THE BALANCE OF LIFE IN THE AQUARIUM. 437 



expire day and night, is as essential as oxygen is to the animal 

 economy, and thus, without introducing a single scrap of any living 

 plant, the halance is sustained, and death seems to be kept at a dis- 

 tance. If at first I threw in a tuft of callitriche or anacharis, or 

 any other true aquatic vegetable, oxygen would be supplied abun- 

 dantly ; and in practice it might be well to begin so, because some 

 little time elapses ere the seeds of the microscopic forest, the tops 

 of whose trees present to the eye but a felt-like coating of super- 

 ficial greenness, are developed into true plants ; though with a fair 

 amount of indirect daylight, and at certain seasons of the year, a few 

 hours suffice to set the vegetative process, with all its proper conse- 

 quences, in full action. Many of the readers of this paper will call to 

 mind the aquarium that stands in my entrance-hall. It contains 

 twenty fishes, large and small, and not a single scrap of vegetation ex- 

 cept what has been developed in situ by spontaneous generation. It 

 is three years since that was fitted and stocked, and committed to the 

 management of Nature, with the sole exception of the external aid 

 afforded by regular supplies of food for its inmates, which need not be 

 taken account of, now that we are considering it as a world in which 

 the balance of life and death is sustained by the operation of principles 

 ordained by the Creator. 



It is when we leave the principles and attempt to classify the details 

 of the scheme that we become bewildered. The smooth revolution of 

 the fly-wheel and the noiseless oscillation of the piston convince the 

 unprofessional observer of a great engine that mechanical motions are 

 possessed of poetry ; but, if he would analyze the relations of the cog- 

 wheels, the indications of the " governor," the " gauge," and the press- 

 ure-valve, he must descend to hard facts, and forget for a while the 

 sublime suggestions of a system of mechanism that throbs like a living 

 creature. Admit a full glare of summer sun to the aquarium, and forth- 

 with the water loses its pellucid fluidity, and becomes deeply tinged 

 throughout of a dull green, as if some pigment had been dissolved in 

 it. Instead of plants attached to stones and glass only, and animals 

 that float unseen, the whole of the water is occupied by visible masses 

 of animal and vegetable life ; and, if the fishes suffer, it will be from 

 undue heat, not from the addition to the element in which they live of 

 this new mass of being. Shut out the sunshine, let the fresh air play 

 over the surface of the water, let moderate daylight stream through it 

 as before, and speedily the green fog clears away, the water again 

 becomes transparent, and the balance is restored. Monas, euglena, 

 uvella, cryptomonas, gonium, and other wondrous infusoria, may be 

 detected as constituents of the cloudy mass while it lasts, called into 

 being because the conditions of the tank were such as they required, 

 as if life in embryo were everywhere locked up until the moment came 

 for its liberation, and some particular circumstance was the talisman to 

 set it free or, if we consider created forms to be marshalled in grand 



