854? FEESH-WATUU ALG^E. \_C7iIorosperme6e , 



able in this motion, which he considers as partly external, 

 and altogether physical. Their filaments, he says, are very 

 straight and elastic, and when they are placed for observa- 

 tion on the field of a microscope, they are bent out of their 

 natural straight line, and make an effort to recover it. 

 Currents almost imperceptible in the liquid in which they 

 are immersed, and perhaps unequal attractions among the 

 filaments themselves, are causes amply sufficient to explain 

 any motion, he thinks, that he has ever witnessed amongst 

 the Oscillatoriece. Captain Carmichael, however, a very 

 accurate observer, is of a difi^crent opinion, though he pro- 

 bably makes too much of their motion when he considers 

 it a proof of animal life. '^ Let a small portion of the 

 stratum be placed in a watch-glass nearly filled with water, 

 and covered with a circular film of talc, so that its edge 

 may touch the glass, the water will be rendered as fixed as 

 if it were a piece of ice. The glass may now be placed 

 under the microscope, and the oscillation of the filaments 

 viewed without the risk of disturbance from the agitation 

 of the water; by following this course it will be speedily 

 perceived that the motion in question is entirely independent 

 of that cause." 



2. OSCILLATORIA TIIERMALIS, IlaSSall. 



