366 Mr. R. Warington's Notes on Animals in small Aquaria. 



the limestone deposits of the tertiary, of the cretaceous, or of the 

 oolitic, nay, even of the palaeozoic periods ; and the whole vege- 

 table carpet covering the present surface of the globe, even if we 

 were to consider only the most luxurious vegetation of the tro- 

 pics, and leave entirely out of consideration the whole expanse 

 of the ocean, as well as those tracts of land where under less 

 favourable circumstances the growth of plants is move reduced, 

 would not form one single seam of workable coal to be compared 

 to the many thick beds contained in the rocks of the carbo- 

 niferous period alone. 



XXXIV. — Memoranda of Observations made in small Aquaria, in 

 which the Balance between the Animal and Vegetable Organisms 

 was permanently maintained. By Robert Warington, Esq. 



Fiesh Water. 



Memorandum 1. 



In my communication, dated September 1852*, I gave a 

 detailed account of my observations on the thread or web 

 which some species of the freshwater snail form to effect or 

 facilitate their passage from one spot or object to another, and 

 thus either ascending or descending by its means; and the 

 instances noticed up to that period had reference only to the 

 varieties of the Limnece. In continuation of my observations 

 on the same subject, I have now to state that the varieties of 

 Planorbis, as also Nerilina fluviatilis and Physa fontinalis, have, 

 since that date, been noticed to possess the same power ; and in 

 the case of the latter, Physa fontinalis, the thread or web was so 

 tough and strong, that on one occasion I was able, by means of 

 a small rod introduced between the creature and its point of 

 attachment, to move it out of its straight course a considerable 

 distance, and by then slowly drawing the rod upwards, I suc- 

 ceeded in raising the snail completely out of the water a space 

 of about 7 inches, suspended by its thread, so that, under these 

 circumstances, the thread itself became distinctly visible. 



From the observations which I have been enabled to make, I 

 consider that I am justified in stating that all the freshwater 

 snails are possessed of this power. 



Memorandum 2. 



As an evidence of the permanency of the balance capable 

 of being established between the animal and vegetable organ- 



* Annals and Magazine of Natural History, Oct. 1852. 



