344 S. O. MAST 



in the conjugating group was slightly lower than it was in the 

 non-conjugating group and the death-rate was also somewhat 

 lower. On May 20 all of the dishes containing the didinia 

 belonging to both groups were returned to the damp chamber 

 after removing one specimen from each to continue the lines. In 

 all of the dishes returned the didinia soon became very numerous 

 and two days later conjugation occurred in one dish of each 

 group. Fifteen conjugating pairs (30 individuals) from the 

 non-conjugating group were isolated. Twelve of these indi- 

 viduals died without dividing. . From the remaining individuals, 

 four were selected to start a new group of five lines as repre- 

 sented in the table. During the next ten-day period the rate 

 of fission in these lines, which had just conjugated was somewhat 

 lower than it was in those which had conjugated forty days 

 earlier, but during the following period it was a trifle higher. 

 At the close of this period, June 11, all of the didinia were left 

 in the dishes. They became very numerous and soon consumed 

 all of the paramecia after which many of them encysted. The 

 dishes containing the cysts were then properly labeled, sealed 

 with paraffin and vaseline and stored away in the damp cham- 

 ber. Toward the last of April, 1911, vigorous paramecia cul- 

 tures were added to all of the dishes, and the following day 

 active didinia appeared in one belonging to the more recently 

 conjugating group. None appeared in any of the other dishes. 



TABLE 1 



Effect of conjugation and encystment on fission-rate and death-rate in Didinium 



The large numbers in the columns represent the total average number of 

 fissions in a group of lines for the period given above. The small numbers di- 

 rectly below the large ones indicate the number of lines in the group present 

 at the beginning of the period; wherever these are missing the number of lines 

 in the preceding period has been maintained. The small numbers followed by 

 'd' indicate the number of lines which died out and those followed by 'c' the 

 number which encysted during the period. The brackets and arrows indicate 

 the origin and ancestry of the different groups of lines. Conj., Conj. Sep., small, 

 large, signifies that the numbers following each refer to a group of lines which 

 originated respectively from ex-con jugants, conjugants separated before nuclear 

 transfer occurred, small individuals ready to conjugate, and large individuals not 

 ready to conjugate. CTjst. signifies that the group of lines represented by the 

 preceding numbers were encysted during the period indicated above. 



