The Structure of Diatoms. By Dr. J. II. L. Flogel. 515 



by Schumann's method ; it is therefore unnecessary to enter into 

 the details of his statements. A considerable retrocession is found 

 in Pfitzer's works of 1863 and 1871 (18 and 19). In the former 

 is briefly indicated that in Pinnularia we had to deal with smooth, 

 narrow, elhptical spaces, concave outwards (pores = costee, Smith). 

 In his second he substantiates this view by details. His views 

 do not require special refutation ; they are wholly wrong. 



In my lecture (7) I first gave a correct representation of the 

 real details, with preparations. It seems a pity that this lecture, 

 referred to by Pfitzer (1873) in Just's ' Jahresbericht ' (11, p. 28), 

 did not give him occasion to make once more transverse sections 

 of Pinnularia, for in all probability he would have been luckier. 

 The most recent paper, however, which has come to my knowledge 

 is a notice by Prof. Hallier, April 1882 (10, p. 136), according to 

 which he holds a similar view with regard to the structure 

 of the silicified membrane of Cymhella as Pfitzer expounded for 

 Pinnularia. If this can be looked upon as a confirmation for 

 Pinnularia, then I do not envy Prof. Pfitzer's new triumph, which 

 places Hallier 's reputation in an unfavourable light. 



Among the supporters of this unfortunate furrow-hypothesis 

 seems to be Borscow. whose work I have not seen {vide Pfitzer, 

 Just's ' Jahresb.,' 1873, p. 28). 



The hterature as to the supposed perforation of the cell-wall 

 along the middle line has been given above. I need only add 

 that Pfitzer (19, pp. 175-80) has tried to dispose of Dippel's 

 objections to Schultze, and seems to have succeeded tolerably well 

 in his so-called proof of the longitudinal cleft. But when he states 

 that, in explaining the apparent movements, Dippel has put by far 

 too great weight on the endosmotic processes, this objection falls 

 to the ground, since Prof. Engelmann (4) has discovered a means 

 in Bacteria to demonstrate the development of oxygen by diatoms 

 under the Microscope, thereby furnishing the proof that the unseen 

 gas-molecules escaping from the cell cause movement. Be this 

 attraction or not of the Bacteria, these currents of gas, like enter- 

 ing or flowing currents of water, must have such force that they 

 can carry away a detached cell. 



2. Navicula. 



Of the numerous species, I have only examined the coarser 

 striped Navicula lyra, Ehrb. The material was obtained from 

 the mud gathered during the expedition of the " Pomerania " (9). I 

 chose a serial slide, on which were placed twenty-seven transverse 

 sections through one valve. The lengths of the first and last sec- 

 tions led me to suppose that three or four sections had already been 

 made from the valve at either end, and by mischance are not on 



