1050 General Notes. (October, 
ZOOLOGY. 7 
THE ORIGIN OF FRESH-WATER FAUNAS, A STUDY oF EvoLUTION. 
—Under this title Professor W. J. Sollas read a paper at a late 
meeting of the Irish Royal Society, which is reported in Nature 
for June 12.. As no reference has been made apparently to work 
done in this country, it will supplement Dr. C. A. White's essays 
on the same subject. The poverty of fresh-water faunas as com- 
pared with marine is commonly attributed to a supposed inadapta- 
bility on the part of marine organisms to existence in fresh-water, 
That this explanation is inadequate is shown by the existence of 
fresh-water jelly-fish, such as Limnocodium, and still more 
directly by the experiments of Beudant, who succeeded in accus- 
toming several kinds of marine mollusca to a fresh-water habitat. 
The view of Von Martens that the severity of a fresh-water 
climate is prohibitive of the existence of most marine forms it 
rivers is insufficient, and a more thoroughgoing explanation 1$ 
necessary. This is to be found in a study of the means by which 
the distribution of marine animals is secured. In the case 
stationary forms free-swimming embryos are distributed over 
wide areas by currents, and they can never pass from the sea into 
rivers, in which the current is always directed seawards. Nor, 
j lar 
mollusks do not enter upon a free existence until they are dal d 
to their parents, and Paludina is viviparous e suppress 
. tto 
yolk, and other kinds of nourishment furnished by the p d 
with 
the drudgery of working for its own existence, and supp 
nutriment in a form that puts the least tax on its digestive Popi 
a larger balance of energy remains available for metame 
probably leads to the lengthening of the adult life, an 
