LIMB F lELD OPERATIONS 28l 



RELATION OF ECTODERM AN[) MESODERM IN LIM3 FORMATION 



The experimenta on regeneration (atove) throw some light on the relationship of limb 

 hud ectoderm and mesoderm to normal limh development. Since mesoderm alone cannot he 

 grafted, it is necessary first to transplant ectoderm to which the foreign mesoderm at- 

 taches, and then to make a second transplantation, carrying along together the normally 

 unrelated ectoderm and mesoderm, 



a. Transplant the ectoderm alone from area "B" (see diagram) to the region "X" on 

 a second embryo. The transplant should he exclusively ectoderm. I.e., all 

 original mesoderm must he cleaned away with a hair loop. Within 2k hours the 

 graft should he completely healed. Prepare another host by removing the entire 

 limh anlage', ecto- and mesoderm of area "X" of the previously operated emhryo. 

 This consists of original limh ectoderm plus flank mesoderm. Note carefully the 

 exact stage of development of all embryos used; the size of the donor tissue; 

 size of the host area; and the extent of the excision of mesoderm. Should this 

 operation produce a perfectly normal limh It would indicate that the limb disc 

 ectoderm is of prime and exclusive importance, in the development of the limb. 



b. Place flank ectoderm over limb-disc mesoderm, making certain that all flank 

 mesoderm has been cleaned off of the transplant. Should a normal limb develop 

 from this operation, it would suggest the importance of the limb disc mesoderm 

 and the lability of the flank ectoderm. 



c. Transplant flank ectoderm only over limb disc mesoderm for 2k hours, until 

 thoroughly healed. Then excise and transplant the entire disc material (ecto- 

 and mesoderm) to the flank region of another host. In this case the limb disc 

 mesoderm alone is being transplanted to a foreign region. Should a normal limb 

 develop, this would confirm the importance of the mesoderm in limb development. 



These heterotopic transplants are more graphic if they are made between A. punctatum 

 and A. tlgrinum (Harrison, 1955) and at stage #29 and #55- 



EECORD THE RESULTS OF THESE TRANSPLANTATIONS 



