.556 Notes. 



amount of oxygen set free, first from the forward and then from 

 the rear half of the organism. This accounts for the hesitancy 

 and irregular movements, as well as the motion forward and back- 

 ward over the same course. 



The evolving gas seems to act at times as a propeller to push 

 the organism forward, and at other times to exert a pulling action 

 to raise the growth on end. The various movements described 

 are the resultants of varying proportions of both of these active 

 forces. 



The fact that a longitudinal groove on the under side of the 

 artificial diatom causes it to become more active, due to the ex- 

 pulsion of the gas along the line of the groove, explains the reason 

 for the greater activity of the Kaphidere. 



The most interesting and peculiar movements among diatoms 

 are those of Bacillaria paradoxa, whose frustules slide over each 

 other in a longitudinal direction until they are all but detached, 

 and then stop, reverse their motion, and slide back again in the 

 opposite direction until they are again almost separated. When 

 the diatoms are active these alternating movements take place with 

 very considerable regularity. It is probable that the individuals 

 in a group of Bacillaria are joined together much more loosely 

 than other laterally attached genera, and that when a forward 

 movement takes place in the outer individual it is arrested by 

 capillarity just before the diatom is completely detached. 



It can now be readily seen that the strange movements of 

 the other microscopic plants may be explained as also due to the 

 evolution of oxygen gas. While the movements of desmids are 

 not as strongly marked as those of diatoms, many of them, notably 

 Penium and Closterium, have often been described as having a 

 power of independent motion, and Stahl * found that this motion 

 is greatly affected by light. 



The best account of the movements of desmids has been given 

 by Klebs.f This author speaks of four kinds of movements in 

 desmids, viz. : — 



1. A forward motion on the surface, one end of each cell 

 touching the bottom, while the other end is more or less elevated 

 and oscillates backwards and forwards. 



2. An elevation in a vertical direction from the substratum, 

 the free end making wide circular movements. 



3. A similar motion, followed by an alternate sinking of the 

 free end and elevation of the other end. 



4. An oblique elevation, so that both ends touch the bottom, 

 — lateral movements in this position ; then an elevation and circular 

 motion of one end, and a sinking again to an oblique or horizontal 

 position. 



* Verhandl. Phys. med. Geeell. Wurzburg, 1880, p. 24. 

 t Biol. Contralbl., 1885, p. 353. 



