VARIOUS INVERTEBRATE ANIMALS. 113 



superfluous water is drawn off, and a saturated solution of picric acid 

 is added suddenly ; if a precipitate of cocaine is thrown down, it is 

 removed, and fresh picric acid added, the Medusa being left in for 

 half an hour, and finally treated with 5 per cent., and later 10 per 

 cent., solution of formalin. 



Larger Medusae {Pelagia, Rhizostoma, etc.) are killed by adding to 

 the sea- water in which they are swimming 3 per cent, of a 1 per 

 cent, solution of osmic acid. As soon as they begin to assume a 

 pale brown tint, they are washed in fresh-water for two minutes, and 

 put into 35 per cent, alcohol, and later into 70 per cent, alcohol. 

 Mr. Hornell,* of Jersey, reports favourably on 5 per cent, formalin, 

 but perhaps the 10 per cent, solution is safer. 



Eor larvae of Scyphomedus?e (Sci/phistoma, Strohila) Signor Lo 

 Bianco recommends killing with warm corrosive sublimate, washing 

 in fresh- water, and grading into spirit. 



Ctenophora. 



Small forms are treated with osmic acid and alcohol, according to 

 the method given above for the large Medusas. 



Signor Lo Bianco recommends that they should be killed by 

 allowing them to fall into chrom-osmic acid mixture (100 ccm. of 

 1 per cent, chromic acid and 2 ccm. of 1 per cent, osmic acid), and 

 allowed to remain in for from fifteen to sixty minutes, according 

 to size, and then graded into alcohol up to 70 per cent. 

 . Formalin should not be used for preserving Ctenophora. 



Anthozoa. 



The first care must be to place the forms belonging to this 

 gi'oup in fresh salt-water, to allow them to expand — a result 

 which may not be obtained in some cases for twenty-four hours. 

 Alcyoiiarians should be killed with chrom-acetic solution No. 2,t 

 withdrawing the water in Avhich they lie until there is left just 

 enough to cover them, and then adding a volume of the chrom- 

 acetic solution double that of the sea-water. The animals should be 



* Hornell, " Natural Science," 189."), VTT., p. 410. 



f Concentrated acetic acid 100 ccm., 1 per cent, chromic acid 10 ccm. 



