336 "H. S. JENNINGS 



of the above three at one of the five periods. But we may hold 

 rigidly to our test and still demonstrate the existence among the 

 conjugants of the three diverse lines 1, 8 and 16. As will be 

 observed, the fission rate is on the average more than twice as 

 great in No. 1 as in No. 16. 



Among the non-conjugants also there are inherited differentia- 

 tions. In every period but one, non-conjugant line 1 has twice 

 as high a fission rate as line 14. On the basis of our severest test, 

 it is clear that lines 1, 12 and 14 are diverse in their inherited 

 rate of fission. 



It is clear therefore that heritable differentiations do arise 

 within the pure line, so far as the rate of fission is concerned. 

 How are these differentiations brought about? 



At this point a weak spot in the plan of the present experiment 

 appears. All our experiments show that conjugation increases 

 the variability in the rate of fission; this is true both in wild cul- 

 tures and in pure lines, and holds for the present experiment, as 

 table 20 shows. It would appear probable therefore that some 

 of these variations are inherited, and that this is precisely what 

 the results given in table 33 demonstrate. But we find inherited 

 differentiations also, as we have seen, among what we have 

 called the non-conjugant lines of the present experiment. The 

 weak point mentioned relates to the applicability of the term 

 'non-conjugant' to these lines. As already set forth, the last 

 previous recorded conjugation took place for this line k on 

 April 29. The present experiment began December 6. Now, 

 it is almost certain that in the intervening time the animals had 

 conjugated one or more times, since this race k conjugates once in 

 one or two months, when conditions are favorable. Therefore, 

 if conjugation produces differentiations, my 'non-conjugants' of 

 the present experiment have had much opportunity to become 

 differentiated in that manner; they are not properly 'non-conju- 

 gants' for present purposes. That they have become in som^ way 

 differentiated is clearly shown by comparison of No. 1 with No. 14 

 in the non-conjugants of table 33. 



This, of course, does not vitiate our main result, that inherited 

 differentiation does arise within a pure line, and it leaves it 



