The Structure of Diatoms. By Dr. J. H. L. Flogel 681 



** Which are situated on the inner surface of the membrane 

 where the chambers at the same time have the 

 enormous extent of almost half the breadth of a valve. 

 Pinnularia, and probably all single striated forms. 

 h, without distinct openings, but of considerable size. 

 * With quite smooth chamber- walls : 



Coscinocliscus centralis, and others. 

 ** With nodular thickened chamber- walls : 

 Eupodiscus. 

 c, closed on all sides, and extremely small, approaching the 

 limit of discrimination : 



Pleurosigma, Navicula Lyra, Surirella, Achnanthes 

 (the finer marked variety), and probably most of 

 the finely dotted striated forms. 



Having thus given proof of the existence of various types as 

 the cause of the surface-image, the necessity arises of refuting those 

 investigators who constantly talk of a diatom sculpture in general, 

 of surface-sculptures, of furrows, cup-like depressions, hemispherical- 

 shaped prominences, &c. In so far as this has not already been 

 done in my paper 1 now undertake the task. 



Prof. Weiss propounded in 1871 (28) an entirely new view 

 of the sculpture of diatoms, which is formulated by him (pp. 15-6) 

 as follows : " The markings of the various diatom species, however 

 difierent they may appear under low magnification, difier only 

 apparently; under high magnification, and with a correct inter- 

 pretation of the sculpture, all diatoms are constructed on the 

 same principle, namely, they consist of more or less polygonal 

 cellules, the walls of which, with low magnification, produce and 

 condition the configuration of the so-called markings." The inner 

 cavity he compares (p. 9, footnote) with the embryo-sac of the 

 higher plants. The notion that the envelope consists of numerous 

 minute cells is so thoroughly erroneous that we need not quarrel 

 about it. The attributes of a cell do not consist, according to our 

 present knowledge, in the wall alone which surrounds a cavity, 

 and it is impossible to look upon each cavity as a cell-lumen even 

 if it should have regular form. The discovery of nuclei within 

 the so-called cells (p. 30) must be traced back to an error in the 

 examination ; they would never have escaped me in my manifold 

 staining processes. Nuclei which take up no colour I may say 

 do not exist. The idea that all diatoms have a common sculpture, 

 I contradict most emphatically. I cannot at all comprehend how 

 Prof. Weiss, with his great knowledge of details, and with the 

 enormous quantity of material at his disposal, can have arrived at 

 such an opinion. We must, however, give Weiss the credit that 

 he was the first to demonstrate that tJie presence of cavities closed 



Ser. 2.— Vol. IV. 2 Z 



