EMBRYOLOGY 377 



With a strip of paper 5 mm. wide and 50 mm. long you construct 

 a sort of triangular bottomless box. You lay this on the yolk, 

 enclosing the cicatricula in such a position that the base of the 

 triangle corresponds to what will be the anterior region of the 

 embryo, and its apex to the posterior 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 preparation 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 

 encloses the cicatricula and marks its position ; you cut out this 

 area with scissors and a scalpel, and complete the hardening with 

 chromic acid and alcohol. 



See also the method of Hirota, Journ. Roy. Mic. Soc, 1895, 

 p. 118. 



819. Kionka's Orientation Method {Anat. Hcfte, 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 hedgehog 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 1 drop of concentration solution of Orange 

 G for each 5 c.c, which stains the yolk. 



820. 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. 



821. Chick and Reptile Blastoderms. Gerhardt {Anat. Anz., 

 xx) uses : — 



Leave in twenty-four hours. Wash twenty-four hours in running 

 water, upgrade from 70 per cent, alcohol, 90 per cent, with iodine, 

 pure 90 per cent., etc. Recommended by Prof. J. P. Hill. 



