24-2 JELLY-FISH, STAR-FJSH, AND SEA-URCHINS. 



more complete trial, I dissolved various neutral 

 salts and other substances, such as sugar, etc., in 

 fresh water till it was of the density of sea- water ; 

 but in all cases, on immersing Sarsine in such solu- 

 tions, death was as rapid as that which followed 

 theii- immersion in fresh water. 



The Fresh-iuater Medusa. 



On June 10, 18S0, it Avas noticed that the 

 fresh water in the large tank of the lily-house of 

 the Royal Botanical Society, Regent's Park, was 

 swarming with a small and active species of Medusa, 

 previously unknown to science — it being, indeed, at 

 that time unknown to science that any species of 

 Medusa inhabited fresh water, altliough it was well 

 known that some of the other Hydrozoa do so. 

 Examination showed that the new species belonged 

 to the order TrachomedusiB, and the Petasidsp of 

 Jfaeckel's classification — its nearest known relative, 

 according to Professor Ray Lankester, being the genus' 

 Aglauropsis, which occurs on the coast of Brazil. 

 The Medusa was called Limnocodium (Xijuvri, a 

 pond, and kw^wv, a bell) sorbii by Professors All" 

 man and Lankester. I am indebted to the kindness 

 of Professor Allman for permission to reproduce his 

 drawing of the animal. Fig. 31.) It is remark- 

 able that, although this J.Iedusa has reappeared 

 every June in the same tank, no one has yet suc- 

 ceeded in tracing its life-history. Nor is it known 

 from what source the tank first became impregnated 

 with this organism. No doubt the germs must 



