216 The Nature of Biological Diversity 



Preer (1959), Maly (1958, 1960), Sonneborn (unpublished), and 

 Hanson (1962) have indeed found in Paramecium genie or nuclear 

 differences that determine differences in visible cortical structures or 

 in their morphogenetic processes. These findings have to be accom- 

 modated in reasonable speculations about the decisive determinative 

 molecular organization of the cortex and the modalities of its action. 



Perhaps the main clue — aside from the demonstrated fact that the 

 cortex is essential and determinative — lies in information bearing on 

 the limits of nuclear action. It should be obvious, but commonly is 

 not recognized as such, that the nucleus alone cannot make its corre- 

 sponding cell or any cell at all (Sonneborn, 1951) . This is not merely 

 because the rest of the cell provides a limiting membrane with the 

 function of regulating ingress and egress of materials, for there are 

 regionally diverse decisive areas in the cortex of a single cell. The 

 decisive contribution of the cell cortex is thus its specific organization. 

 Specificity of cytoplasm is correlated with that of the nucleus, for 

 chromosomes in the cytoplasm of a closely related species often can- 

 not function normally and are injured or destroyed (Levine, 1953; 

 Hennon, 1962) . This implies that there must be, for cellular existence, 

 a delicate correlation between genotype and plasmatype which is 

 lethally disrupted by relatively minor changes in either and which 

 slowly co-evolves (see above). This intricate intracellular coordina- 

 tion, the result of ruthless long selection, offers little hope that man 

 could ever devise a noncellular milieu in which a nucleus could oper- 

 ate so as to make its own cell or any cell at all. 



These considerations leave but few sorts of speculative possibilities 

 for the mode of operation of the cortex. On the one hand, the diverse 

 parts of the cortex might be the seat of production of certain mol- 

 ecules not directly or indirectly producible by the action of genes 

 (and food) alone. However, there is at present, so far as I am aware, 

 no evidence for the production by cells of specific molecules inde- 

 pendently of those taken in as food or formed directly or indirectly 

 by genie action. On the other hand, the diverse parts of the cortex 

 (and other preformed cytoplasmic structures) might be the seat of 

 specific absorption and orientation of molecules derived from the 

 milieu and genie action. This alternative is more in harmony with 

 present knowledge. Preexisting cortical structure would then play its 

 essential part by determining where some gene products go in the cell, 

 how these combine and orient, and what they do (Sonneborn, 1951; 

 Tartar, 1961). Apparently such specific assemblies could confer new 

 properties upon molecular groupings. A contemporary example of 

 such origin of new properties appears to be provided by transfer 



