30G H. S. JENNINCxS 



Diagram of history of these experiments. We have already 

 (page 302) given some account of the race k. To make clear the 

 conditions in the present series of experiments, I give a diagram 

 (fig. 1) showing the histor}^ of the various divisions of this race 

 with which we are dealing; reference to this diagram should 

 frequently be made in reading the text. The race k as dealt with 

 in these experiments was derived from a single ex-conjugant of 

 November 9, 1908; before these experiments were undertaken, 

 it had passed through three self-fertilizations, or conjugations 

 with inbreeding; that is, all the sur\d\dng members of the race 

 were descendants by fission of a single individual of the preceding 

 conjugation; so that the two individuals that make up a pair were 

 thus descended from one. (In a fourth conjugation in the 

 series, on March 9, 1909, 25 pairs were saved, so that all came 

 from these; see diagram, fig. 1.) 



After the fourth conjugation, of May 24, 1909, the culture was 

 allowed to rest till January 29, 1910; during the interval there 

 may have been many conjugations, in which of course the indi- 

 viduals would mate at random. On January 29, 1910, a pair 

 was isolated, from a single member of which came the line of cul- 

 tures which we shall call B; it forms the branch designated B 

 in our diagram (fig. 1). 



In the remainder of this culture a new conjugation occurred 

 March 4, 1910. At this time there were isolated certain ex-con- 

 jugants, one of which gives the series forming the branch C, one 

 of the three main branches in our diagram; there were also 



Fig. 1. Diagram showing the nature and history of Experiments 5 to 14, and 

 the history of the pure strain k, employed in this work. The rectangles (bounded 

 by broken lines) indicate each an experiment, and show what sorts of individuals 

 were compared, with the history of each. A united pair indicates the progeny of 

 conjugants; a single individual, the progeny of non-conjugants. Thus, in Experi- 

 ment 9, there were compared the progeny of non-conjugants (of branch .4 ), and of 

 conjugants (branch B) that had gone through four conjugations since the others 

 had conjugated. The dates beside each rectangle show the length of time that 

 this experiment lasted. The numbers in or (near) the rectangles give the number 

 under which the experiment is described in the text. The pairs at the left show 

 (with dates) the known self-fertilizations that the race had undergone before these 

 experiments began, the survivors being in each case derived from a single ex-con- 

 jugant, save after the conjugation of March 9, 1909. 



