282 THE BIOLOGY OF STENTOR 



with moniliform nuclei. There is apparently a standard pattern 

 for the distribution of nuclear material in all large species. The 

 essential point is that with remarkable constancy the macronucleus 

 tends toward a definite arrangement with reference to the topo- 

 graphy of the cell and that if this pattern is not fulfilled or if 

 artificially disturbed the nodes can and do move in such a way 

 that they tend to recover the normal arrangement. 



The typical disposition of the nuclear beads is shown in Fig. 78A. 

 With the possible exception of a few of the posterior nodes the 

 nucleus is usually entirely subcortical in its location. This is no 

 doubt why it can remain fixed in position; because it adheres to 

 the inside of the ectoplasm. We do not say attached, because one 

 has to allow for the movement of the nucleus during clumping and 

 in the correction of disarrangements. Generally, the longest part 

 of the nucleus is a row of nodes extending almost directly 

 posteriorly under the surface near the meridian which connects 

 the mouth with the posterior pole and considerably to the right 

 of the primordium site. From this row, beads extend around the 

 anterior end of the cell to the right for some distance, while at the 

 other end the row bends back on itself and terminates in several 

 beads which seem to be rather indefinite in their location though 

 they tend to place themselves on the opposite or left side. I think 

 this arrangement is what one would expect if he had to work with a 

 nucleus of minimal length for the sake of economy, to fasten it 

 inside the cell so that it would not "fall to the bottom", have 

 every point in the cytoplasm as close as possible to some nuclear 

 material, and place the nucleus as near as manageable to the most 

 active regions (the membranellar band, the mouthparts, the 

 primordium site, and the holdfast), while keeping it out of the way 

 of the migrating primordium, i.e., to assure that the ectoplasm 

 under which it lies will not undergo major shifts of position. The 

 actual deployment fulfills these assumed requirements. 



Having made these statements, we now have to qualify them by 

 saying that the nucleus is not always in the same position, as well 

 as that its precise location is evidently not essential to the economy 

 of the cell. The first of these qualifications is documented in 

 Fig. 78B, which shows a number of the atypical arrangements 

 which have been found in stentors fished out of regular cultures 

 in which the majority of individuals showed a more normal 



