THE ZOOLOGIST 



FOR 1855. 



Memoranda of Observations made in small Aquaria, in which the 

 Balance between the Animal and Vegetable Organisms was 

 permanently maintained. By Robert Warington, Esq.* 



Fresh Water. Memorandum I. — In my communication, dated 

 September, 1852,t I gave a detailed account of my observations on 

 the thread or web which some species of the fresh-water 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 Limneae. Iu continuation of my observations on the same 

 subject, I have now to state that the varieties of Planorbis, as also 

 Neritina 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 succeeded in raising the snail completely out of the water 

 a space of about seven 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 con- 

 sider that I am justified in stating that all the fresh-water snails are 

 possessed of this power. 



* Read at the Liverpool Meeting of the British Association, and communicated 

 by the author. 



f Published in the ' Zoologist' for 1852, p. 3633. 

 XIII. B 



