MEDUSA. 457 



it is also better to keep the specimens separate, even in the 

 alcohol, as, if several are together, it generally happens that 

 their tentacles become entangled. The method is due to 

 S. Lo BIANCO. Oceania conica and Tiara may usefully, 

 according to S. Lo BIANCO, be narcotised with 3 per cent, 

 alcohol in sea water before fixation. Liquid of Kleinenberg, 

 which I have seen much used for the fixation of these and 

 similar forms, is, in my opinion, histologically a very objec- 

 tionable reagent for the purpose. 



Trachymedusae and Acalephae may be fixed in the usual 

 way in chromic or osmic mixtures. Osmic acid may conve- 

 niently in some cases be added to the sea water containing 

 the animals, which should be removed to fresh water as soon 

 as they begin to turn brown. 



852. Medusae : Sections. I am not acquainted with any per- 

 fectly satisfactory method of sectioning these extremely 

 watery organisms. Paraffin and collodion will afford good 

 sections of some organs, but are certainly not satisfactory as 

 all-round methods for this group. Some modification of the 

 method employed by the HERTWIGS (Nervensystem der Medusen, 

 1878, p. 5) might be successful. They imbedded in liver 

 with the aid of glycerin gum, and hardened the objects and 

 the mass in alcohol. I should think better results would be 

 obtained by one of the freezing methods given in 315 to 

 320. 



853. Medusae : Maceration. The methods of the HERTWIGS, 

 542, have deservedly become classical for the study of the 

 tissues of this group. 



Amongst other advantages of this process it should be 

 noted that the reduction of osmic acid by albuminates is 

 greatly hastened by the presence of acetic acid, which in the 

 case of animals so transparent and poor in cells as Medusae is 

 an advantage for the study of the nervous system ; for gan- 

 glion-cells and nerve-fibrils reduce osmium quicker than 

 common epithelium-cells. They become greenish brown, and 

 are easily distinguished from surrounding tissues. Doubtless, 

 in many cases the pyrogallic acid reaction, 233, would give 

 better results. 



The isolation of the elements of the macerated tissues is 



