454 CHAPTER. XXXVI. 



864. Mucus Glands.— Racovitza {Arch. Zool. ea-fer. [3], ii, 

 1894, p. 8) studies these in Nudibranchs (and Annelids) by 

 Idlling with acetic acid, staining in toto with methyl green 

 dissolved in liquid of Ripart and Petit, and after three to 

 six days, when only the glands show the stain, examining in 

 mixture of equal parts of glycerin and the liquid. 



Arthropoda. 



865. General Methods for Anthropoda. — As general methods 

 for the study of chitinous structures, the methods worked out 

 by Paul Mayer (see §§ 8 and 96) are excellent. It is, at all 

 events, absolutely necessary, in the preparation of entire 

 organisms or unopened organs, that all processes of fixation, 

 washing and staining should be done with fluids possessing 

 great penetrating power. Hence picric acid combinations 

 should in general be used for fixing, and alcoholic fluids for 

 washing and staining. Concentrated picro-sulphuric acid (or 

 picro-nitric) is the most generally useful fixative, and 70 per 

 cent, alcohol is the most useful strength for washing out. 

 Alcoholic picro-sulphuric acid may be indicated for fixing in 

 some cases. 



But if the animals or organs can first be properly opened, 

 the usual methods may be employed. 



866. Crustacea. — Some forms are very satisfactorily fixed 

 with sublimate. Such are the-Copepoda and the larvEe of 

 Decapoda. It is sometimes indicated to use the sublimate 

 in alcoholic solution. Some Copepoda, however {Copilia, 

 Sapphirina), are better preserved by means of weak osmic 

 acid, and so are the Ostracoda. In many cases the osmic 

 acid will produce a sufficient differentiation of the tissues, so 

 that further staining may be dispensed with; so for Copilia 

 and FhyUoscn.a. Q'he pyrogallic process (§ 874) may be useful. 

 GriESBEECHT takes for marine Copepods a concentrated solution 

 of picric acid in sea water, to which a little osmic and acetic 

 acid may be added. For fresh-water forms, Zachaeias [Zool. 

 Anz., xxii, 1899, p. 72) takes chromo-acetic acid. 



GiESBEECHT fixes larvEe of Stomatopoda for 5 to 10 minutes 

 in formol of 10 per cent, warmed to 40° or 50° 0., opens 

 them in sea water and puts for \\ to 2| hours into formol 1 



