flow back and forth, and really to 

 function in essential respects like common living protoplasm. 

 But it is to be remembered that Lauterborn, at the time when 

 this was written, was in the midst of a lively controversy 

 concerning protoplasmic limits ; and having somewhat rashly 

 denied the existence of plasma currents even within the raphe 

 of Pimmlaria, he had betaken himself to Siiri^rlla in the 

 search for an argument a fortiori. In place, therefore, of 

 further objections on general lines, let us proceed to some 

 definite observations of fact. 



In my immediate neighborhood a small spring of excep- 

 tionally pure water issues into a basin about three feet across 

 and eighteen inches deep. The pool is well shaded. On the 

 bottom are dark olive patches of diatoms, forming tenacious 

 sheets capable of being lifted nearly free from subjacent sand 

 and loam. These growths consist mainly of millions of 

 Navinda Iridis Ehr. and its varieties, but with them live con- 

 tinuously a few N. Dactylics Ehr., A^ socialis Palmer, and 

 Stirirrlla elega?is Ehr., the last often heavily fringed with 

 Fragilaria parasitica Green. The water is so pure and free 

 from toxin-forming organisms that a thick layer of the dia- 

 toms keeps in good condition in a bottle of it for weeks at a 



