300 CHAPTER XXV. 



NICOLAS (Arch. Anat. Hie.., 1900, p. 457) finds the best 

 fixative for ova of the slow-worm, as for other large ova, is 

 BOLTINGS picro-formol ( 110). 



See also PKRENYI, 48, and Zool. Anz. } 1888, pp. 139 and 

 196, and other methods in early editions. 



Amphibia. 



602. Preliminary. In order to prepare ova for section- 

 cutting, it is essential to begin by removing their thick coats 

 of albumen. This may be done by putting them for two or 

 three days into 1 per cent, solution of chromic acid, and 

 shaking well ; but ova thus treated are very brittle, and do 

 not afford good sections. A better method is that described 

 by WHITMAN (Amer. Natural., xxii, 1888, p. 857.), and by 

 BLOCHMANN (Zool. Am., 1889, p. 269). WHITMAN puts the 

 fixed eggs into a 10 per cent, solution of sodium hypochlorite 

 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 (potas- 

 sium hypochlorite), 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. See also 589. 



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

 of Anura for not less than 1| hours in liquid of Gilsor., 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. 



603. Imbedding. A great difficulty with the ova of Am- 

 phibia lies in their becoming extremely brittle on imbedding 

 in paraffin. CAKNOY 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 



