FIXING AND PRESERVATIVE MEDIUMS 51 



polyps, which they tend to distort, a gentle tap or two upon 

 the vessel will disperse them. 



Some of the Pennatulidse are, says Lo Bianco (p. 447), 

 when extended, seized by the naked base and plunged very 

 rapidly into a deep preparation-jar containing the foregoing 

 mixture ; after a few seconds they are transferred to a porce- 

 lain pan containing alcohol of 50 per cent. Then, with a 

 syringe and fine cannula, alcohol of 70 per cent, is injected 

 through a small hole made in the basal extremity. To ensure 

 the penetration of the alcohol, the tentacles are inflated, and, to 

 prevent the alcohol escaping, a ligature is tied around. 



Luidia (one of the " star-fishes ") is turned into a pan with 

 a little sea-water, and, when the feet are displayed, flooded with 

 the mixture. Immediately afterwards the animal is brought 

 into weak alcohol, followed as usual by strengths leading up 

 to 70 per cent. 



Echinoids ("sea-urchins") are killed with their ambulacral 

 feet extended, by being placed in a little sea-water and flooded 

 with the mixture. The transference into weak alcohol must 

 be made immediately, otherwise the acid will attack the cal- 

 careous test of the animal. 



39. — Chromic and Osmic Acid (Lo Bianco, p. 443) 



Chromic acid(i per cent.) . . . loo parts 



Osmic acid (i per cent.) . . . 2 „ 



Of the Trachymedusae, such forms as Rhopalonema, Cunina, 

 jSiginota, jEginopsis, Liriope, and Carmarina are fixed by the 

 above liquid in five to twenty minutes, according to their size, 

 afterwards washed in spring-water, and passed gradually into 

 the full strength of alcohol. 



Amongst the Ctenophora, Ber'de ovata, Hormiphora, Cal- 

 lianira, Lampetia, Euchlora, and young examples of Cestus, 

 Eucharis, and Bolina are narcotised and killed also by this 



