318 H. S. JENNINGS 



comparing these as to vitality, reproductive power, et cetera, 

 with A (which had not conjugated for some months), also with 

 those of branch B (which had conjugated two weeks before). 



The four ex-con jugants of two pairs of C were placed on slides 

 and treated like the non-conjugants of branch A. Two of these 

 ex-conjugants divided once, two did not divide at all, and all 

 died after three to ten days. Meanwhile, the members of branch 

 A multiplied actively, at about the rate of once per day. 



Two other pairs from branch C were allowed to multiply in a 

 watch glass. This they did very slowly, so that on May 13 but 

 10 individuals had been produced from the four. These were 

 then carefully brought into identical conditions with an equal 

 number of specimems of A, and of B, the three being placed side 

 by side in watch glasses. 



On May 16, all the specimens of C were dead, while the mem- 

 iDers of A and B were flourishing. 



Thus in this case, the recent conjugants (C) multiplied very 

 slowly or not at all, and soon died; while others that had not 

 conjugated so recently nor so often (A and B) flourished. 



Ex'peri7nent 11: June 3 to July 28, 1910: Parmnecium aurelia 



Comparison of conjugants and non-conjugants of the branch 

 A (fig. 1, page 307). 



On June 3 there was conjugation in a watch glass (taken from 

 the slides May 15) of members of the branch A (fig. 1), derived 

 from a split pair of March 4. Other divisions of this same stock 

 (branches B and C, fig. 1) had conjugated four times in succes- 

 sion since any conjugation in A. Thus we have in ^ a set that 

 has gone long past the normal conjugation period. Part of it 

 now (June 3) conjugates, while the remainder (part in the watch 

 glass, part on slides) does not. Thus we have an opportunity to 

 test the effects of conjugation on the vitality and reproductive 

 power of a stock that has long gone without it. Experiments 

 for this purpose were conducted on slide cultures, and also in 

 watch glass cultures. 



To make clear the conditions in these experiments (which 

 when described in words alone are a little confusing), I give in 



