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On the Microscopical Structure of the Diatom Valve. 



By Julien Deby, F.R.M.S. 

 (Read May 28th, 1886.) 



I have lately been carefully studying the minute structure of the 

 Diatom valve, with a view, if possible, of reconciling the various 

 conflicting opinions entertained on this difficult subject by some of 

 the best living microscopists, and although my researches are still 

 incomplete, I have reached the conclusion that many fallacies are 

 being propagated regarding the Diatom cell-wall, especially in 

 connection with the existence or non-existence of orifices or per- 

 forations of the Valve. 



My belief is that the outer shell of the frustule of the living 

 form is the perfect homologue of the ordinary cell-wall of other 

 plants, and that it is impervious, i.e., free from visible openings, 

 while the so-called " secondary valves," the " Regenerationshiille " 

 of A. Smidt, are homologous with the scalariform and similar 

 thickenings observed in many vegetable cells and vessels formed 

 by these. Although I must reserve for a future occasion a com- 

 plete and elaborate account of my observations, I will lay before 

 the Club a few of my methods of investigation, and some of my 

 principal results. 



I. 



I have had recourse, in the first place, to the method of thin 

 sections of Messrs. Prinz and Van Ermengem. The difference 

 between their conclusions and my own I attribute to the fact of 

 my having almost invariably employed recent diatoms for my in- 

 vestigations, whereas these gentlemen made use of fossil shells, 

 the external films of which had disappeared either by abrasion or 

 by slow chemical action. Messrs. Prinz and Van Ermengem 

 truly represented what they saw, namely, a sieve-like membrane, 

 showing real orifices, but this in the living frustule does not, 

 according to my views, exist. 



I have used as imbedding media, chloride of zinc or chloride 

 of magnesia, mixed with their respective oxides, an idea which 

 was given to me by Mr. Hartmann, formerly of Swansea. As soon 



