INVERTEBRATES 595 



a weak solution of chloride of ruthenium, especially for nerve- 

 tracts, mucus-cells and cilia. Alcohol material may be macerated 

 in a mixture of 1 j^art glycerin, 2 of acetic acid and 40 of water. 



1179. Mucus Glands. Racovitza {Arch. Zool. Expe'r. {S), ii, 

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

 ing with acetic acid, staining vi 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 



1180. General Methods for Arthropoda. As general methods 

 for the study of chitinous structures, the methods worked out 

 by Paul Mayer (see §§ 102 and 103) 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 alcoliolic 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. 



1181. Crustacea. Some forms are very satisfactorily fixed 

 with sublimate. Such are the Copepoda and the larvae of Dcca- 

 poda. 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 far Copilia and Phyllosoma. The pyrogallic 

 process (§ 413) may be useful. Giesbrecht 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, Zacharias {Zool. Anz., xxii, 1899, p. 72) takes 

 chromo-acetic acid. 



Giesbrecht fixes larvae of Stomatopoda for five to ten minutes 

 in formol of 10 per cent, warmed to 10° or 50° C, opens them 

 in sea-water and puts for one and a half to two and a half hours 

 into formol 1 part and sea-water 5 parts, and brings into alcohol 

 of 70 per cent. 



Staffers {La Cellule, xxv, 1909. p. 356) fixes Sympoda in 

 Gilson's copper formol, § 120, or in Hornell's mixture of 100 

 parts of 5 per cent, formol with 40 of alcohol ; and for softening 



