CORDYLOPIIORA LACUSTRIS. 253 



Development of Gonosome. — June to August. 



HahUut. — Attaclied to the under surface of floating timber, and to various submerged bodies 

 in fresh and slightly braekish water. 



Localities. — Grand Canal Docks, Dublin, G. J. A. ; Commercial and West Indian Docks, 

 London, Dr. Bowerbank and G. ,I.A. ; a freshwater cistern near London, Busk; agricultural 

 drains near Lynn Regis, Dr. Lowe ; canal near Ostend, Van Beneden ; Schleswig, Semper ; 

 neighbourhood of Stockholm, Retzius ; near Rostock, F. E. Schulzc. 



I first met with Cordi/lopliora lacmtris on tJie l)ottom of an old canal boat which had 

 been lying for a long time in the docks of the Grand Canal, near Dublin. Tliese docks form 

 the termination of a canal which receives its supply of water from lakes in the interior of the 

 country. The docks are many feet above the river Litfey, from which, however, vessels can be 

 admitted into them by means of a lock ; and though the part of the river with which they can be 

 thus made to communicate is uiuler the influence of the tide, the quantity of salt water which 

 may get access to the docks at the time when vessels enter them from the river is altogether 

 inappreciable. 



Cordi/Iophora tacustris occurs also very abundantly and in great perfection on floating timber 

 in the Commercial and West Lidian Docks on the river Thames, where it is accompanied by 

 Spongitta Jlumatitis, and by Hydras, freshwater Polijzoa, and other freshwater mollusca, as well 

 as by Potomogetons, Lemnas and various other freshwater plants. Here also any sea water which 

 during the entrance of vessels may get admittance to the docks is quite inappreciable to the taste. 



But the Cordi/Iophora has been also found in water supplied to the inhabitants of London for 

 drinking and other domestic purposes, for Busk has identified with it a hydroid met with in a 

 dark cistern filled with water obtained for these purposes from the river Thames. Quite recently 

 it has been found by Professor Van Beneden on shells of Dreissena poljjmorplia, and on timber 

 from a canal near Ostend. Specimens of Cordylopliora tacustris have been kept alive and in 

 health by myself for many weeks in the ordinary drinking water of the City of Dublin. This 

 water is brought from freshwater lakes which lie far away in the interior of the country, so that 

 there can be no question as to the present species living and thriving in absolutely freshwater. 



I must here mention, however, that specimens obtained in the West Lidian Docks were, 

 after having been brought to Edinburgh, placed in some of the water supplied to the inhabitants 

 for domestic purposes, where they continued to live for some weeks, but with an evident loss of 

 vigour ; many of the hydranths had fallen off the branches, and fresh buds were but feebly 

 produced. Li this state of things I added a very small quantity of sea water to the fresh water 

 in my jars — less than one hundredth part of the whole— when my specimens, after a few days, 

 had quite recovered their original vigour, and had begun to throw out al)undance of healthy 

 hydranth buds. 



From this it would seem that the specimens from the West Lidian Docks were unable to 

 dispense, at least suddenly, with the very minute quantity of sea water which may occasionally 

 gain access to the Docks, a quantity so small as to be entirely inappreciable to the sense of taste, 

 and which in no way interferes with the healthy growth of truly freshwater animals and plants 

 which, along with the Corydytophora, are found abundantly in the Docks. 



It is highly probable that Cordytopltora lacmtris is an introduced species, possibly imported 

 into this country, as Breissena potymorpha has been supposed to be, on foreign timber, and like 



