348 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



for four or five weeks, spending time and care over them, to eventually 

 find, when the "eye-spots" do not develop, that all our trouble was 

 wasted and that no development at all took place. 



It is true one may, with proper preparations and with the help of the 

 pocket-lens or microscope, follow the development while there may be 

 no external signs of the process evident. This method of making the 

 test is, however, not adapted to the purposes of the practical fisk-cult- 

 urist, who will have better success by the following method: 



If fertilized fish ova are placed in a 50 per cent, solution of wine vine- 

 gar [Any ordinary vinegar will probably be found to answer just as 

 well — Tr.J the embryo, even during the very first stages of development, 

 will become apparent to the eye lying on the transparent yelk. The 

 acetic acid contained in the mixture, one part water to one part wine 

 vinegar, causes the material of the embryo proper to coagulate while the 

 yelk remains clear. 



A short time after the ova are laid in this mixture, and during the 

 first week after impregnation, a white circle at one pole of the egg should 

 become apparent, and in the course of the second week a cylindrical 

 white streak running from the edge of the circle towards its center 

 should be evident. If these features are not developed by the test, the 

 eggs have not been fertilized, and are, therefore, worthless. 



We will not complicate the application of the method by describing 

 other details of the development, but would merely suggest that when 

 a lot of ova are fertilized a small portion should be left unimpregnated. 

 These could then be tested in comparison with the fertilized ova from 

 day to day, using say three eggs at a time of each lot. The observant 

 culturist could by this means construct for himself a scale of develop- 

 ment covering the period embraced by his experiments. At a lower 

 temperature the development is slower than at a higher one. The dif- 

 ference of appearance between fertilized and unfertilized ova treated 

 by the method will demonstrate its utility. Whoever does not trust to 

 the method for the evidence of death of the eggs until after five weeks 

 subsequent to impregnation, must of course wait. 



Director Tiefenthaler, of Kolzen, has had the kindness to test the 

 method practically, and finds it useful to fish-culturists. 



[A very little practice, it seems to the translator, would serve to 

 enable any person of ordinary intelligence to apply this method or sev- 

 eral others which might be suggested. Other substances which would 

 answer the same purpose would be dilute solutions of picric or chromic 

 acid, of not more than one to one-half per cent, or one part to two hun- 

 dred of water. Vinegar or acetic acid of the shops may also be used ; 

 the last to be diluted in the proportions of about one part in ten of water. 

 The acids cited will coagulate and cause the germ disk to turn white or 

 yellow in a few hours. Chromic is better than picric acid, as it coagu- 

 lates the yelk also, but turns the latter much darker than the embryo 

 or embryonic disk. — Tr.] 



