426 THE MICROSCOPE. 



nomenon -which can be compared with the ghding motion 

 of foreign bodies on the Diatomaceae, and that is, the 

 taking up and casting off of particles by the pseudopodia 

 of the rhizopoda, as observed, for instance, on placing a 

 living Gromia or Miliolina in still water along with 

 powdered carmine. The nature of the adhesion and of 

 the motion is in both cases the same in all respects. And 

 since, with Diatoms as unicellular organisms, protoplasm 

 forms the principal part of the cell body (in many cases 

 two distinctly moving protoplasms), everything suggests 

 that the external movements are referable to the move- 

 ments of this protoplasm." It is quite evident to those 

 who have studied the movements of the Diatoms that 

 they are surrounded by a sarcode structure far more deli- 

 cate in its character than that of the Amoeba. Six years 

 before Schultze's observations were published, the fact 

 appeared in a third edition of tliis work, page 307 ; therein 

 it is stated that "The act of progression rather favours 

 the notion of contractile tentacular filaments, — p^ez^c/o- 

 podia, — as the organs of locomotion and prehension. The 

 hyaline or sarcode covering is of so transparant a nature 

 that as yet no microscopic power has enabled us to assign 

 its precise boundary and attachments.^ Some observers 

 would deny a membranaceous (hyaline) covering of any 

 kind to Diatoms, which we have certainly seen." Pro- 

 fessor Smith, of America, has satisfactorily traced a sar- 

 code covering in Pinnularia. The defining power, pene- 

 tration of the objective, and mode of illumination, is 

 everything in such investigations. 



It was in 1841 Messrs. Harrison and SoUitt, of Hull, 

 discovered the beautiful longitudinal and transverse stricB 

 (groovings) on the Pleurosigma hippocampus. A curved 

 graceful line runs done the shell, in the centre of which is 

 an expanded oval opening. Near to the central opening 



macese, 



a species 



a species at least six times their own size ; " and Mr. Barkas states tliat he ha^ 

 seen tliem "push away particles of foreign matter, and that with the greatest 

 apparent ease, at least one hundred times larger than all the frustules com- 

 bined ; and what is more remarkable still, is that they not only pusli the accu- 

 mulated particles away when they are in their direct line of motion, but, if 

 they merely touch them in p;issing, they drng them after them as though they 

 were literally held by soirje magnetic attraction, or strong cement." 



