203 



January 18, 1855. 

 Sir BENJAMIN BRODIE, Bart., in the Chair. 



The following communications were read : 



I. " Note to a paper read before the Royal Society on the llth 

 of May, 1854." By J. W. GRIFFITH, M.D., F.L.S. Com- 

 municated by ARTHUR HENFREY, Esq. Received Decem- 

 ber 13, 1854. 



In the paper referred to above, it was stated that the markings or 

 dots upon the valves of the Diatomaceae, are the optical expressions 

 of depressions existing upon the valves. 



All those authors who have paid special attention to the Diato- 

 maceae, have considered the markings to denote cells ; among these 

 we find Ehrenberg*. Kvitzingf, RalfsJ, Smith, and Quekett||. 



The evidence I adduced in regard to the more coarsely marked 

 Diatomacese, as Isthmia, &c., being furnished with depressions and 

 not cells, is, I believe, satisfactory and conclusive ; and this view 

 has been admitted in a paper since read before the Royal Society^. 



A different view has been taken of the nature of the finer mark- 

 ings, as those upon some species of Gyrosigma, by the author of the 

 paper last quoted, as by previous authors ; and the object of this 

 note is to direct attention to the support which the extended view 

 argued for by me in the paper above referred to, viz. that the finer 

 markings also correspond to depressions, derives from analogy. 



The structure of the Diatomacese, and their modes of reproduc- 



* Die Infusionsthierchen. f Die Bacillarien, and Spec. Algarum. 



J Annals of Nat. History, 1843. British Diatomaceae. 



|| Histological Catalogue of the College of Surgeons ; and Lectures delivered 

 before the College of Surgeons. 



H Proceedings of the Royal Society, June 15, 1854. 



