84 



FRESH- WATER SPONGES. 



birotulate spiculum in the wall of the statoblast. Hence we have 

 Meyenia finviatilis^ Meycnia phiTnosa^ and many others, the former 

 of these standing, in a sense, as representative of the genus. The 

 birotulate spicula resemble, somewhat, two car-wheels, with the 

 uniting shaft in position ; the rotulae being smooth, or dentate, or 

 of other form in the different species. Meyenia flmiatilis is 

 perhaps the most common of the sponges, and may be found in 

 most rivers, ponds, and lakes. In my own experience, I find this 

 and many other species most abundant in slowly running or in still 

 but fresh water. They are found on the under sides of sub- 

 merged logs, pieces of wood, and stones, as well as on weeds of 

 different kinds. I have sometimes found them growing on the 

 ground, where they were partly obscured by weeds. Darkness 

 seems favourable to their growth, though not at all essential. The 

 appearance of the fresh-water sponge, in some localities, and when 

 mature, is not very different from that of our ordinary domestic 

 sponge (which, in passing, is nothing more than the fibrous 

 skeleton of a marine sponge). Sometimes they are green, and 

 take on several hues, which I regard as of no specific value. 



Sponges are found mature in October and November, at which 

 time they will generally abound in statoblasts. Some species 

 have an abundance of these as early as the latter part of June. 

 They may then be found on the under-sides of stones, like a thin 

 network, the statoblasts being very conspicuous. 



In Mr. Carter's classification, the term Spongilla is used for his 

 first genus, which includes many species, at the head of which 

 stands Spongilla laaistris, one of the oldest of the sponges, and 

 the representative of its genus. This is one of the most widely 

 distributed, it having been found in America, from Nova Scotia to 

 Vancouver's Island. Dr. Dybowski, of St. Petersburg, has found 

 it in seventeen places in Russia, including the south-west of Lake 

 Baikal, in Asia. I have found this sponge growing on stones in 

 rather swiftly-running water. The water was shallow and rippling. 

 The sponge was green, and might easily have been mistaken for an 

 alga. On raising the stones, I found the sponge of a dull buff 

 colour on the under-sides. Sponges of many kinds may be found 

 by raking up the weeds from the bottom of sloughs, or ponds, or 

 in any sluggish water, where they attach themselves to Anacharis^ 



