ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 103 



poses that the cell of the diatom, which contains a deposit of proto- 

 plasm, sends out processes or laminfe through the pores in the cell- 

 wall, or through the suture which separates the two halves. These 

 processes of the protruding protoplasm (or, it is even said, a thin layer 

 completely enveloping the alga) are considered to produce by their 

 contractility all the phenomena of motion. Schultze and Engelmann 

 have recourse to the following indirect arguments : — 



(1) They maintain that these movements only take place when the 

 algae touch some fixed object with the suture ; * when, on the contrary, 

 they swim free in the water no motion is observed. Without the 

 assumption of an envelope of protoplasm this phenomenon is, in their 

 opinion, quite inconceivable, 



(2) Von Siebold and M. Schultze's observations are adduced, 

 according to which indigo and carmine particles when they touch the 

 suture remain attached to it, and begin to move backwards and for- 

 wards in its direction, just as grains of chlorophyll do in the proto- 

 plasm of the cells of Vallisneria.'\ 



Besides this, the diatom not unfrequently draws after it a cluster 

 of grains of sand, &c., sometimes of very considerable dimensions. 

 This cluster has no connection with the posterior end of the cell, but 

 is at a greater or less distance from it. These authors therefore con- 

 sider that probably an invisible thread of protoplasm connects the 

 cluster with the alga and draws it after it. 



(3) An external layer of protoplasm is said to have been recently 

 discovered, which envelops the threads of Oscillarioe., and produces 

 various motile phenomena. From analogy it may be assumed that the 

 Diatomace^ are also surrounded by a similar external layer ; and this, 

 it is alleged, explains all the phenomena of motion in the Diatomacete, 

 and the more so since they are very similar to those of the OsciUari(E.\ 



Other botanists, such as Naegeli,§ Dippel,|l v. Siebold,^ Kaben- 



* Borscow says, " The movement is quite independent of the relative position 

 of the cells. M. Schultze (1. c, p. 385) is decidedly wrong when he maintains 

 that the cells of Bacillariacese only exhibit movements when they lie on the valve 

 side, where, according to M. Schultze, the raphe or sutm-e is. The best proof of 

 this is furnished by such forms as Cylindrotheca and Nitzschiella, which besides the 

 motion backwards and forwards in the direction of the longitudinal axis of the 

 cell, revolve at the same time round the axis, and consequently must be alter- 

 nately sometimes on the valve surface and sometimes on the hoop surface " 

 (1. c, pp. 35-36). 



t Borscow has besides already pointed out that on touching any other part of 

 the diatom carmine-particles assume a gliding movement. See Borscow, ' Die 

 Siisswasser-Bacillarien des siidwestlichen Russlands,' 1873, p. 36. 



X As regards Engelmann's observations on the layer of protoplasm enveloping 

 the threads of Oscillarise, they seem to the author to be far from satisfactorily 

 proving such an assumption. On applying an induction-current or strong sul- 

 phuric acid Engelmann saw surrounding the whole alga a distinct tliough very 

 fine envelope with a double contour. This envelojoe dissolved in a weak alkaline 

 solution, in hydrochloric acid, and in a 10 per cent, solution of common salt. Our 

 knowledge of the chemistry of mucus products is however as yet too imperfect to 

 allow us to exclude with certainty the idea that the process described was owing 

 to something else than protoplasm (e. g. raucous cellulose). 



§ ' Beitrage zur wiss. Botanik,' 2 Heft, 1860, pp. 90-91. 



II ' Beitrage zur Kenntniss der in den Soolw'assern von Kreuznach lebenden 

 Diatomeen,' 1870, p. 32. 



\ " Ueber einzellige Pflanzen und Thiere," Zeitschr. wiss. Zool., i. (1849) p. 284. 



