APPENDIX 



4 



METHODS OF PRESERVATION, ETC. 



For general purposes the eggs and embryos may be pre- 

 served in a saturated solution of picric acid in seventy per cent, 

 alcohol to which a little sulphuric acid has been added (as 

 in Kleinenberg's picro-sulphuric solution). The segmenting 

 eggs or the early stages of the embryo surrounded by the 

 jelly should be put directly into the fluid. Each egg should 

 have, however, the outer jelly-coats cut off with a pair of 

 scissors, and it is well to use an abundance of the preserv- 

 ing solution. Older embryos may be shelled out in the pre- 

 serving fluid with sharp needles. After from three to five 

 hours the eggs or embryos are transferred to seventy per 

 cent, alcohol, which is changed several times ; they should 

 be kept for several days in eighty per cent, alcohol. In 

 this alcohol (eighty per cent.) the inner egg-membrane slowly 

 separates from the egg^ and can be easily removed, after which 

 the egg is preserved permanently in eighty-five per cent, to 

 ninety per cent, alcohol. Corrosive-acetic solution gives good 

 results with older embryos. For the early stages of fertiliza- 

 tion and of extrusion of the polar bodies the following solution 

 is to be recommended : one per cent, chromic acid, twenty-five 

 parts ; water, seventy parts ; glacial acetic acid, five parts. 

 Boiling water also gives good results. 



Difficulty is often found in cutting the eggs on account of 

 the brittleness of the yolk-portion ; but if the following method 

 is carefully followed, there will be no trouble in this regard. 

 The preserved egg or embryo is put into absolute alcohol from 

 two to five hours, turpentine two to three hours, soft paraf- 

 fine a half -hour (change once), hard paraffine a half -hour. 

 The melting-point of the hard paraffine should be from 56 



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