Diversity Produced by Conjugation 161 



There is evidence also that conjugation causes hered- 

 itary differentations to appear with respect to size, but 

 this matter has not been so precisely studied as it deserves 

 to be. 



Calkins and Gregory (1913) observed similar hereditary 

 variations in fission rate and vitality arising after con- 

 jugating. They give some evidence that hereditarily differ- 

 ent families may arise from the first two divisions of one 

 of the members of a pair. During conjugation, as we have 

 seen, new macronuclei are produced from the reserve, micro- 

 nucleus (see Figure 30). The first four of these are pro- 

 duced within the individual that has conjugated, and be- 

 fore reproduction takes place. Then by two divisions these 

 are distributed to the four progeny. According to the re- 

 sults of Calkins and Gregory, the four individuals receiving 

 the four macronuclei thus produced may become diverse; 

 probably, it would seem, through the diversity of these four 

 nuclei. In later divisions such diversities do not appear, 

 according to their account ; at least they say that each of 

 the lines produced remains "true to its type for many 

 months at least." I believe that this matter requires 

 further study, but according to the results of Calkins and 

 Gregory, these inherited differences are strictly the result of 

 conjugation, just as are those shown in my own work. 



We find therefore that in all the hereditary characters in 

 which the matter has been studied, conjugation gives rise to 

 inherited differences ; in other words, diverse stocks arise 

 as a result of conjugation. Such work needs to be greatly 

 extended; all we know on the matter is based on Chlamydo- 

 monas and Paramecium, mainly the latter, and its characters 

 are not so favorable for such work as might perhaps be 

 found. But such work is extremely difficult. 5 



"Certain work of Mast (1917), bearing on this point, in the infu- 

 sorian Didinium, will be taken up in our next lecture. 



