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. 



' 



