HISTORY OF DIATOMS. II 



learned and skilful correspondent has been good enough to draw up for 

 this work. 



From his recent investigations on the mechanical causes of their motion 

 Mr. Otto Miiller concludes that the movements of diatoms must be regarded 

 as produced by the resultant of motive forces which are generated on the 

 surface of protoplasmic currents. His theory contains the mechanical basis 

 of these movements, and clearly brings out its essential particulars in the 

 following manner: 



Mr. O. Muller ( ' ) in the first place proves the existence of a very compli- 

 cated system of c.maliculi and anastomosing fissures which run across the 

 side of the valve of the largest species of Pinnularia, and must be regarded 

 as designed to conduct a fluid medium from the interior towards the external 

 side of the cell. The central and terminal nodules are sulcated by straight 

 and curved canaliculi, which run towards the raphe and are lost in it. In 

 addition to this Mr. Muller has shewn that the lithoplasm has a considerable 

 internal pressure. According to him, in consequence of this pressure the 

 living plasm starts out through the canaliculi of the central and terminal 

 nodules, and runs into and courses down the whole length of the raphe 

 against the external surface of the cellular wall, so as to return by the 

 canaliculi of the terminal or central nodules into the interior of the cell. 

 The re-action of the motive forces, at the surface of the living plasm, upon 

 the surrounding medium is the cause of the movement of the frustules. 



At the surface of the Pinnularia are seen four courses of currents (two on 

 each valve). Each of them is independent in this sense, that of itself the 

 current can proceed from a terminal to the central nodule or inversely, or 

 can even momentarily stop. This gives rise to a great variety of force 

 combinations, and consequently of directions of movements since the dis- 

 placement is produced in the direction of the resultant of all the motive 

 forces which simultaneously act in the courses of the currents. The par- 

 ticulars of their displacement, their backward and forward motion, their 

 deviations from the straight line, &c, are easily explained by basing them on 

 the preceding considerations. 



As a rule, a plasmatic current starts from each side of the polar cleft of 

 the anterior terminal nodule (the notions of back and front being derived 

 from the direction of the movement) moves towards the central nodule and 

 returns by the anterior opening of the central nodule into the interior of the 

 cell. Outside of the posterior opening of the central nodule, there starts on 



(') Otto Miiller: Durchbrechungen der Zellwand in ihren Beziehungen zur Ortsbewegung der 

 Bacillariaceen. Berichte d. Deutsch. Bot. Gesellsch, 1889, Bd. VII., pp. 169 180. 



