438 THE POPULAR SCIENCE MONTHLY. 



procession, may we not expect that every tribe will hurry to its ap- 

 pointed place the instant that a door is opened?* 



Microscopists have long been at war, but without bloodshed, as tc 

 the place to be assigned to certain organic forms which are hidden 

 from our common eyesight. While the war goes on as to whether 

 desmidiacse and diatomacese be animal or vegetable, or both, let facts 

 suffice us here in the study of the aquarium. Does an animal exhale 

 carbonic acid ? Yes. Well, here are plants or animals, concerned in 

 keeping up the balance, which exhale oxygen, and their name is legion. 

 Volvox globator and the bacillariae labor as hard to supply the fishes 

 with the life-sustaining gas as do the silken threads of verdure that 

 line the glass like a carpet. Is the possession of starch a distinctive 

 feature of the vegetable? Perhaps so. Truly here are desmidiacaa 

 that contain starch, and, if I make the possession of cilia the test for 

 assigning certain forms to the animal kingdom, I find in the aquarium 

 spores of algse furnished with them. Motion I know to be no test, 

 because alga3-spores dance through the water gayly till they find a 

 resting-place, and, when the aquarium was first filled, it was by dancing 

 they at last found where to pitch their tents, and cease their nomad 

 wanderings. But they all work together to sustain the balance, and 

 the law of " give and take " prevails among them the stentor de- 

 vours the oscillatorise, rotatoria, and monads, and the hydras swallow 

 all ; every darting speck is a tomb wherein some smaller speck of life 

 is to be buried, and life thus prospers on the decay it is itself under- 

 going. 



But all this while a fine deposit slowly settles among the pebbles, 

 which form the lower stratum of this watery world. Between the 

 stones a fine alluvial silt collects and thickens. The first frost, suffi- 

 ciently severe to touch the tank, causes the whole green coating to peel 

 off from the glass and rock, and, while this subsides, to add to the 

 thickness of the alluvium how slightly, and yet how sufficiently for 

 an example of Nature's working ! a new growth commences, and 

 that balance is restored. Do you not see that the chief teaching of 

 geology the piling of stratum upon stratum, the conversion of dis- 

 rupted rock and decayed plant and animal into rock again is here 

 exemplified in the history of a domestic toy, which contains already 

 one example of stratification in the silence of watery submergence ? 

 A tank which has been fitted with loam, pebbles, and plants of the 

 brook and river, will, if left undisturbed for three years, be in this 

 state. Those plants will all have decayed, but there will be an abun- 

 dant spontaneous vegetation. The accumulations of that short period 

 will have settled into a close mass, almost as hard as stone ; and if 

 fishes have died in the mean time, and have not been removed, their 

 bones will be found overlaid with hardened mud, just as we find them 

 in the old red sandstone, or the chalk, or the carboniferous rocks, and 

 shall we not call them our own fossils ? See again in this case in which 



