Animal and Vegetable Relations. 2869 



The materials' being thus arranged, all appeared to go on well for a short time, 

 until circumstances occurred which indicated that another and very material agent 

 was required to perfect the adjustment, and which, from my not having thought of it 

 at the time of commencing the experiment, had not been provided against. The 

 circumstances I allude to arose from the internal decay of the leaves of the Vallisneria, 

 which became yellow from having lost their vitality, and began to decompose ; this, 

 by accumulation, rendered the water turbid, and caused the growth of mucus, or 

 green, slimy matter on the surface of the water, and on the sides of the receiver. If 

 this had been allowed to increase, I conceive that the healthy life of the fish must 

 have suffered, and probably their vital functions have been destroyed. The removal 

 of these decaying leaves from the water, therefore, became a point of permanent im- 

 portance to the success of the experiment. To effect this, I had recourse to a veiy 

 useful little scavenger, whose beneficial functions have been too much overlooked in 

 the economy of animal life, — I mean the water-snail, whose natural food is the very 

 green, slimy growth, or mucus and decaying vegetable matter, which threatened to 

 destroy the object which was wished to be obtained. Five or six of these creatures — 

 the Liinnasa stagnalis — were consequently introduced, and, by their continued and 

 rapid locomotion and extraordinary voracity, soon removed the cause of interference, 

 and restored the whole to a healthy state, thus perfecting the balance between the 

 animal and vegetable inhabitants, and enabling both to perform their vital functions 

 with health and energy. So luxuriant was the growth of the Vallisneria under these 

 circumstances, that, by the autumn, the one solitary plant that had been originally in- 

 troduced, had thrown out myriads of off-shoots and suckers, thus multiplying to the 

 extent of upwards of thirty fine, strong plants ; and these threw up their long, spiral, 

 flowering stems in all directions, so that, at one time, more than forty blossoms were 

 counted lying on the surface of the water.* The fish have been lively, bright in 

 colour, and appear very healthy, and the snails also— judging from the enormous 

 quantity of gelatinous masses of eggs which they have deposited on all parts of the 

 receiver, as well as on the fragments of stone — appear to thrive wonderfully, and, be- 

 sides their functions in sustaining the perfect adjustment of the series, afford a large 

 quantity of food to the fish in the form of the young snails, which are devoured as 

 soon as they exhibit signs of vitality and locomotion, and before their shell has become 

 hardened. Thus we have an admirable balance sustained between the animal and 

 vegetable kingdoms, and that in a liquid element. The fish, in its respiration, con- 

 sumes the oxygen held in solution by the water as atmospheric air ; furnishes carbonic 

 acid ; feeds on the insects and young snails ; and excretes material well adapted as a 

 rich food to the plant, and well fitted for its luxuriant growth. The plant, by its 

 respiration, consumes the carbonic acid produced by the fish, appropriating the carbon 

 to the construction of its tissues and fibre, and liberates the oxygen in its gaseous 

 state to sustain the healthy functions of the animal life, at the same time that it 

 feeds on the rejected matter, which has fulfilled its purposes in the nourishment of 

 the fish and snail, and preserves the water constantly in a clear and healthy condition, 

 —while the slimy snail, finding its proper nutriment in the decomposing vegetable 



* Since the reading of this paper, twenty-eight strong plants of Vallisneria have 

 been weeded out of the glass receiver as being more than sufficient for the purpose 

 required. — i?. W. 



VIII 2 H 



