HEREDITY IN THE PROTOZOA 303 



favorable to the view that the differences observed 

 are in reahty failures or imperfections in the 

 processes taking place at this critical period. 



This discussion is based on the assumption that 

 reduction occurs after separation. If on the other 

 hand, reduction of the chromosome number has 

 taken place in the two parental individuals in the 

 division immediately prior to interchange of micro- 

 nuclei, then the two daughter individuals after 

 interchange might be supposed to contain different 

 hereditary complexes, but unless some further re- 

 duction takes place the four granddaughters from 

 each ex-con jugant would be expected to give identi- 

 cal lines. In that case the evidence mentioned 

 above would appear to prove too much, for only two 

 different combinations are expected, not four or 

 eight. 



Something like reduction must occur somewhere 

 if the chromosomes have the same values as in 

 higher forms, for, if not, their number would steadil}^ 

 increase. An obvious objection to the hypothesis 

 that the reduction occurs immediately after conju- 

 gation, is that it is purely specidative, for nothing 

 peculiar in the division of the two micronuclei after 

 conjugation has been observed. The divisions 

 appear like ordinary divisions. Evidence as lo 

 whether the last nuclear division just before conju- 

 gation is reductional, or not, ought to be o])tained 

 from the history of so-called s])lit-pairs. Jennings 

 separated in many cases two individuals of the same 

 line that were about to conjugate and reconhMl 



