364 SOME ZOOLOGICAL METHODS. 



centrated solution of sulphate of iron is also an excellent 

 fixing medium. The animals (Convoluta) die in it fully ex- 

 tended. Liquid of Lang was not successful. 



For staining, he recommends either the osmium-carmine 

 stain or impregnation with gold (one-third formic acid, two 

 minutes ; 1 per cent, gold chloride, ten minutes ; 2 per cent, 

 formic acid, two or three days in the dark. It is well to 

 allow an excessive reduction to take place, and then lighten 

 the stain by means of 1 per cent, solution of cyanide of potas- 

 sium). 



BOHMIG, commenting on the above, says that he has obtained 

 very instructive images with Plagiostomidae fixed with sub- 

 limate and stained with osmium-carmine. 



For Dendroccela (Polycladidea) LANG (Fauna 11. Flora d. 

 Golfes v. Neapel, 1884, p. 30) recommends the following 

 procedure : Fix with one of the mixtures, 46, or with hot 

 alcohol. After washing out, stain for eight to fourteen days 

 in picro-carmine, wash with 70 per cent, alcohol until the 

 greater part of the picrin is extracted, stain for from one to 

 fourteen days in borax carmine, and wash out in the usual 

 way with acidulated alcohol. The result is a sharp stain of 

 nuclei by the borax-carmine, a stain of extra-nuclear parts 

 by the picro-carmine, and a slight maceration of the tissues 

 by the prolonged action of the picro-carmine, which serves to 

 make the limits of cells much more evident than they would be 

 otherwise. Mayer's cochineal is useful for the study of glands. 

 Sections made by the paraffin method. 



728. Nemertina. After considerable experience of this 

 difficult group I have to say that I know of no method of 

 fixation that will certainly give good results. My best results 

 have always been obtained with cold saturated sublimate 

 solution, acidified with acetic acid. I have tried most of the 

 energetically hardening fixing agents, such as the osmic and 

 chromic mixtures, and do not recommend them for this 

 group ; for they seem (the chromic mixtures and perchloride 

 of iron in particular) to act as irritants, and provoke such 

 violent muscular contractions that the whole of the tissues 

 are crushed out of shape by them. And, besides, they do 

 not kill as quickly as sublimate. 



I have found it a good plan to decapitate the animals (in 



