444 INTRA -EMBRYONIC TRANSPLANTATIONS 



8. Allow the host to continue development for about 9 days, and recover the trans- 

 plant at about 12 days of incubation of the host. The recovery may be difficult 

 since the transplant may be hidden by some of the host tissues, and it may re- 

 quire an exploratory dissection of the host. 



9. Make drawings, gross and histological analysis of the development of the trans- 

 plant. 



Limb primorida grafted into the flank: (See Hamburger, 1938, 1939) 



1. Follow the preliminary directions of the preceding exercise. 



2. Preparation of the transplant: When excising the limb buds leave extensions of 

 tissue from both the anterior and the posterior limits of the bud. These will be 

 used to tuck the bud into the slit. 



3. Preparation of the host: Make a longitudinal slit between the wing and leg bud of 

 the 3-day host embryo. The slit should be no longer than the actual bud, and 

 should be close to the somites so that during growth it may pick up some of the 

 developing muscles. Avoid hemorrhages. 



4. Implantation: Drop the bud onto the host embryo in the vicinity of the slit, and 

 work the anterior end into the slit by means of a (sterile) glass needle. Then 

 work the posterior end into the slit and, finally, using a blunter needle, force 

 the bud itself into the slit leaving the bulge of the bud exposed. It may be neces- 

 sary to lengthen the slit slightly during this process. The slit will close suffi- 

 ciently to hold the bud in place. It must not be allowed to slip into the coelom. 



5. Gently transfer the host egg (after sealing, etc. ), without jarring, to the incuba- 

 tor and leave undisturbed for 48 hours. 



Eye primordia grafted into the flank region: (See Gayer, 1942) 



1. Prepare hosts of about 60 to 72 hours incubation and donors of about 30 to 36 

 hours of incubation. Donor should have from 10 to 12 somites. 



2. With Neutral Red or Nile Blue Sulphate agar stain the right wing bud of the host. 



3. Quickly dissect out the right optic vesicle of the donor (in sterile, chick Ringer's) 

 by making a transverse cut at the level of the infundibulum (just behind the optic 

 vesicle) and then a median cut anteriorly. The piece will include the entire right 

 side of the prosencephalon. (The left side may be used for a second host. ) 



4. Make a longitudinal slit at the base of the wing bud of the 72 hour host, at about 

 the level of the 20th somite. 



5. Drop the excised optic cup onto the host embryo, in a minimum of sterile me- 

 dium, and with the tip of a glass needle (not too sharp) tuck the cut surface of 

 the brain into the slit. This will leave the optic vesicle exposed at the surface. 



6. Since the eye is essentially complete by about 10 days of incubation, the host 

 may be sacrificed at that time and the transplant recovered. It should be com- 

 pared with the eye at the donor age, the eye of any 10-day incubated embryo, 

 and the eye of the hatching chick. The graft may be fixed in Kleinberg's (or 

 Bouin's), dehydrated, and cleared in oil of wintergreen for gross study after 

 which it may be sectioned. 



(There is no particular point in carrying the host to hatching although this may 

 be attempted. If successful it would indicate the achievement of a very delicate 

 operation, but generally the eye would be resorbed. ) 



Interspecific transplantation of neural crests : 



The neural crest of vertebrates gives rise, not only to the dorsal root ganglia, and to 

 the sympathetic system, but also the the pigmented cells known as melanophores, wher- 

 ever they are found, (see exercise on "Origin of Amphibian Pigment"). Since their ul- 

 timate location is often far removed from the neural crest, these cells exhibit extensive 

 powers of migration and of proliferative capacity. They are found in the skin of amphibia, 

 the feathers of birds, and in the mesenteries of the body cavity. 



