1^1*8 EXPERIMENTAL CHICK EMBRYOLOGY 



Limb prlmordia grafted Into the flank : (See Hamburger, 1938, 1959) 



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. 



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

 of the 5 -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. 



h. Implantation: Drop the bud onto the host embryo in the vicinity of the silt, 

 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 blxmter needle, 

 force the bud itself into the slit leaving the bulge of the bud exposed. It 

 may be necessary to lengthen the slit slightly during this process. The slit 

 will close sufficiently 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 in- 

 cubator and leave undisturbed for UQ hours. 



Ejye prlmordia grafted into the flank region : (See Gayer, 19^2) 



1. Prepare hosts of about 6o to .72 hours incubation and donors of about 30 to 56 

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



2. With Neutral Eed 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 

 Blnger's) by making a transverse cut at the level of the Infundibulum (just be- 

 hind the optic vesicle) and then a median cut anteriorly. The piece will in- 

 clude the entire right side of the prosencephalon. (The left side may be used 

 for a second host.) 



h. 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 medium, 

 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 ELlnenberg's (or 

 Bouin's), dehydrated, and cleared in oil of wlntergreen 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 to the pigmented cells known as melanophores, wherever 

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

 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. 



Wlllier and Eawles have successfully transplanted neural crests between bird species 



which exhibit radically different color patterns, and some which are white. They found 



that the color pattern, in all cases, was due to the intrinsic genetic factors of the 



specific melanophores concerned, rather than to the feather structure. There was found to 



be some slight modification of pigment expression of the melanophores by the host feather 

 germs. (See Wlllier I9I1I: Amer. Nat. 75:156 for review.) 



