340 CHAPTER XXVI. 



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 one drop 

 of concentrated solution of Orange Gr for each 5 c.c., which 

 stains the yolk. 



596. VIALLETON'S Method (Anat. Anzeig., vii, 1892, pp. 624627; 

 Journ. Roy. Mic. Soc., 1892, p. 889). Egg opened in salt solution, blasto- 

 derm 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. 



597. 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. 



Reptilia. 



598. 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 

 with fixatives, etc. 



599. Special Cases. MITSUKURI (Journ. Coll. Sc. Japan, vi, 

 1894, p. 229) fixes embryos of tortoises chiefly with picro- 

 sulphuric acid. To study the blastoderm he removes the 

 whole of the shell and as much as possible of the albumen, 

 marks the place where the blastoderm lies with a hair, 

 brings the whole, with the blastoderm uppermost, into the 

 fixative, and after a few hours cuts out the blastoderm and 

 further hardens it by itself. Young embryos generally 

 adhere to the shell and can, therefore, be fixed in a piece of 

 it made to serve as a watch glass, then after half an hour 

 can be removed from it and further hardened alone. If the 



