SPIROSTOMUM AMBIGUUM 413 



the adhesion of many animals by a mucous secretion, and that 

 this condition is particularly prevalent at times of conjugation. 

 Possibly by its means the future conjugants first adhere one 

 to another before any protoplasmic connexion is established. 



Some attempts were made to induce conjugation in the 

 large variety of Spirostomum by experimental means. 



Maupas (19) produced conjugation in S. teres by sub- 

 jecting them to alternations of a rich diet and a period of semi- 

 starvation. A similar process was tried with Spirostomum 

 ambiguum but without any result. 



In his work upon the conditions for conjugation in Para- 

 moecium, Hopkins (11) has produced conjugation by subjecting 

 the animals to a preliminary period of semi-starvation for 

 about two weeks and then adding food and a small percentage 

 of various solutions of inorganic salts. The salt solutions used 

 were : 



0-00002 N solution of ferric chloride, 

 0-00025 N solution of potassium chloride, 

 0-001 N solution of sodium chloride, 

 0-0001-0-0004 N solution of calcium nitrate. 



Somewhat similar experiments have been done by Zweibaum 

 (32). He, too, has been able to produce conjugation, and has 

 found that ferric chloride gives the best results. I was unable, 

 however, to induce conjugation in Spirostomum by any of these 

 methods. Ferric chloride, in the quantities used by Hopkins, 

 was an excellent stimulant to division, and cultures treated in 

 this way gave rise to great numbers of very small Spirostoma,. 

 which, some weeks later, presumably wdien the effects of the 

 salt had been lost, returned gradually to a normal size. 



Conjugation was first observed in the large variety of 

 Spirostomum ambiguum on May 4, 1922. It occurred 

 in a wheat culture which had been kept at a constant tempera- 

 ture of 20° C. since March 13. On May 7 conjugating pairs 

 were observed in two other wheat cultures, both of which had 

 also been kept at the above constant temperature. One 

 culture dated from Januarv 4 and the other from the end of 



