DESMIDIACE.E 581 



lengthens. The movements of desmids are especially active when 

 they are in the process of dividing. Stahl found that, like the move- 

 ments of zoospores, they are affected ly light, and always move 

 towards the light. 



A ' cyclosis ' may l>e readily observed in many Desinidic<;< . 

 and is particularly obvious along the convex and concave edges of 

 the cell of any vigorous specimen of Closterium, with a magnifying 

 j tower of 250 or 300 diameters (fig. 436, A, B). By careful focus- 

 sing the flow may be seen in broad streams over the whole surface 

 of the endochrome ; and these streams detach and carry with them, 

 from time to time, little oval or globular bodies (A. b) which are put 

 forth from it. and are carried by the course of the flow to the tran> 

 parent spaces at the extremities, where they join a crowd of similar 

 bodies. In each of these spaces (B) a protoplasmic flow proceeds 

 from the somewhat abrupt termination of the endochrome towards 

 the obtuse end of the cell (as indicated by the interior arrows). 





FIG. 436. Cyclosis in Closterium luimla : A, cell showing central separation at a, 

 in which the large particles, b, are not seen ; B, one extremity enlarged, showing 

 the movement of particles in the colourless space ; D, cell in a state of division. 



and the globules it contains are kept in a sort of twisting movement 

 on the inner side () of the parietal utricle. Other currents are 

 M-en apparently external to it, which form three or four distinct 

 courses of particles, passing towards and away from c (as indicated 

 by the outer arrows). Another curious movement is often to be 

 witnessed in the interior of the cells of members of this family, 

 which has been described as 'the swarming of the granules/ from 

 the extraordinary resemblance which the mass of particles in active 

 vibratoiy motion bears to a swarm of bees. It is especially 

 observable in the hyaline terminal portions of the cells of specie-; of 

 Closterium, as shown in fig. 436, B. This motion continues for 

 some time after the particles have been expelled by pressure from 

 the interior of the cell ; and it appears to be an active form of the 

 molecular movement common to other minute particles freely sus- 

 pended in fluid. This movement of minute particles affords an 

 instance of the phenomenon known as ; Brownian movement,' and 

 is probably of a purely mechanical nature. 



