TOWARD A GENETICS OF STENTOR 319 



effective in alien c\1:oplasm only when the taxonomic relationship 

 may be considered close. Another difference is that in acetabularias 

 both growth and differentiation can occur for some time in the 

 absence of any nucleus, whereas in stentors whatever the nucleus 

 contributes to the cvtoplasm for growth and morphogenesis is not 

 stored or is exceedingly short-lived. 



Following methods devised by Comandon and de Fonbrune 

 (1939b), Danielli and his co-workers have made exchanges of 

 nuclei between Amoeba proteus and discoides (Lorch and DanielU, 

 1950, 1953; DanielU et al., 1955; reviewed to date in DanieUi, 

 1959). In either transfer the enucleated cell of one species recovered 

 its capacit}" for normal pseudopodial locomotion and its sur^ ival 

 was promoted after receiving a nucleus from the other. For the 

 most part these chimeras, as in my experience with stentors, did 

 not survive; but in one instance at least the implantation of a 

 proteus nucleus into discoides cytoplasm did produce a clone which 

 was kept in mass culture for over 8 years. Back transfers showed 

 that both nucleus and C}1:oplasm became altered in the ahen 

 combination, but the proteus nucleus never became functionally 

 or morphologically identical to that of discoides, nor did the 

 discoides cytoplasm become the same as that oi proteus. 



The persisting influence of both the nucleus and the c\toplasm 

 was also evident in such characteristics of the chimeras as nuclear 

 size, form of the pseudopodia, growth rate, and response to 

 antiserum, which in general fell between those expressed by the 

 two species in pure form. These results led Danielli (1958) to 

 emphasize the irreducible importance of the cytoplasm, because 

 it was never completely made over into the type of the nuclear 

 species, and to suggest the reasonable hypothesis that the nucleus 

 of the cell determines the specific types of macromolecules which 

 are svnthesized, while the cytoplasm controls the way in which 

 they are organized into functional units. This conception is 

 certainly indicated by studies of cihates and especially of Stentor. 

 Faihire of regeneration and growth in the absence of the nucleus 

 indicates this organelle to be essential for svnthesis. But the c\-to- 

 plasm, and especially the ectoplasmic pattern, is obviously 

 intimately concerned with guiding nuclear behavior and deter- 

 mining the location, extent, and direction of asymmetry of the 

 developing feeding organelles. 



