498 AUSTIN RALPH MIDDLETON 



Woodruff and Erdmann ('14) show that in Paramecium during 

 vegetative reproduction there are periodical reorganizations of 

 the nucleus, the vegetative macronucleus being replaced by a 

 new portion of the reserve micronucleus. It has been suggested 

 that this new macronucleus may give an altered hereditary con- 

 stitution, so that at each reorganization inherited variations 

 may appear. Are the effects of selection herein described based 

 on such variations occurring thus at the time of reorganization? 



The relatively short time required for producing inherited 

 differences among the progeny of a single individual make it 

 improbable that the variations in Stylonychia are to be accounted 

 for in this way. As we have seen, marked differences appear 

 after ten days of selection, and these are gradually increased in 

 the next ten days, and again in the next, and so on. The per- 

 centage of difference in proportion to the total average fission 

 rate for the 13 consecutive ten-day periods of Experiment 1 are 

 5.41, 10.35, 5.58, 7.62, 23.81, 13.69, 19.20, 21.93, 15.19, 24.71, 

 26.05, 25.35 and 19.23. These percentages for the three con- 

 secutive ten-day periods of Experiment 3 are: 1.99, 4.36 and 

 7.10. Now in Paramecium the interval between reorganizations 

 is about thirty days. If in Stylonychia the interval is of about 

 this length, it would be quite impossible to account on this 

 ground for the cumulative effects of selection occurring within 

 periods much shorter; selection should show sudden effects imme- 

 diately after the reorganization in a given stock, and should then 

 be quite without effect during the intervening periods. Nothing 

 of this sort appears in the records of the present experiments. 



The main interest of this particular matter lies in its bearing 

 on the question whether variations are definite and limited in 

 extent and possible number, as in rigid Mendelian recombina- 

 tions of invariable factors; or whether variations may be of 

 indefinitely many diverse extents and are not limited by a pre- 

 cise numerically definable factorial structure of the germinal 

 material. If the nuclear reorganization described by Woodruff 

 and Erdmann takes place in a definite way, comparable to the 

 known reductions and recombinations in the chromosomal appa- 

 ratus at the formation of the germ cells, then this could not be 



