M. DUVAI/S ORIENTATION METHOD. 265 



and alcohol mixture, iodised serum, solution of Kleinenbe_rg^ 

 10 per cent, nitric acid, &c.). By keeping the upper end of 

 the pipette closed, and the lower end in contact with the 

 liquid on the blastoderm, the blastoderm may be kept well 

 immersed for a few minutes, and should then be found to be 

 sufficiently fixed to be excised. 



The egg is put back into the salt solution, and a circular 

 incision made round the embryonic area. The blastoderm 

 may then be floated out and got into a watch-glass, in which 

 it may be examined, or may be brought into a hardening 

 liquid. 



Before putting it into the hardening fluid, the portion of 

 vitelline membrane that covers the blastoderm should be re- 

 moved with forceps and shaking. 



In order to counteract the turning up of th. 3 edges of the 

 blastoderm that generally happens during the process of hard- 

 ening, it is well to get the blastoderm spread out on the 

 convex surface of a watch-glass, and leave it so during the 

 hardening. 



For hardening, FOSTER and BALPOUR recommend solution of 

 Kleinenberg for five hours, followed by alcohol. Or chromic 

 acid, a solution of 0* 1 per cent, for twenty-four hours, followed 

 by a solution of 0*3 per cent, for twenty-four hours more, 

 then by 70 per cent, alcohol for a day, 90 per cent, alcohol 

 for two days, and lastly absolute alcohol. They also recom- 

 mend a 0'5 per cent, solution of osmic acid, in which the em- 

 bryo remains for two hours and a half in the dark, and after 

 washing is brought into absolute alcohol. 



HENNEGUY prefers the osmic acid and alcohol mixture of 

 Ranvier and Vignal, or Flemming's mixture followed by suc- 

 cessive alcohols. 



Staining and imbedding may be performed by the usual 

 methods. 



Up to about the fiftieth hour embryos may be mounted 

 entire, in glycerin or balsam. 



559. M. Duval's Orientation Method (Ann. d. Sc. nat. Zool, 

 1885). In the early stages of the development of the ova of 

 Aves, before the appearance of the primitive streak, it is 

 difficult to obtain a correct orientation of the hardened cica- 

 tricula, so as to be able to make sections in any desired direc- 



