312 Liunean Society. [Dec. 1, 



in contact. The direction of the movement is then again reversed, 

 and continues to alternate in opposite directions, the time occupied 

 in passing from the elongation in one direction to the opposite being 

 generally about 45 seconds. In the course of this movement the 

 filaments seldom resume their original Fragilaria-like appearance ; 

 and there are occasional interruptions to its regularity, both the ter- 

 minal frustules in some cases moving in one and the same direction 

 instead of in a direction opposite to each other. This Mr. Thvpaites 

 regards as resulting from a breach in the vital or dynamical con- 

 nexion of the filament, and as not improbably indicating the place 

 where spontaneous division of the filament is about to occur. If a 

 filament, while in motion, be forcibly divided, the uninjured frustules 

 of each portion continue to move as before, proving (as the author 

 believes) 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 still extremely rigid and requires some com- 

 paratively 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 move- 

 ment. 



The author hazards a conjecture that the action of cilia is the 

 proximate cause of the phsenomenon ; for, although he has been un- 

 able to discover cilia, he has little doubt of their presence from the 

 mode in which minute particles of indigo suspended in the water 

 were acted upon, when coming into contact with the frustules. He 

 regards the movement of each individual frustule, considered alone, 

 as closely resembling that which is seen in the detached frustules of 

 other sj)ecies of Diutomaceee ; namely, a so to speak alternate back- 

 ward and forward movement at regular intervals. On the animal or 

 vegetable nature of the production he has no remarks to offer. 



The paper was accompanied by magnified drawings of Bacillaria 



paradoxa in various stages of elongation and retraction ; and by very 

 highly magnified representations of its mode of fissiparous increase, 

 and of the markings on both its surfaces. 



Read also the commencement of a memoir " On the Vegetation of 

 the Galapagos Archipelago, as compared with that of some other 

 Tropical Islands and of the Continent of America." By Joseph Dal- 

 ton Hooker, Esq.. M.D., F.L.S. &c. 



