OR, TIIE HOME-CULTURE OF FRESH-WATER PLANTS. 
After the reading of the foregoing paper, it was 
remarked by Professor Balfour that the motions in 
question might be the result of the growth of the cells 
of the plant; hut Dr. Lanlcester considered them en¬ 
tirely owing to the proteinaceous protaplasm within 
the cell, a matter which, both in plants and ani¬ 
mals, is known to possess a contractile power. It 
was the source of the movements in the Proto- 
phyta and Protozoa , and might he regarded as 
containing the essential elements of a nervous 
and muscular system. So far Dr. Dankester\s 
argument agrees with the theory of Professor 
Knowles; hut he omitted to state whether he con¬ 
sidered the movements voluntary or not, so that 
this interesting physiological question is still an 
open one. 
It will he seen, from these observations, that the 
keeping of an Aquarium should always he accompa¬ 
nied by the possession of a microscope, with the aid 
of which it is evident that an abundant, curious, and 
instructive course of investigation need never flag, 
while the inmates of the tank are kept in that flou¬ 
rishing condition, which a proper attention to the 
principles upon which it is founded cannot fail to 
secure. 
45 
