H. E. LEHMAN 209 



during development would be by transplantation of a nucleus 

 from a determined cell into one that was labile or totipotent prior 

 to removal of its own nucleus, as, for example, in an enucleated 

 mature egg. Then, as Briggs and King (1952, p. 356) suggest, 

 "the nature of the ensuing development should re\'eal the char- 

 acter of the transplanted nucleus — complete differentiation would 

 indicate that irreversible nuclear differentiation had not occurred, 

 while limited differentiation would indicate that it had." Accord- 

 ingly, when the methods are finally perfected, nuclear transplan- 

 tation gives promise of being one of the most significant technical 

 advances that has been made in recent years for the study of 

 causal relationships between nucleus and cytoplasm and may well 

 rank in importance with hybridization and merogony as an em- 

 bryological tool for protoplasmic recombination. Nuclear trans- 

 plantation has the unique advantage, heretofore impossible, of 

 permitting one to unite a nucleus and cytoplasm of radically dif- 

 ferent age and prospective fate in a manner comparable to that 

 practiced in the standard transplantation of embryonic tissue 

 fragments. 



The first demonstration that nuclear transplantation could be 

 successfully carried out was reported by Comandon and deFon- 

 brune (1939) working with Amoeba sphaeronucleus. A blunt 

 microdissection needle was used to force the nucleus of an intact 

 animal through the cell membrane into an enucleated fragment 

 lying adjacent to the donor animal. The fragment with the trans- 

 planted nucleus, although not regaining its total former metabolic 

 capacity, nevertheless gave evidence of "rejuvenation" after the 

 transfer. Torch and Danielh (1950) and DanielH (1952, 1955) 

 extended the study with homo- and heterospecific nuclear trans- 

 fers between Amoeba proteus and A. discoides. Mass, single clone 

 cultures were very readily obtained from homospecific transfers 

 but were only obtained in about 1% of the nucleocytoplasmic 

 hybrids. Species differences in the parent clones involved nuclear 

 size, body form, mode of locomotion, and specific antigenic char- 

 acters. The nuclear size in hybrids was intemiediate between that 

 of the parent clones, indicating that the cytoplasm exerts some 

 influence in determining this character. The general shape and 



