REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 55 



of time (diagram 1). At the 150th generation a sub-culture, des- 

 ignated Sbh, was started from this original culture (diagram 4), 

 and this sub-culture was kept in a hay infusion medium. Both 

 of these cultures thrived until at the 350th generation conjugation 

 occurred in the stock of the Sb culture (beef medium) . Following 

 the occurrence of conjugation in this culture the rate of division of 

 of the main lines rapidly decreased and the culture died out about 

 three weeks later at the 403rd generation (diagram 1). Conjuga- 

 tion did not occur in the Sbh culture (hay medium) and, following 

 the death of the Sb culture, another sub-culture was started by 

 isolation from the Sbh culture (diagram 4) and this culture, desig- 

 nated Sbhb, was placed on the beef medium. This last named 

 culture was continued on the beef medium for about three and one- 

 half months when conjugation occurred in the stock. As in the 

 first beef culture (Sb) the main lines of the Sbhb culture, coinci- 

 dent with the appearance of conjugation, began to decrease in 

 vitality, as indicated by the fission rate, and about three weeks 

 later all the animals of the culture had died (diagram 3). The 

 Sbh culture on the hay infusion continued without conjugation 

 t)ut finally died out at the 572nd generation (diagram 2) . 



IV. MORPHOLOGY AND PHYSIOLOGY OF THE XON-CONJUGANTS 



A. Living material 



In the February epidemic, conjugation made its appearance in 

 the stock of the Sb culture at a time when the animals were divid- 

 ing at the most rapid rate to which they had attained during the 

 entire period of these experiments (diagram 1, point marked X). 

 On account of this fact a slide of three of four days standing would 

 as a rule have a number of animals varying from 100 to 200, and 

 during the epidemic, conjugating animals could always be found 

 on such slides. The phenomenon of conjugation did not occur in 

 the main lines of the culture inasmuch as only a few animals were 

 present on a slide of a day's standing. The point that should 

 be emphasized is that the phenomenon was of very general 

 occurrence on any slide on which were a sufficient number of 

 animals. 



