ENDOMIXIS IN PARAMAECIUM AURELIA 43 



which was only slightly less than the average in line II, while be- 

 tween the latter endomixis and the next one in line VIII (5/2) there 

 were only seven generations. 



On 3/4 a second line Villa was branched off from VIII and carried 

 in the same culture without change of slide until its death on 3/30. 

 During this time it passed through twenty generations and two periods 

 of endomixis (3/7 and 3/21) with intervening periods of only thirteen 

 and ten generations between the appearance of the last endomixis in 

 line VIII and the first in line Villa, and between the two occurrences 

 of endomixis in the latter line, or an average of eleven and one-half. 

 Why frequency of endomixis should have been increased by the use 

 of this culture is not clear. Approximate bacterial counts showed large 

 numbers of bacteria present, so that the cause was probably not lack 

 of food. The Paramaecia growing in the culture itself and those on 

 the culture slides were rather small and did not show the prominent 

 food vacuoles usually present in healthy animals. It is more likety 

 that poisons of some sort inhibited active growth and prevented the 

 animals from using the food present. Whatever the explanation it is 

 evident that conditions inhibiting growth induced endomixis. It is 

 also worthy of note that initially the culture did not have so pronounced 

 an effect as finally, the frequency of endomixis being increased in line 

 VIII from thirty at the beginning to seven generations at the end of 

 the experiment, and in line Villa from thirteen at the beginning to ten 

 at the end. 



Experiment 9 (figs. IX, IXa and b) 



On 5/6 line IX was branched off from line II and carried with 

 occasional slide changes until 5/14 when it was transferred to a fresh 

 slide and carried until 6/19 with daily slide changes. Endomixis 

 occurred on 5/8 9 and none thereafter for eighty-four generations until 

 the death of the line on 6/19. On 6/1 two lines (IXa and b) were 

 branched off from IX and carried until 6/19 in an old culture, with 

 endomixis ensuing on 6/3 10 forty-five generations after its last occur- 

 rence in line IX and only one generation after IXa and b were branched 

 off from the latter. 



Another line of experiment consisted in using distilled water 

 as the experimental agent, while beef extract was used as the 

 control. The distilled water used in these experiments was 



9 No division occurred on 5/8, while my notes are uncertain regarding the 

 nuclear condition on 5/9. The form of the curve however, and the existence of 

 multinuclearity on 5/10 are sufficient evidence for believing that endomixis 

 occurred on 5/8. 



10 Since IXb he did not divide on 6/3 it is of course impossible to be certain 

 that endomixis occurred in that line on that date. On 6/4 the macronucleus had 

 reformed however, so that there can be no reasonable doubt of this fact. 



