32 HYDROIDS, ETC. 
ually adding it to the water they are in. Small jellies 
should be treated to a weak solution of osmic acid, one 
tenth per cent water; this hardens their tissues. To pre- 
vent animals from closing up, kill in chromic acid (one 
and one half per cent), and place in alcohol. Living 
coral (Astrangia) can be dredged in Long Island Sound. 
Specimens can be hardened for sectional examination in 
osmic acid. 
A ship sailing at night through phosphorescent animals, as noctiluca 
(Fig. 6), jelly-fishes, ascidians, etc. 
