POPULAR SCIENCE REVIEW. 
THE COMMON FEESH-WATER SPONGE-^>S^o?i^i^^C6 
fluviatilis, 
^ By professor W. C. WILLIAMSOM, FR.S. 
W HEN fishing amongst fresh waters, in ponds, reservoirs, or 
near the sides of large docks, the naturalist frequently 
brings to the surface masses of a green slimy substance, ad- 
herent to stones, or, more frequently, to sticks (fig. 1), posts, 
or other pieces of dead wood. The object is not attractive to 
the eye, and the impression it makes upon the olfactory sense 
is not such as to invite closer acquaintance on the part of the 
unscientific observer. But to the naturalist the Spongilla, or 
fresh-water sponge, is one of the most interesting of organ- 
isms. Its existence has long been known to students of nature. 
Ray and Pulteney were familiar with it. Linnseus received it 
from one of the Swedish lakes with intense satisfaction, and 
correctly discerning its close affinity to the marine sponges, he 
included it amongst them, giving to its two chief varieties the 
specific names of fluviatilis and lacustris, by the former of 
which it is still generally known. But though it has so long 
been a familiar object to zoologists, surprisingly little was known 
of its real history until within the last few years. In common 
with its spongy relatives, its claim to rank amongst animals has 
been extensively questioned. Mr. J. Hogg, some years ago, 
noted various phenomena, which led him to conclude that it was 
a plant. He specially observed that its green colour was largely 
dependent upon the action of light — a plant-like feature which 
had much weight with him and those who, like him, believed 
the Spongilla to be a vegetable form. 
Within the last few years, thanks to the labours of Carter, 
Lieberkuhn, and Bowerbank, but especiall}^ to the first-named 
VOL. VII. — NO. XXVI. B 
