H. E. LEHMAN 219 



velopmental history. Although the eggs of Triton appear to be 

 relatively unfavorable for nuclear transplantations, it is hoped 

 that techniques for activation, enucleation, and injection can 

 be improved so that decisive evidence can be obtained concern- 

 ing nuclear differentiation in this classic form for embryonic 

 study. Other species of Triturus (Triton) may be more amenable 

 to nuclear transplantation than T. palmatus, and the search for 

 such a species is particularly desirable in view of the favorable 

 cytological properties of this material. 



The cytological analysis of "nuclear transplant embryos" is 

 deserving of more thorough study. Nothing is known concerning 

 the actual behavior of the injected nuclei during the initial cleav- 

 age stages, and this subject has considerable intrinsic interest 

 entirely apart from the question of determination. Secondly, it is 

 apparent that the major evidence of successful egg enucleation 

 followed by injection of a diploid donor cell is based on the pres- 

 ence of diploid nuclei in tissues of the experimental embryo; 

 haploidity is indicative of failure in enucleation of the egg. In 

 the studies by Briggs and King, ploidy in "nuclear transplant" 

 embryos that developed to late neurulae and tadpole stages was 

 determined by nuclear size and, wherever possible, by nucleolar 

 number (for method, see Briggs, 1947). Of 67 cases reported 

 (Briggs and King, 1952; King and Briggs, 1954a), only one em- 

 bryo gave evidence of failure in enucleation; this was a haploid- 

 diploid mosaic which had been injected with a young gastrula 

 cell. It probably indicates that both the egg and injected nucleus 

 cooperated in development. The remaining 66 cases represent 

 successful enucleation and transplantation; 34 were diploid and 

 32 were polyploid (probably tetraploid). Briggs and King (1952) 

 suggested that the high incidence of polyploidy may result from 

 doubling and division of donor chromosomes before the egg cyto- 

 plasm is capable of cleaving. This is probably true, but it does 

 not relieve the necessity of considering the possible develop- 

 mental significance of polyploidy in the experimental animals. 

 This is particularly important when one examines the data given 

 below and finds that the incidence of polyploid individuals in- 



