114 Regulation of Size in Unicellular Organisms 



from each one of the four progeny produced in the 

 second generation after conjugation; this generation 

 marking the completion of segregation in the nuclear 

 materials. Sixteen sub-lines were cultivated, four from 

 each of the four initial progeny; and large numbers 

 of individuals from each of the sixteen lines were fixed 

 for measurement upon each of two separate days. The 

 measurements of length are difficult to evaluate, but 

 it seemed that upon the first of these days the descend- 

 ants of one of the four progeny differed consistently 

 and significantly from those of the remaining three. 

 But in the second set of measurements the difference 

 was not present in at least two of the four sub-lines, 

 of this progeny. The variability due to other condi- 

 tions appears to have been great enough to mask what- 

 ever true genetic differences might have prevailed 

 among these four sets of descendants. 



Biparental inheritance. How is size inherited when 

 individuals conjugate which have distinct size geno- 

 types? This important question remains unanswered, 

 because mating has never been obtained between geno- 

 types which were known to differ (Jennings, '11). Not 

 only does the tendency to assortation discourage the 

 mating of such individuals, but probably other physio- 

 logical differences thus express themselves. All the 

 studies of the effects of conjugation therefore have to 

 do so far as is known with biparental inheritances 

 within a clone. 



Can one demonstrate that inheritance is or is not 

 from both parents, under these conditions? Only in 

 rare instances have differences within a clone been 

 found which are transmitted to offspring. The diver- 

 sities within the limits of "normal variations" are not 

 transmitted for more than three or four generations, 

 at least in ciliates, unless some influence, such as tem- 

 perature change or treatment with a chemical sub- 



