THE CYTOPLASM 



a cytoplasm devoid of kappa, there is no development of Killer; but 

 K, in the way characteristic of nuclear genes, continues to maintain 

 itsclt indefinitely, so that, should conjugation or any other process 

 restore kappa to the cytoplasm, Killer behaviour would once more 

 begin to appear. 



Fig. 42. — The inheritance of the Killer property as shown in certain crosses between 

 strains o{ Panmiccium aurclia by Sonneboni (1947). Witliin the circles is the square 

 Killer gene dominant to its round allelomorph ; outside them is the square cytoplasm 

 with kappa which depends on both the action of the gene in the nucleus and the 

 presence of its prototype plasmagene in the cytoplasm to maintain it (after 

 Darlington, 1944). 



The reproduction of K is independent of kappa, and indeed so 

 far as we know of anything else in which the cytoplasms may differ. 

 The reproduction of kappa is not, however, independent of K, for 

 if iCis replaced by k in the nucleus of an individual whose cytoplasm 

 carries kappa, not only is there a loss of the Killer behaviour, but 

 kappa also disappears after four or five fissions. Evidently kappa 

 cannot reproduce in the absence of K, and so disappears as soon 



176 



