296 CHAPTER XXV. 



A description of further developments of this method, with figures of 

 special apparatus, will be found in Ancd. Anz., ii, 1887, pp. 583, 609. 



See also PATON, Juurn. Exper. Zool., xi, 1911, p. 469 (cultivation of the 

 embryo in vitro). 



595. Preparation. During the first twenty-four hours of 

 incubation it is extremely difficult to separate the blastoderm 

 from the yolk, and they should be fixed and hardened to- 

 gether.* In later stages, when the embryo is conspicuous,, 

 the blastoderm can easily be separated from the yolk, which 

 is very advantageous. To open the egg, lay it on its side 

 and break the shell at the broad end by means of a sharp 

 rap ; then carefully remove the shell bit by bit by breaking 

 it away with forceps, working away from the broad end until 

 the blastoderm is exposed. The egg should be opened in 

 salt solution, then lifted up a little, so as to have the blasto- 

 derm above the surface of the liquid ; the blastoderm is 

 then treated with some fixing solution dropped on it from a 

 pipette (1 per cent, solution of osmic acid, or Ranvier and 

 Vignal's osmic acid and alcohol mixture, iodised serum, 

 solution of Kleinenberg, 10 per cent, nitric acid, etc.). By 

 keeping the upper end of the pipette closed, and the lower 

 end in contact with the liquid on the blastoderm, the blasto- 

 derm may be kept well immersed for a few minutes, and 

 should then be found to be sufficiently fixed to be excised. 

 (Of course, if you prefer it, you can open the egg in a bath 

 of any fixing liquid [10 per cent, nitric acid being convenient 

 for this purpose] of such a depth as to cover the yolk ; and 

 having exposed the blastoderm, leave it till fixed [fifteen to 

 twenty minutes] ; but I think the procedure above described 

 will generally be found more convenient.) 



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. 



ANDREWS (Zeit. wiss. Mik., xxi, 1904, p. 177) separates the blasto- 

 derm at this stage by injecting picro-sulphuric acid (not any rapidly 

 acting fixative) firstly between the blastoderm and the vitelline mem- 

 brane, so as to separate the two above, and then between the blastoderm 

 and the yolk, so as to free the blastoderm below and float it up. This 

 done, the membrane may be incised and the blastoderm removed. The 

 injection is best done with a pipette having a fine point bent upwards. 



