SOME METHODS FOR LOWER ANIMALS. 487 



873. Medusae : Sections. I am not acquainted with any 

 perfectly 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. Perhaps better results 

 might be obtained by one of the freezing methods given in 

 177 to 180. 



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

 538, have deservedly become classical for the study of the 

 tissues of this group, especially for the study of the nervous 

 system ; for ganglion cells and nerve-fibrils reduce osmic acid 

 quicker than common epithelium cells. Doubtless in many 

 cases the pyrogallic acid reaction, 361, would give enhanced 

 differentiation. 



The isolation of the elements of the macerated tissues is 

 best done by gently tapping the cover-glass (which may be 

 supported on wax feet). This gives far better results than 

 teasing with needles. A camel-hair pencil also sometimes 

 renders good service. 



875. Siphonophora. This group contains some of the most 

 difficult forms to preserve that are to be found in the whole 

 range of the animal kingdom. You have not only to deal 

 with the very great contractility of the zooids, but with the 

 tendency to general disarticulation of the swimming-bells and 

 prehensile polyps. 



The cupric sulphate method of BEDOT (Arch. d. Sci. phys. et 

 nat., Juin, 1889, t. xxi, p. 556), recommended for the prepara- 

 tion of Siphonophora and other delicate pelagic animals, is as 

 follows : A large quantity of 15 to 20 per cent, solution of 

 the salt is suddenly added to the sea water containing 1 the 

 animals. As soon as they are fixed (which happens in a few 

 minutes) a few drops of nitric acid are to be added and mixed 

 in (this is in order to prevent .the formation of precipitates), 

 and the whole is left for four to five hours. The specimens 

 are then to be hardened before bringing them into alcohol. 



