KOWALEWSKY'S METHOD. 269 



are to be stained in the mass, they should be put into borax- 

 carmine for twenty-four hours in the place of the 50 per cent, 

 alcohol. The times of immersion in the various reagents to 

 be strictly observed. 



Pisces. 



571, 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 Salmonidse must be hardened and removed 

 from their envelopes for the study of the external forms of 

 the embryo. 



To this end, the ova 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 succes- 

 sive alcohols. Embryos thus prepared show no deformation, 

 and their histological elements are fairly well preserved. 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 sec- 

 tion 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 Mutter's solution. Open them therein with fine scissors 

 the vitellus, which immediately coagulates on contact 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 is as follows. The ova are fixed in solution 1 

 of Kleinenberg containing 10 per cent, of acetic acid. After 

 ti-M 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 solution of Kleinenberg, and 

 ;nv then brought through alcohol of gradually increasing 

 strength. 



572. Kowalewsky's Method (Zcit. f. iviss. Zool., xliii, 1886, p. 434). 



