418 F. R. ROWLEY ON SOME POINTS IN THE STRUCTURE 



In proceeding first of all to deal with the protoplasm and 

 its inclusions, it is hardly necessary to mention that, in Diatoms, 

 the living protoplasmic material is shut in between two valves, 

 one of which fits over the other like the lid upon a pillbox. 

 These valves are encrusted with silica, and when all the organic 

 parts are removed by suitable treatment, we get the Diatom 

 in the familiar guise of the ordinary cabinet specimen. 



The inner structure of Diatoms was first efficiently studied 

 by Pfitzer a little more than thirty years ago. During this 

 interval our knowledge of the structure and life of the cell has 

 undergone an entirely unexpected extension and deepening. 

 Features which are of primary interest in Cytology, such as the 

 structure of protoplasm, the construction of the resting nucleus, 

 and especially the karyokinetic process, had scarcely been studied 

 in the Diatomaceae, and therefore challenged enquiry first 

 of all. 



With regard to the arrangement of the protoplasm in the 

 interior of the cell, Lauterborn was able to confirm in the main 

 Pfitzer's results. In studying inclusions in the protoplasm, special 

 attention was paid to the so-called "red granules" ("roten 

 Kornchen ") first' discovered by Biitschli, with the result that many 

 bodies previously regarded simply as oil drops were shown to 

 belong to that category. 



A very interesting section of Lauterborn's paper is that dealing 

 with the minute structure of the protoplasm. Biitschli had 

 previously pointed out that Surirella was admirably adapted for the 

 study of living protoplasm, and Lauterborn extended his researches 

 to other forms with great success. Under comparatively low 

 powers the protoplasm of Diatoms appears simply finely granular, 

 as described by the earlier observers, but with the aid of the best 

 lenses and under favourable conditions — particularly in cases 

 where the layer of protoplasm is thin and as free as possible 

 from embedded granules — it is often possible to recognise a 

 distinctly reticulated structure, and this, it should be remembered, 

 not merely in preserved material, but in the living cell substance. 

 It may be observed, for instance, in the small masses of proto- 

 plasm which occupy the extremities of the frustule in Pinnularia 



