294 H. S. JENNINGS 



by measure, so that it varied in strength from day to day. All 

 the specimens were treated alike at each change, so that no dif- 

 ference between the sets resulted from this; but the changes in 

 concentration of the infusion caused many deaths. (2) The hay 

 of which the infusion was made was not sorted over, to exclude 

 all but Timothy; thus at times injurious plants were included, 

 increasing the mortality. (3) As a rule, only one individual of 

 each line was retained at each change, so that if this individual 

 died, the line became extinct. As a consequence of all these 

 things, the number of lines decreased rapidly in all the different 

 sets. 



However, such an experiment, lasting eight weeks, is not likely 

 to be often repeated, and the results are of much value in certain 

 relations. 



Three sets of the animals were employed in this experiment. 

 One set ('pairs') consisted of individuals that had just conjugated; 

 a second ('split pairs') included individuals that had begun to 

 unite for conjugation, but were separated, in the manner pre- 

 viously described; the third set ('free') consisted of ordinary 

 individuals that had not begun union, taken from the same cul- 

 ture as the others. This third set is known not to have conju- 

 gated recently, since they were taken (like the others) in the 

 early morning, from watch glasses which contained no conju- 

 gants when set the evening before. Comparison of the 'split 

 pairs' and the 'free' will show whether entrance upon the condi- 

 tion preparatory to conjugation alters the animals in any way, 

 such as to affect their multiplication and vigor. 



The 'free' specimens were given paired designations, each two 

 being called a and b, as in the 'pairs' and 'split pairs'. In this 

 case of course a and b were related in no way; the paired desig- 

 nations were given at random, in order to test the question 

 whether one individual of a pair of conjugants dies or is weak 

 more often than occurs as a result of mere chance causes, in 

 specimens paired at random and merely by designation. This 

 is a matter that will be dealt with fully in a later paper. 



The three sets were treated in exactly the same way, the slides 

 of pairs, split pairs and free alternating in the same moist cham- 



