6 THOS. H, MONTGOMERY, 



given somewhat in detail, since the study of the delicate connective 

 tissue elements presents many technical difficulties. And as far as 

 my experience goes, it may be safely said, that methods which are 

 satisfactory for these elements, which are especially difficult to pre- 

 pare, may also be applied with advantage to the study of other histo- 

 logical structures. 



The best fixative for Nemerteans is corrosive sublimate; this is 

 best used in a cone, aqueous solution, warmed to 40° C, for the smaller 

 species ; and in a 50 °/o alcoholic solution, used cold, for the larger 

 forms; sublimate fixes the freshwater species better than the marine 

 forms. Hermann's fluid (platinic chloride + acetic acid + osmic 

 acid) is a better fixative than the preceding for nuclear details, but 

 as it does not penetrate rapidly, can only be used for the smaller 

 species, which may remain in the fluid 20 minutes ; a disadvantage 

 of the fluid of Hermann, is the fact that but few differentiating stains 

 can be used after it. Flemming's mixture (chromo-aceto-osmic acid) 

 does not fix as well as the preceding, but owing to its more rapid 

 penetration, is better adapted for the larger forms; worms may re- 

 main in the stronger fluid recommended by Flemming (in : Z. wiss. 

 Mikr., 1884, p. 349), from 10 to 25 minutes, according to size. 

 Perenyi's fluid (chromo- nitric acid) is good for the preservation of 

 fibrous elements, cell walls, cilia etc., but causes distortion of softer 

 structures, and renders the application of stains difficult. These four 

 methods of preservation are indispensable for the study of cytological 

 details ; and it is more important to use a number of different fixa- 

 tives, than to use a single fixative, followed by various stains. The 

 addition of acetic acid, stronger than 2 7oî to corrosive sublimate, 

 causes an abnormal turgescence of the softer structures, and is to 

 be avoided on this account. Chromic acid in aqueous solutions pro- 

 duces excessive vacuolisation of the more delicate cell structures, and 

 after its use, haematoxylin and carmine stains produce unsatisfactory 

 results ; further, the following preservatives are to be avoided : abso- 

 lute alcohol, picric acid (both aqueous and alcoholic solutions) and 

 Kleinenberg's fluid (picrosulphuric acid). It is very probable that 

 the mixture, corrosive sublimate + acetic acid + osmic acid, as used 

 to good effect by Böhmig for Rhodope ('93) and Rhabdocoelida, could 

 also be applied to the preservation of Nemerteans. 



The stains to be recommended, depend entirely upon the nature 

 of the elements to be studied ; for the connective tissues I have found 

 the following the most satisfactory, to be applied to sections: 



