274 EMBRYOLOGICAL METHODS. 



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. 



596. KIONKA'S Orientation Method (Anat. Hefte, 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 concentrated solution of Orange^G^for each 5 c.c., which stains 

 the yolk. 



597. 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. 



598. Chick and Reptile Blastoderms. GERHARDT (Anat. Anz., 

 xx) uses : 



Chromic acid 1 per cent. .... 150 c.c. 

 Sat. corr. subl. . . . . . . 150 ,, 



Aq. dest. 135 



Acetic acid . . . . . . 15 



Formalin 150 



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. 



Reptilia. 



599. General Directions. The methods described above for birds 

 are applicable to reptiles. During the early stages the blastoderm 

 should be hardened in situ on the yolk ; later the embryo can be 

 isolated, and treated separately. 



BOHM and OPPEL (Taschenbuch, 1900, p. 186) remove the shell 



