TRANSPLANTATIONS 257 



2. Prepare- the host site hy removing a piece of ectoderm and underlying mesoderm from 

 different sites on different emhryos, e.g.^ Just posterior to the normal position 

 of the gill anlage; heneath somites 9 to 12; just posterior to the anterior limb 

 hud; Just anterior to the posterior limb hud; or in the position of the eye. Ex- 

 cavate deeply enough to provide adequate room for a transplant with considerahle 

 thickness. 



5. The gill swelling will be found in a line with the eye but beneath the first 



several somites. Its anterior extremity will be Just posterior to the otic vesi- 

 cle. With operating glass needle and hair loop cut out the entire gill swelling, 

 and Include mesoderm and some of the pharyngeal endoderm. Keeping the piece in- 

 tact, and properly oriented, transfer it on a needle to the prepared site on the 

 host. Further excavate the host site to hold the transplant, and then hold it in 

 place for JO minutes by means of a cover-slip bridge. Eemove the bridge carefully, 

 and clean away any sloughed off cells around the margin of the wound by means of a 

 hair loop. After complete healing transfer to the growing medium. 



Variations in the above procedure not only Include a different site on the host, but 

 isolation of the germ- layer constituents of the anlage to determine (if any) their sepa- 

 rate ability to develop into gills; rotation of the anlage; and xenoplastic transplants 

 between the slow developing species (A. punctatum) and the rapidly developing species 

 (A. tigrinum) . 



Make drawing or photographic records of individual transplants at appropriate inter- 

 vals. 



THE EYE 



The eye is a composite organ made up from brain (neural) ectoderm and head ectoderm 

 (lens). Transplantations may be made at various stages, and of constituent parts, but it 

 is the purpose of this exercise merely to determine to what extent the entire optic vesi- 

 cle and overlying ectoderm can adjust to a new site on the host, a site devoid of the 

 normal second cranial nerve. 



1. Secure embryos ( Anura stage #17 or Urodela stage #25) and place them in the oper- 

 ating Syracuse dish over Permoplast and in depressions, in Standard Solution. The 

 optic vesicle protuberance can be easily located on the right side of fhe head- 

 Prepare one embryo as the host by excavating a hole in the ectoderm and underlying 

 mesoderm in the lateral body wall; Just anterior to the -position of the hind-limb 

 bud; or in the tail bud. 



2. Eemove the entire optic vesicle on the right side of the donor, including a good 

 portion of the diencephalon. With the overlying ectoderm Intact, transfer the en- 

 tire transplant on a needle to the host site and pack it into place with a hair 

 loop, and hold it for 50 minutes with a piece of cover slip. The eye anlage is a 

 rather compact unit and since there is less yolk and mesoderm around it than 

 around other anlagen, it may not adhere so readily to the host site. For this 

 reason the excavated site should be somewhat deeper than the thicknes& of the 

 transplant, and the surrounding ectoderm should be allowed to partially close over 

 the transplant. 



This procedure can be varied in a number of ways. Extra eyes may be transplanted 

 close to the site of the host eye to determine the degree of fusion or interfet-ence; an 

 older anlage may be transplanted to a younger host (the reverse is likely to give negative 

 results); the eye may be so oriented that the optic vesicle faces inward (in which case 

 an extra covering of ectoderm must be provided); and xenoplastic transplants should be 

 attempted, particularly between species of Amblystoma. (See Hewitt, 1955, Jour. Exp. Zool. 

 69:255 for a study of xenoplastic transplants of eye rudiments between various Anura and 

 Amblystoma.) (Some ingenious transplantations, rotations, and regenerations of older, 

 larval eyes, have been made by Stone and Zaur, I9I+O.) (See exercise on 'Eye Field Opera- 

 tions and on Wolffian Begeneration. ) 



As in all transplant experiments, make drawings or photographs immediately after the 

 operation and at appropriate intervals thereafter. Sectioned material at a later stage 

 will answer the question relative to innervation. 



