686 SUMMARY OF CURRENT RESEARCHES RELATING TO 



whilst he objects that these chambers cannot be closed on all 

 sides. This is the kernel of the dispute, everything else is unim- 

 portant. Dr. Flogel objects to Dr. Miiller's experiments in flooding 

 the walls of the diatoms with fluids of different densities, on the 

 ground that " all the fluids named by him will penetrate the inter- 

 stitial molecules of thin membranes with the greatest facility " ; from 

 this assertion Miiller dissents as regards the silicified cell-walls of 

 diatoms, while pointing out the ambiguity of the term " interstitial 

 molecules." He objects also to Dr. Flogel's application of the term 

 endosmose to processes which have not the slightest connection with 

 diosmose, e. g. to the passage of fluid through a porous membrane 

 which is bounded on the other side by air. The fact of the rapid 

 filling up of the chambers and their emptying by evaporation is, 

 according to Dr. Miiller, explained in the simplest manner, if the 

 structure of the cell-wall of Pleurosigma is regarded as analogous to 

 that of Triceratium in this respect, that every chamber is in free 

 communication with the air. This analogy might be carried further, 

 and the author is inclined to assume a double communication, on one 

 side with the outer air or water, on the other side with the cell- 

 cavity. In Triceratium this double connection can be proved — out- 

 wardly a large circular opening, towards the cell-cavity a number of 

 visible pores ; it is very doubtful, however, whether the hypothetical 

 openings in Pleurosigma correspond anatomically to those of 

 Triceratium. 



Dr. Miiller considers it most probable that the cell- wall of Pleuro- 

 sigma consists simply of a poly- 

 gonal network of minute thin bands 

 placed at right angles to the sur- 

 face, and more strongly thickened 

 at the angles on both sides, inwards 

 and outwards. Both the inner and 

 outer edges of transverse sections 

 would therefore have a moniliform 

 appearance (see fig. 135). A com- 

 ^y plete separation of the separate 



Diagrammatic representation of " Pearls '' or transverse sections of 

 Pleurosigma. a, chambers ; 6, openings, the thickened angles can scarcely 



be expected, since in that case the 

 section must be thinner than the diameter of the openings. In the 

 general way the projections of the margins of the cut openings which 

 lie somewhat higher or lower must unite the separate " pearls " with 

 one another, which will readily give the impression of closed 

 chambers. 



Van Heurck's Synopsis of the Diatoms of Belgium.* — This 

 magnificent work gives a description of every species of diatom as 

 yet gathered in Belgium. The introduction commences with an 

 account of the structure and life-history of diatoms, including their 



* Van Heurck, H., ' Synopsis des Diatomees de Belgique.' Texte. 235 pp. 

 8vo, Anvers, 1885. 



