MEDUSA. 373 



and then wash in acetic acid of the same strength till all 

 traces of osmium are removed from the tissues. They are 

 then left to macerate in the acid for a day ; after which they 

 are stained in picro-carmine if the degree of maceration seems 

 sufficient ; if not, in Beale's carmine. Finally, teased prepa- 

 rations are made in glycerin. This method has become 

 classical. 



LIST (Zeit. f. wiss. Mik., iv, 2, 1887, p. 211) recommends 

 dilute liquid of Flemming. Tentacles of Anihea cereus and 

 Sagartia parasitica treated for ten minutes with a mixture of 

 100 c.c. of sea-water with 30 c.c. of Flemming's liquid (the 

 strong solution, 36), then washed out for two or three hours 

 in 0*2 per cent, acetic acid, and teased in dilute glycerin, give 

 fine dissociations of the connective, sensory, and urticant cells 

 of the exoderm, and after removal of the epidermis allow of 

 the demonstration of ganglion-cells and the supporting 

 lamella. Picro-carmine may be used for staining. 



743. Hydroidea, Polypoid Forms : Fixation. In general the 

 polyps may be very well killed in boiling sublimate solution, 

 in which they should be plunged for an instant merely, and 

 be brought into alcohol. Ether attentively administered gives 

 good results with Campanulariadse. Hydra is very easily 

 killed by treatment with a drop of osmic acid on a slide. 

 BRECKENFELD (Amer. Mon. Mic. Journ., 1884, p. 49) obtains 

 good results by heating the animals in a drop of water on a 

 slide for from three to five seconds over a petroleum lamp. 

 The methods for sections are the usual ones. 



744. Medusae : Fixation. There is some difficulty in properly 

 fixing the forms with contractile tentacles, which easily roll 

 up on contac.t with reagents. The best results I have had with 

 these forms have been obtained by means of VAN BENEDEN'S 

 acetic-acid method, 51, followed by alcohol. A similar 

 method, with the difference that a mixture of chromic acid 

 and alcohol is used for washing out instead of pure alcohol, is 

 recommended by DE CASTELLAENAU (La Est. Zool. de Napoles, 

 p. 133) for Oceania, Lizzia, Bouyainvillia, Podocoryne, Syn- 

 coryne, fyc. I have seen good results obtained by etherisa- 

 tion, and also (for large forms) by poisoning with solid corro- 

 sive sublimate added little by little to the water containing 

 the medusae. 



