104 METHODS OF COLLECTING AND PRESERVING 
When several specimens are put into one bottle, each should be 
tied up separately in rags. Large specimens may be preserved 
dry, by immersing for two hours in fresh-water, followed by 
immersion in ordinary alcohol for one day, and then by exposure 
to sun and air. 
To preserve the delicate calcareous Ascon sponges so as to be 
available for purposes of research, Professor Minchin* takes with 
him, on his collecting excursions, bottles containing 1 per cent, 
osmic acid, distilled water, and picrocarmine solution. The sponge 
is put into a bottle containing equal parts of sea-water and 1 per 
cent, osmic for from five to ten minutes. The specimen is rinsed 
in fresh or distilled water, and placed in picrocarmine for from one 
to two hours. Lastly, it is washed in distilled water, and transferred 
to glycerine or alcohol. 
Hydrozoa. 
Hydroida (Sea-firs, etc.). — The more commonly known species 
form branching treelike colonies rooted to stones, rocks, etc. 
Shallow-water forms will be found in pools left by the tide ; 
those from deeper water, often attached to stones or to the shells 
of molluscs and similar objects, are obtained by dredging. 
The fresh-water forms Cordylophora and Hydra occur in rivers, 
docks, etc! 
Specimens should be preserved in spirit or in 10 per cent, 
formalin. 
Moseley f recommended the following method for obtaining 
specimens with expanded polyps : — The living specimens are placed 
in a tall jar, with just enough sea- water, well aerated by shaking, 
to cover them. When the polyps are expanded, a hot saturated 
solution of corrosive sublimate is poured in. In a few minutes 
the sublimate solution is poured off, and fresh-water added, to be 
followed by weak and then strong spirit. 
Specimens of the fresh -water Hydra should be looked for on 
water plants. 
* " Quarterly Journal Microscopical Science," January, 1898, p. 474. 
f H. N. Moseley, "Admiralty Manual of Scientific Enquiry," 5th edit. 
Zoology, p. 357. 
