298 CHAPTER XXV. 



With a strip of paper 5 millimetres wide and 50 millimetres 

 long you construct a sort of triangular bottomless box. You 

 lay this on the yolk, enclosing the cicatricula in such a posi- 

 tion that the base of the triangle corresponds to what will be 

 the anterior region of the embryo, and its apex to the pos- 

 terior region ; that is to say, if the big end of the egg is to 

 your left, the apex of the triangle will point towards you. 

 You now, by means of a pipette, fill the paper triangle with 

 0'3 per cent, solution of osmic acid. As soon as the prepara- 

 tion begins to darken you put the whole egg into weak chromic 

 acid, remove the white, and put the rest into clean chromic 

 acid solution for several days. After hardening you will find 

 on the surface of the yolk a black triangular area, which en- 

 closes the cicatricula and marks its position ; you cut out 

 this area with scissors and a scalpel, and complete the harden- 

 ing with chromic acid and alcohol. 



See also the method of Hi ROTA, Journ. Roy. Mic. Soc., 

 1895, p. 118. 



597. KIONKA'S Orientation Method (Anat. Hejte, 1 Abth., 

 iii, 1894, p. 414). Open the egg under salt solution, free it 

 from the shell and albumen, and mark the poles by sticking 

 into it, at about a centimetre from the blastoderm, two hedge- 

 hog spines, the one at the obtuse end being marked with a 

 red thread. Put the whole for ten minutes into water at 

 90 C., then bring into 70 per cent, alcohol, and after twenty- 

 four hours cut out the blastoderm and a little yolk round it 

 in the shape of an isosceles triangle, whose base marks the 

 anterior end of the blastoderm. Paraffin sections stained 

 with borax-carmine, washed out with acid alcohol containing 

 one drop of concentrated solution of Orange Gr for each 5 c.c., 

 which stains the yolk. 



598. VIALLETON'S Method (Anat. Anz., vii, 1892, p. 624). Egg 

 opened in salt solution, blastoderm excised and removed to a glass plate, 

 then treated with 1 per cent, nitrate of silver solution, washed with 

 water, and put into 70 per cent, alcohol for six to twelve hours in the 

 dark. Borax-carmine, alcohol, damar. 



599. BOHM and OPPEL (Taschenbuch, 1896, p. 80) fix ova with fairly 

 large embryos in a mixture of 20 parts 3 to 5 per cent, nitric acid and 

 1 to 2 parts 1 per cent, silver nitrate. 



