INTRODUCTION. 



between the Animal and Vegetable Kingdoms, by which 

 the vital functions of both are permanently maintained." 

 Mr. Warrington stated that he placed two small gold-fish 

 in a glass jar, capable of holding twelve gallons of water. 

 Half-filKng the vessel with spring-water, and placing some 

 sand and mud at the bottom, with pebbles and fragments 

 of limestone and sandstone, he planted a small Vallisneria 

 in the mud and left the whole undisturbed. After a time 

 the water became thick, and a coating of confervoid vege- 

 tation obscured the glass. On introducing, however, a few 

 water-snails, he found that they fed on the confervse as 

 well as on the decaying matter of the older leaves, and soon 

 restored the water to a clear and healthy condition. 



The pruning of the old leaves encouraged the growth 

 of off-shoots ; the snails flourished on the vegetable matter 

 which they consumed ; and the fishes lived healthily in 

 the renovated water, while they grew fat upon the eggs 

 which the scavengers deposited. I could not help regard- 

 ing with some veneration the veritable tank in which these 

 early experiments were made, with the same water un- 

 changed, when admitted to a view, through the politeness 

 of its possessor, only a few days since. 



In the year 1853, Mr. Warrington communicated in the 



