110 METHODS or 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 towing-net is emptied into a glass vessel 

 of sea-water ; on adding a few drops of 1 per cent, osmic acid, the 

 Kadiolaria die, and sink to the bottom ; the sea-water is poured off 

 or siphoned off, the residue washed in fresh-water, and treated 

 with weak, and later with strong spirit. A simpler method is to 

 put the animnls 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 houis. 



