442 METHOD OF CHORIO-ALLANTOIC GRAFTING 



5. Recovery of the graft: 



a. The graft must be removed before the host extra-embryonic membranes 

 begin to dry up. This is generally by the 18th day of incubation, or about 9 

 to 1 days after the transplantation of the graft is made. 



b. Candle the host to attempt to locate the graft. This is generally difficult be- 

 cause of the opacity of the host. However, if the graft has "taken" it will be 

 found close to the original window. Make a cut through the shell about 1 cen- 

 timeter outside of the original window, and remove the shell carefully, with- 

 out rupturing the underlying chorio-allantois. Examine the underside of the 

 shell to see if the explant may be adherent to it. The graft will generally 

 appear as a fluid-filled vesicle, opaque, and without discernible structure. 

 Particularly in the case of the appendage anlage', the detailed structure will 

 not be seen until the tissues are histologically cleared. 



c. Use the Lundvall technique (see above) for quick staining of cartilage, etc. of 

 differentiated limbs. The eyes should be sectioned after normal fixation 

 (Bouin or Kleinberg's) and stained with Conklin's Haematoxylin. 



6. Other embryonic areas to be tested by chorio-allantoic grafting: It is suggested 

 that the following additional structures be given the opportunity to develop on the 

 chorio-allantois. 



a. Anterior half of the primitive streak, including Hensen's node. 



b. Neural crests and nerve cord, from embryos with 3 to 1 somites. 



c. Somite blocks. 



d. Heart anlage' of 42 hour stage. 



e. The entire blastoderm of primitive streak stage. 



(Note: For further instructions the student is advised to consult Hamburger's: 

 "A Manual of Experimental Embryology") 



"The hen does not produce the egg, but the egg produces 

 the hen and also other hens . . . We know that the child comes 

 from the germ cells and not from the highly differentiated body 

 of the parents, and furthermore , that these cells are not made 

 by the parents' bodies but these cells have arisen by the division 

 of antecedent germ cells .... Parents do not transmit their 

 characters to their offspring, but these germ cells in the course 

 of long development give rise to adult characters similar to 

 those of the parent. " 



E. G. Conk I in 



