CONJUGATION IN BLEPHARISMA UNDULANS 675 



Occurrence and phenomena of conjugation 



0. F. Miiller (1786) described the conjugation of Trichoda 

 aurantiaca and gave a figure that is easily recognized as a spe- 

 cies of Blepharisma. Stein described a number of individuals 

 which he regarded as ex-conjugants, but did not see the con- 

 jugating cells and drew an erroneous conclusion as to the method 

 of fusion of the two individuals. Biitschli (76) was the first 

 to describe the process of conjugation in B. lateritia, making 

 out the method of fusion of the two individuals and the pres- 

 ence of the micronucleus. An interesting feature of this work 

 is that ex-conjugants were unable to live, many individuals 

 dying on the second day after separation, the remainder on 

 the third day. 



Unfortunately I have been unable to study the exogamous 

 conjugation of B. undulans, owing to the failure to find other 

 specimens than those originally isolated. But paedogamous 

 conjugation occurs constantly and the following account refers 

 to that alone. 



All who have carried on careful cultures of protozoa, isolate 

 individual cells each day and transfer them to fresh culture 

 medium, while the remainder are kept together in larger dishes 

 (I use Syracuse watch glasses) and allowed to accumulate in 

 large numbers as 'stock.' Shortly after beginning observations 

 on Blepharisma it was noticed that conjugating individuals were 

 frequent in such stock, amounting in some cases to regular 

 epidemics. No degree of relationship seems too close to pre- 

 vent such union, in one case, for example, an individual was 

 isolated in the 104th generation of the race; it divided during 

 the night and on the following day the two daughter cells were 

 firmly united in conjugation. This, I believe, is the closest case 

 of paedogamy in ciliated protozoa on record. 



The externals of conjugation of B. lateritia as described by 

 Biitschli agree fully with those of B. undulans. The two indi- 

 viduals unite, first at the anterior tips, as in the case of Para- 

 mecium caudatum, and then fuse along the somewhat spirally 

 running central line of the peristome. Stein's assumption that 



