PROF. G. J. ALLMAE* ON" LIMtfOCODIUM: VICTORIA. 131 



OnLimnocodium victoria*, anew Hydroid Medusa of Fresh Water. 

 By Prof. a. J. Allman, M.D., LL.D., F.R.S., President L.S. 



[Received June 14, 1880 ; Read June 17, 1880.] 



I am indebted to Mr. Sowerby, of the Botanical Society's Gardens 

 in Regent's Park, for having called my attention to the fact that 

 certain medusoid organisms had shown themselves in the gardens, 

 where they had become developed in great abundance in one of 

 the warm tanks devoted to the cultivation of the Victoria regia. 



So startling a fact as the occurrence of a medusa in fresh water 

 demanded immediate examination, and, through the kindness of 

 Mr. Sowerby, I was enabled to make a careful study of the re- 

 markable phenomenon to which my notice was drawn by him. 



A visit to the tank made apparent the correctness of Mr. 

 Sowerby's observation, for the water, which had a temperature of 

 86° Fahr., was literally swarming with little medusae, which varied 

 in size from about a line in transverse diameter to nearly half an 

 inch. They were most energetic in their movements, swimming 

 with the characteristic systole and diastole of their umbrella, and 

 apparently in the very conditions which contributed most com- 

 pletely to their well-being. 



A closer examination showed them to be true hydroid medusa?, 

 and revealed some very interesting structural features. The 

 umbrella varies in form with the state of contraction, passing 

 from a somewhat conical shape with depressed summit, through 

 figures more or less hemispherical, to that of a shallow cup. The 

 radiating canals are four in number and open into a wide mar- 

 ginal canal ; and the manubrium is large and, when extended, pro- 

 jects beyond the margin of the umbrella ; its lips are destitute 

 of tentacles, but everted and plicated (fig. 2). 



The marginal tentacles are filiform; they are numerous, 

 nearly 200 in old individuals, and are of unequal size. The longest 

 and thickest correspond to the points where the four radiating 

 canals open into the marginal canal. In each interval between 

 these, and at equal distance from one another, occur seven some- 

 what smaller tentacles, and between these again other still smaller 

 ones. The velum is of moderate width, and the extreme margin 

 of the umbrella is wavy and thickened and loaded with brownish- 

 yellow pigment-cells. 



* Instead of " victoria" Prof. Lankester employs the specific name Sowerbii, 

 after Mr. Sowerby, the discoverer of the medusa — a modification of the nomen- 

 clature used above, which I am quite willing to adopt. 



