218 NUCLEAR TRANSPLANTATION 



irradiated sperm, host eggs were pricked and the egg nucleus 

 was sucked out in the manner described by Curry (1931, 1936); 

 in my experience, this enucleation technique was successful in 

 only about 50% of the attempts (as determined by the incidence 

 of haploids developing from "enucleated" eggs fertilized by nor- 

 mal sperm). Normal diploid blastula ectoderm and endoderm 

 cells were used for injection and they gave similar results. About 

 65% of the injected eggs cleaved and, of these, about one-third 

 developed into blastulae which externally appeared to be quite 

 normal; however, internally they were invariably atypical and at 

 best had a reduced blastocoele. Most of the cases were sacrificed 

 at the blastula stage for cytological study but, of those permitted 

 to continue development, none progressed beyond the earliest 

 crescent blastopore stage. Since half of these embryos probably 

 retained the egg nucleus after unsuccessful attempts at enuclea- 

 tion and should develop as typical hybrids, these results suggest 

 that the Triton cytoplasm is less able to recover from the injury of 

 injection than is the cytoplasm of R. pipiens. 



The interpretation of evidence from nuclear transplantation in 

 Triton (Waddington and Pantelouris, 1953; Lehman, 1955) is 

 extremely problematical since no development was obtained in 

 these embryos which cannot be duplicated in totally enucleate 

 eggs of this species ( Fankhauser, 1929, 1934 ) . The injected nuclei 

 from undetermined or determined cells from blastula to neurula 

 stages are probably capable of at least limited participation in 

 cleavage and blastulation, but there is no direct evidence that 

 these Triton nuclei can take part in postblastula development. 

 Whether this is due to operative damage or nuclear specialization 

 is not known. Similar types of arrested blastulae have been de- 

 scribed in various salamander hybrids (e.g., Baltzer et al., 1939; 

 Baltzer and Schonmann, 1951), and in certain instances the indi- 

 vidual tissues have been shown to be completely viable when 

 transplanted to normal diploid hosts. The application of this 

 method to the arrested "injection blastulae" of Triton is the most 

 promising approach available at present for assaying the develop- 

 mental capacities of transplanted nuclei of different age and de- 



