324 THE BIOLOGY OF STENTOR 



in relation thereto. Pieces of exconjugants did not resorb the old 

 portions of the macronucleus if new nuclear anlagen were not 

 present in them. New macronuclei could support regeneration 

 from the start, but after the first stages of disintegration the old 

 nucleus could not. These conclusions are in line with what is 

 found in other ciliates, and I also have noted that coeruleus which 

 had begun conjugation were unable to regenerate excised oral parts. 



That the proper conditions for conjugation seldom occur was 

 noted in the first extensive study by Hamburger (1908), who 

 remarked that Stentor cultures may be carried on for years without 

 noticing pair-formation. When conjugation does occur only about 

 I to 10% of the animals are involved so that no mass ** epidemics " 

 occur, as in Paramecium. She also found that many isolated single 

 animals from cultures in which conjugation was occurring did not 

 themselves subsequently pair. Her study was therefore of only 55 

 conjugants, the products of which did not live sufficiently long to 

 reveal the complete nuclear transformations. Later, Mulsow 

 obtained material from mixed pond samples which were rich in 

 fauna and flora. They were left unfed in the laboratory and after 

 a week apparently abundant conjugation of coeruleus and poly- 

 morphus present occurred. The experience was repeatable on fresh 

 samples. Bad conditions may have developed in the jars because 

 all the stentors died following the period of conjugation. Possibly 

 a putrid condition developed although he did not say so. At the 

 same time Paramecium and Frontonia present in the samples also 

 conjugated, which would indicate that methods employed for 

 paramecia might be applicable to stentors. However, I have made 

 mixtures of 5 stocks of coeruleus in the hope of providing mating 

 type diversity, and subjected them to feeding and starvation 

 routines to which paramecia are usually responsive, but this first 

 attempt to induce conjugation was entirely unsuccessful. 



Mulsow's (191 3) study included over 2,000 conjugating pairs of 

 coeruleus and a smaller but substantial number of polymorphus 

 conjugants, incidentally confirming many of the points made by 

 his predecessors. He was able to keep his exconjugant animals 

 considerably beyond the period required for completion of all 

 transformations. Sectioned material was studied, for he found that 

 squashed preparations and total amounts were not satisfactory. I 

 have tried to express Mulsow's account of the course of conjugation 



