ALG.'E. 175 



stationary, or nearly so — while each of the others has 

 moved with a rapidity increasing with its distance 

 from the centre, its own rate of movement having 

 been increased by the addition of that of the inde- 

 pendent movement of each friistule between it and 

 the central one. This lateral elongation of the fila- 

 ment continues until the point of contact between 

 the contiguous frustules is reduced to a very small 

 portion of their length, when the filament is again 

 contracted by the frustules sliding back again, as it 

 were, over each other ; and this changed direction 

 of movement proceeding, the filament is again drawn 

 out until the frustules are again only slightly in con- 

 tact. The direction of the movement is then again 

 reversed, and continues to alternate in opposite 

 directions, the time occupied being generally about 

 forty-five seconds. If a filament while in motion be 

 forcibly divided, the uninjured frustules of each por- 

 tion continue to move as before, proving that the 

 filament is a compound structure, notwithstanding 

 that its frustules move in unison. When the filament 

 is elongated to its utmost extent, it is extremely rigid, 

 aiKi requires some comparatively considerable force 

 to bend it, the whole filament moving out of the way 

 of any obstacle rather than bending or separating 

 at the joints. A higher temperature increases the 

 rapidity of the movement." ^ 



Without attempting any furthur description of 



these movements, which are well known to all those 



who have studied these organisms, we may observe 



that, although the hypothesis of ciliary motion has 



* Proceedings of the Linitcean Society, \o\. i. p. 311. 



