276 EMBRYOLOGICAL METHODS. 



method is that described by WHITMAN (Amer. Natural, xxii, 1888, 

 p. 857), and by BLOCHMANN (Zoo/. Anz., 1889, p. 269). WHITMAN 

 puts the fixed eggs into a 10 per cent, solution of sodium hypo- 

 chlorite diluted with 5 to 6 volumes of water, and leaves them there 

 till they can be shaken free, which happens (for Necturus) in a 

 few minutes. BLOCHMANN takes eau de Javelle (potassium hypo- 

 chlorite), and dilutes it with 3 to 4 volumes of water, and agitates 

 the eggs previously fixed with solution of Flemming, -for fifteen to 

 thirty minutes in it. 



LEBRUN (La Cellule, xix, 1902, p. 316) advises fixing ova of Anura 

 for not less than one and a half hours in liquid of Gilson, 69. 

 The outer envelopes are then hard, and may be easily incised and 

 the ovum extracted by pressing on the pole opposite to the incision. 

 The operation should not be delayed until after hardening in alcohol. 

 Similarly (ibid., xx, 1902, p. 12) for Urodela. 



GUYER (Amer. Nat., xli, 1907, p. 400) finds it suffice to roll the 

 ova (either fresh or fixed, but before bringing into alcohol) on 

 blotting paper. 



602. Imbedding. A great difficulty with the ova of Amphibia 

 lies in their becoming extremely brittle on imbedding in paraffin. 

 CARNOY and LEBRUN (La Cellule, xii, 1897, p. 212) fix ovaries or 

 ovarian ova for fifteen minutes to three-quarters of an hour (but 

 see last ) in Gilson's mercuro-nitric fluid, 69, and preserve them 

 in 80 per cent, alcohol. To imbed, they are brought for a quarter 

 of an hour into 95 per 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 

 five 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 chloroform can be added 

 without the mixture becoming turbid, and a second bath of clean 

 paraffin should be added. 



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



603. Siredon. The ova are easier to prepare than those of the 

 Anura, because the yolk is separated from the albuminous 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 



