KMHRYOLOGIOAL METHODS. 303 



BOUIN takes for larva) of Rana the formol-siiblimate 

 mixture 112. 



608. Sulphate of Copper Liquid (FoL, Lehrbnck, p. 106, after 

 REMAK and GOETTE) ; for hardening ova of Amphibia : 



"2 per cent, solution of sulphate of copper . 50 c.c. 



Alcohol of 25 per cent 50 ., 



Rectified wood vinegar 35 drops. 



Pisces. 



609. Teleostea in General. The ova of many of the bony 

 fishes can be studied by transmitted light in the living state; 

 but those of the Salmonida3 must be hardened and removed 

 from their envelopes for the study of the external forms of 

 the embryo. 



To this end they may be put for a few minutes into water 

 containing 1 to 2 per cent, of acetic acid, and thence into 

 1 per cent, chromic acid. After three days the capsule of 

 the ovum may be opened at the side opposite to the embryo, 

 and be removed with fine forceps. The ovum is put for 

 twenty-four hours into distilled water, and then into suc- 

 cessive alcohols. Embryos thus prepared show no deforma- 

 tion, but the vitellus rapidly becomes excessively hard and 

 brittle, so as greatly to interfere with section-cutting. 



The following processes give good results as regards 

 section-cutting. 



Put the ova for a few minutes into 1 per cent, osmic acid ; 

 as soon as they have taken on a light brown colour bring 

 them into Miiller's solution. Open them therein with fine 

 scissors the vitellus, which immediately coagulates on con- 

 tact with air, dissolves, on the contrary, in Miiller's solution 

 and the germ and cortical layer can be extracted from the 

 capsule of the ovum. They should be left in clean Miiller's 

 solution for a few days, then washed with water for twenty- 

 four hours, and brought through successive alcohols. 



Another method (HENNEGUY) is as follows : The ova are 

 fixed in solution of Kleinenberg containing 10 per cent, of 

 acetic acid. After ten minutes they are opened in water 

 containing 10 per cent, of acetic acid, which dissolves the 

 vitellus. The embryos are put for a few hours into pure 



