and more satisfactory method is to place them bottom side up in 

 a shallow tray partly filled with sea water and suddenly pour 

 over them a volume of 6 per cent formalin equal to that of the 

 water in the tray. In the 3 per cent solution of formalin thus 

 made they are to remain at least a week before they are removed 

 to 35 per cent alcohol, and gradually thereafter to 70 per cent 

 alcohol. 



Trachymedusae. — Rhopalonema, Cunina, AEgineta, AEginopsis, 

 Liriope, and Carmarina are fixed in the chrom-osmic liquid for 

 five to twenty minutes, according to their size, washed in fresh 

 water, and gradually transferred to alcohol. Cunina is better 

 when killed with concentrated acetic acid before being hardened 

 with the chrom-osmic mixture. A simpler method for Carmarina is 

 to use formalin of 4 per cnet and chromic acid in equal parts for 

 killing and hardening. Allow the specimens to remain in this 

 mixture from one to two hours; then wash in fresh water and trans- 

 fer to alcohol. 



To prevent the flattening of the bell of Carmarina, Tima, 

 and other large forms place a watch glass in the bottom of the 

 jar and rest the bell of the hydromedusa in its concave side. 



Acalephae 



Charybdaea should be killed with the chrom-acetic mixture 

 No. 2 and immediately afterwards treated with chromic acid of one- 

 half of 1 per cent. After a half hour transfer to alcohol, taking 

 care for the proper suspension of the tentacles. 



Nausithoe, the ephyra of Pelagia, and Rhizostoma are killed 

 by pouring into the sea water containing them 3 per cent of a 1 

 per cent solution of osmic acid. When they have just begun to 

 take on a brown tint they should be washed in fresh water and 

 placed in 35 per cent alcohol. Formalin of 4 per cent may be 

 used with excellent results with these animals, because it does 

 not give the brown tint which is imparted by osmic acid. To 

 avoid the flattening of the umbrella of Rhizostoma, the animal 

 is killed in an exhibition jar with a somewhat narrow neck. After 

 the transfer to weak alcohol the mouth of the jar should be cover- 

 ed with a piece of bladder and should stand upside down, with the 

 convex part of the bell resting in the neck. The medusa should 

 remain in this position until the alcohol has been changed to 70 

 per cent and the whole body has become permeated with the fluid. 

 When formalin is used for killing and hardening, this inverted 

 position should be maintained from the first. 



I Pelagia noctiluca should remain in the chrom-osmic liquid 

 about an hour, and then be washed and placed in weak alcohol. In 

 the alcohol the animal should be suspended by threads tied care- 

 fully to the extremity of each tentacle without tearing it. See 



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