12 THE STRUCTURE AND LIFE 



either side, a second current, which returns by the polar cleft of the 

 posterior nodule. In this case the motive forces act in the same direction, 

 and the cell moves forward in a direction opposite to the current. 



If, on the other hand, the currents issue at the same time from the polar 

 clefts towards the openings of the central nodule, then the motive forces 

 equilibrate and the frustule remains stationary. In this way an explanation 

 is given of the extraordinary movements of foreign corpuscles down the 

 length of the raphe, which movements have been described by Max 

 Schultze ('). 



On the other hand O. Biitschli ( 2 ) and R. Lauterborn ( 3 ) explain the 

 movement of the large Pinnularia {major, nobilis, viridis) by an abundant 

 production of coleoderm. They placed the frustules in an emulsion of 

 Chinese ink and observed a current of isolated corpuscles which were 

 directed towards the central nodule down the whole length of an envelope 

 of coleoderm. This envelope was interrupted near the central nodule, and 

 there brought together the ink corpuscles which, as they came together, ended 

 by forming a kind of filament which lengthened out backwards. They also 

 assume that in this spot there is a filament of coleoderm projected, which, by 

 its re-action against the moving water, brings it to a standstill. 



Mr. Otto Muller ( 4 ) ( s ) confirms, it is true, these observations but rejects 

 the conclusions they would draw from it. Often, and notwithstanding a rapid 

 movement, the presence of a filament cannot be demonstrated, so that for 

 this reason the movement cannot be attributed to the projection of a 

 filament. 



According to Mr. Muller, the filament is only formed by the momentary 

 stopping of the protoplasm when animated by a backward movement in front 

 of the aperture of the central nodule. Moreover, by introducing oxygen into 

 his cultures those individuals which are without coleoderm can be made to 

 move. Mr. Muller believes that the protoplasm of the three species of 

 Pinnularia (namely, major, nobilis, viridis) secretes a glaireous matter, which is 

 fairly consistent and vibratory, possessing analogous qualities to that of the 

 jelly of the conjugatae described by Klebs. The minute and light granules of 

 Chinese ink do not succeed in penetrating into the glaireous bed. Conse- 



(*) Max Schultze : Die Bewegung der Diatomeen. Archit. f. Mikrosk. Anatomie Bd. i, Sep. , 

 p. 376, taf xxiii. Bonn, 1865. 



( 2 ) O. Biitschli: Bewegung der Diatomeen Verh. d. Natur. Hist. Med. Ver. zu Heidelberg, 

 N.F., Bd. iv., Heft 5. 



( 3 ) Robert Lauterborn : Zur Frage nach der Ortsbewegung der Diatomeen Berichte d. Deutsch 

 Botan. Gesellsch (1894) Bd. xii., p. 73. 



(4) Otto Muller: Die Ortsbewegung der Bacillariaceen betreffend. Berichte d. Deutsch. Bot. 

 Gesellsch. (1893) xi., p. 571. 

 (S ) Otto Muller : Die Ortsbewegung II. Berichte d. Deutsch Bot. Gesellsch (1894) xii., p. 136. 



