110 METHODS OF COLLECTING AND PRESERVING 
spherical blobs of jelly ; others are provided with a skeleton of silex 
or of vitreous horny substance. 
As a general rule the tovving-net is emptied into a glass vessel 
of sea-water ; on adding a few drops of 1 per cent, osmic acid, the 
Radiolaria die, and sink to the bottom ; the sea-water is poured off 
oi 1 siphoned off, the residue washed in fresh-water, and treated 
with weak, and later with strong spirit. A simpler method is to 
put the animals direct into weak spirit, and later into strong spirit. 
Another method consists in the use of a 3 to 5 per cent, solution of 
formalin. 
Porifera (Sponges). 
Sponges live in all depths, and occur both in the sea and in the 
fresh waters of rivers, lakes, and ponds; and they vary extremely in 
colour, form, and consistency. 
They often encrust stones, rocks, sea-weeds, etc.; or they may be 
massive or arborescent. 
Fresh-water sponges are often of a brilliant green colour, and 
may be mistaken for water plants ; in dark places the green colour 
is replaced by pale buff. They grow on the piles of bridges and 
locks, or on the stems of water-weeds. 
On the banks of the Amazon specimens are found high and dry on 
the branches of bushes and trees which have been submerged during 
the rainy season, the blackish or earthy clumps of sponges often 
being mistaken for ants’ nests. Shallow-water sponges are often 
found in shady places under rocks or in caves. 
Notes should be taken of the colour of living sponges. 
Specimens growing on pier-piles may be raked up with a rake 
or a Dutch hoe with a bag of bolting-cloth conveniently fixed 
beneath. Forms living in deeper water are obtained with the dredge. 
To preserve sponges, they should be killed as soon as possible by 
putting them into strong spirit, or into a 10 per cent, solution of 
formalin. The latter, however, is not recommended as the best 
material, because it appears to act rather as a temporary disinfectant 
than as a permanent preservative. Formalin should not be used 
for calcareous sponges. The preserving medium should be changed 
after twenty-four hours. 
