EMBRYOLOGICAL METHODS. 301 



cent, alcohol, five minutes in absolute alcohol, then into a 

 mixture of alcohol and chloroform in equal parts, and as soon 

 as they sink in that they are put into pure chloroform. 

 Paraffin is added to the chloroform, enough to about double 

 the volume of the whole, and the whole is put for about 

 three hours into a stove at 35 C. Lastly, the ova are put 

 for not more than fice minutes into a bath of pure paraffin 

 at 52 C. 



Later (ibid., xix, 1902, p. 317) LEBRUN explains that it is 

 important not to dehydrate completely with -absolute alcohol ; 

 the ova should be left in alcohol of 96 per cent, until chloro- 

 form can be added without the mixture becoming turbid, 

 and a second bath of clean paraffin should be added. 



See also MORGAN, Devel. of the Frog's Egg, New York, 1897, p. 171. 



604. Siredon.- -The ova are easier to prepare than those of 

 the An ura, because the yolk is separated from the albu- 

 minous layer by a wide space filled with a liquid that is not 

 coagulated by reagents. Put the eggs for a few hours into 

 picro-sulphuric acid, then pierce the inner chorion with fine 

 scissors or needles, and gently press out the ovum. Harden 

 in alcohol. 



FICK (Zeif. iciss. ZooL, Ivi, 1893, p. 529) uses a mixture of 

 250 parts of 1 per cent, chromic acid, I of acetic acid, and 

 750 of water. 



605. Triton ( SCOTT and OSBORN, Quart. Journ. Mic. Soc., 

 1879, p. 449). --The albumen is here present in the form of 

 several concentric coats, which are very delicate. Incise 

 each of them separately with fine scissors, turn out the ovum, 

 and fix it in solution of Kleinenberg. 



HERTWIG (Jen. Zeit. Naturw., 18812, p. 291) puts the eggs 

 into a mixture of equal parts of 2 per cent, acetic acid and 

 0'5 per cent, chromic acid. After ten hours he incises the 

 membranes, opening one end of the inner chorion, and turns 

 out the embryos and brings them into successive alcohols. 



MICHAELIS (Arch. mile. Anat., xlviii, 1896, p. 528) fixes ova, 

 with their envelopes, in a mixture of concentrated sublimate 

 solution and concentrated picric acid, twenty parts each, 

 glacial acetic acid 1, and water 40, but removes the envelopes 

 before bringing into alcohol. 



