18 CHAPTER II. 



Holothurias and other Echinoderms in this way. Waed (see 

 Amer. Nat., xxv, 1891, p. 398) has succeeded with Hydroids, 

 Actinias, and similar forms, and Uexkijll {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 Eol, Zool. 

 Anz., 128, 1885, p. 698). The water containing the animals 

 should be saturated with the gas. The method is stated to 

 succeed with most Ccelenterata and Bchinodermata, 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. Eor 

 instance, Stylaria 2Jroboscidea, I find, is paralysed in a few 

 seconds; a small Nephelis 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. 



Uexktjll (iMUfh. Zool. Stat. Neafel, xii, 1896, p. 463) 1ms 

 paralysed Echinids very rapidly with carbonic acid, likewise 

 a small Teleostean fish ; whilst Scyllium and Crustaceans 

 were affected much more slowly, and mussels not at all. 



27. Peroxide of Hydrogen.— Volk {Zool. Anz., xix, 1896, 

 p. 294) kills Rotatoria by means of one or two drops of a 

 o per cent, solution added to 1 c.c. of the water containino- 

 til em. 



