16 KILLING. 



chromic acid on to the surface of the water containing them, and 

 allowing it to diffuse slowly into it. About twelve to twenty-four 

 hours is necessary. He kills Ciona in a similar way with a mixture of 

 1 part of 1 per cent, chromic acid and 9 parts of 49 per cent, acetic 

 acid. 



Osmic acid, or Klein enberg's solution, is sometimes employed in the 

 same way. 



I have seen Medusae killed in a satisfactory manner by means of 

 crystals of corrosive sublimate added to the water containing them. 



Morphia, Curare, Strychnin, Prussia Acid, and other paralysing 

 drugs, have also been employed. 



26. Asphyxiation may be sometimes successfully practised. 

 Terrestrial Gastropods may be killed for dissection by putting them 

 into a jar quite full of water that has been deprived of its air by 

 boiling, and hermetically closing it. After from twelve to twenty- 

 four hours they are generally found dead and extended. The effect 

 is obtained somewhat quicker if a little tobacco be added to the 

 water. 



Good results are sometimes obtained with aquatic animals by 

 simply leaving them to exhaust the oxygen of the water in which 

 they are contained. I have sometimes succeeded with Holothurise 

 and other Echinoderms in this way. WAED (see Amer. Nat., xxv, 

 1891, p. 398) has succeeded with Hydroids, Actiniae, and similar 

 forms, and UEXKULL (Mitth. Zool Stat. Neapel, xii, 1896, p. 463) 

 with Echinids. 



Marine animals are sometimes successfully killed by simply 

 putting them into spring water. 



Warm Water will sometimes serve to immobilise and even kill 

 both marine and fresh- water organisms. 



Carbonic Acid Gas has been recommended (by FOL, Zool. Anz., 

 cxxviii, 1885, p. 698). The water containing the animals should be 

 saturated with the gas. The method is stated to succeed with most 

 Ccelenterata and Echinodermata, but not with Molluscs or Fishes. 

 I have had most excellent results with small Annelids and Hirudinea. 

 It is not necessary to employ a generator for obtaining the gas. It 

 suffices to take an ordinary " soda-water " syphon, and squirt its 

 contents into the water containing the animals. 



Narcotisation is very rapidly obtained with very small animals, 

 but much more slowly with larger ones. For instance, Stylaria 

 proboscidea, I find, is paralysed in a few seconds ; a small NepJielis 

 of 15 or 20 millimetres in length, will require about five minutes ; 

 and a large Nephelis, of from 10 to 15 centimetres, will require as 

 many hours. 



UEXKULL (Mitth. Zool. Stat. Neapel, xii, 1896, p. 463) has paralysed 



