NOTES AND MEMORANDA. 
Medusse andHydroid Polyps living in Fresh Water — From 
experiments made by Mr. Romanes on Limnocodium, and 
published in ^ Nature ’ of June ^4th it appears that the fresh- 
water Medusa is very intolerant of sea water. It cannot be 
re-introduced with impunity, to the medium in which fts 
ancestors originally lived, and this would seem to imply that 
a very great length of time has elapsed since the adaptation 
to fresh water took place. Curiously enough, Mr. Romanes 
has found that marine Medusae are not so injuriously affected 
by brine as the Limnocodium is by sea water. The fact, 
however, is less astonishing when we remember that the 
percentage of saline matter in solution in sea water is many 
hundred times what it is in average pond water, whilst 
the strongest brine has not a percentage of saline matter 
many times in excess of that of sea water. 
On the whole the tolerance by marine animals of fresh 
-water is a much more frequently observed fact in all classes 
than the tolerance of sea water by lacustrine or fluviatile 
forms. It is undeniable that existing fresh water forms have 
been developed by adaptation from marine forms, whilst it is 
difficult to cite any instance in which adaptation in the 
opposite direction appears to have taken place ; some few 
marine Oligochsetous Chaetopods and Pulmonate Gastero- 
pods being perhaps such instances. 
The tolerance by Medusae belonging to marine species of 
fresh -water under natural conditions was observed by Mr.' 
Moseley, at Browera Creek, in New South Wales, and from 
Professor Alexander Agassiz I have received some interest- 
ing notes recording similar observations. 
Mr. Moseley says (‘Naturalist on the Challenger,^ p- ST2), 
“ After heavy rain the surface water in all the upper parts 
of the creek is so diluted by the torrent of fresh water from 
the stream, that it becomes almost fresh ; indeed, at the time 
of our visit, it was for three or four miles down so little 
brackish as to be drinkable. .At a short depth no doubt the 
