Genie Control of Development 291 



nucleus is not involved here, the underlying causative chain may be 

 the same as in the former examples.) 



Though in all these cases the cytoplasm clearly controls nuclear 

 behavior, it must be realized, first, that there is no reason to assume 

 that the genie material in the nucleus has been affected, changed, or 

 restrained; second, that the differential protoplasm which affects the 

 behavior of the nuclei has been set aside during oogenesis, most 

 probably under control of the genie material in the nucleus, the proc- 

 ess being of the type of predetermination. Thus it would be wrong to 

 maintain that any of these cases demonstrate nuclear differentiation 

 during development. 



At this point it should be added that some facts show the occa- 

 sional occurrence of what seems to amount to Weismann's erbunglei- 

 che Teilung. In the classic case of Dyticus ( Giardina ) the prospective 

 egg cell retains in four consecutive divisions all the heterochromatin, 

 while the prospective nurse cells, the other products of these divisions, 

 have only euchromatic nuclei (see I 2 C b). Thus the nuclei resulting 

 from these divisions are differently constituted. However, as our 

 analysis showed, this does not mean an erhungleiche division in the 

 sense of our present discussion; though it cannot be denied that a 

 possibility exists that in normal development divisions may occur of 

 the same type, with the same consequences of enhancing or inhibiting 

 future divisions by the control of the quantity of heterochromatin. No 

 such case is known to me, but it would be worth while to check the 

 teloblasts of worms for such an occurrence. 



Another example is the division of the fertilization nucleus (or 

 one of its division products) in Infusoria into a future macro- and 

 micronucleus, known since Biitschli (1876). Sonneborn (1955) has 

 made a remarkable analysis of this phenomenon; the results belong 

 partly to the present discussion and partly to the chapter on cyto- 

 plasmic heredity, where the important points have already been dis- 

 cussed (see II 2 E d hh). It is remarkable that the unequal (in a 

 functional sense) division of the nucleus leads to the establishment of 

 macro- and micronuclei which are definitely different in function and 

 in prospective possibilities, though lying side by side in the same 

 cytoplasm. Nevertheless, both perpetuate indefinitely their character- 

 istics, though originally the macronuclear control of mating type was 

 induced by cytoplasmic specificity (which in turn was under nuclear 

 control). This functional difference of the macronucleus, already said 

 to be self -perpetuating, remains so over subsequent generations. There 

 is, of course, the question whether these interesting features are 



