Page:Essay on the mineral waters of Carlsbad (1835).pdf/110

 in day-time, and at the light of a lamp, I could not observe any motion.

Several Oscillatoriae creep only during the night and in dark places.

Upon many of them, as well as upon various Naviculae and Frustuliae, light exercices a manifest influence. When kept in cylindrical glasses, they move towards the lighted side, and abandon the dark one. I avail myself of this circumstance, when I want to catch the finest specimens. When preserved in china vases, filled with water, they reach very soon the surface or the sides of the water, when exposed to light.

In day-time, the Surirella Venus closes more its cuirass, which is never seen open but in dead individuals. During the night, and at the weak light of a lamp, I found many of them open, but they closed quickly their valves, when I directed upon them a more intense light.

I have very seldom seen the points of the Pediastra bending and moving themselves, and it is equally rare to see the Closteria crooked; but these motions were much more frequent in the animalcule, when exposed to galvanic or electric strokes.