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SOME NOTES ON THE STRUCTURE OF DIATOMS. 



By N. E. Brown, A.L.S. 

 (Read March 2ith, 1914.) 



Plate 23. 



These notes are offered to the Quekett Microscopical Club, not 

 -with the anticipation that, with the exception of one point, the 

 -expert will find in them much that is not already known, but 

 because my interpretation of certain familiar features is different 

 from that which is usually accepted and may therefore be of 

 some interest in promoting thought in another direction. 



Structure of Pirmuiaria spp. Although P. major and allied 

 species are familiar to all microscopists and their structure is 

 doubtless well understood by experts, yet the description of it in 

 English text-books is by no means satisfactory and also does not 

 seem to be too well known. A good description with figures by 

 Floegel will, however, be found in the Journal of the Royal Micro- 

 scopical Society, 1884, vol. 4, p. 509, t. 8 (Pinnularia). 



I regard P. major as a very simple type, perhaps one of the 

 simplest types of diatom-structure. In front view the valve pre- 

 sents a series of transverse markings on each side of the raphe, 

 which are so easily seen that I believe few diatom- dotters pay much 

 attention to them. These markings consist of linear cavities or 

 canals in the valve, separated from one another by very thin par- 

 titions, and each of them is provided with a comparatively large 

 linear-oblong opening on the inner side, communicating with the 

 interior of the diatom ; it is evident that during life the protoplasm 

 enters and fills these cavities, and therefore they must play an 

 important part in the life-economy of the diatom. The motions of 

 n living diatom are not only interesting to watch, but are puzzling 

 to everv one who has observed them. It is no uncommon thing to 

 see a Pinnularia or other free-swimming diatom apparently take 

 hold of a particle of dirt and move it to and fro along its sides or 

 upper surface. On one occasion I saw P. major with two frag- 

 ments of dirt, one on each side of it near the margin ; both pieces 

 "were moved forwards and backwards in the same direction for 

 -a time and then suddenly they were moved each in a different 



