AN AMICRONUCLEATE OXYTRICHA. II 143 



This series, in general, was much less vigorous than series I, 

 although the structure of the twins was identical with that in 

 the first series. It will be noted that the subculture of single 

 animals (S2T2N) showed much less vitality than the twin sub- 

 cultures. The chief importance attached to this series lies in 

 the fact that it arose by the fusion of single animals which were 

 descendants of a twin subculture (T15). 



Series III. This series was started from a twin isolated De- 

 cember 16, 1917, from a depression slide which contained the 

 progeny of a single 'normal' animal originally isolated for the 

 purpose of studying the conditions under which cannibalism took 

 place. From this slide three cannibals had previously been 

 isolated, and at the time the twin was found, three attached pairs 

 and sixteen apparently normal animals were present. The pedi- 

 gree of this twin was followed for six generations : 



1st generation. 2 twins (one considerably separated). 



2d generation. 1 twin, 4 single. 



3d generation. 1 twin, 10 single. 



4th generation. 2 twins, 20 single. 



5th generation. 1 twin, 44 single. 



6th generation. The remaining twin had separated to give 

 two single'animals. This is the only instance where a twin series 

 ended with complete separation of all 'twins.' The single ani- 

 mals were carried for some time on stock slides and multiplied 

 normally. 



Series IV. On December 6, 1917, a cannibal animal was iso- 

 lated from Petri-dish culture of animals from culture A and 

 placed in culture medium on a depression slide. Among the de- 

 scendants of this animal, about fifty in number, on December 

 18th, several pairs were observed, fused in a manner similar to 

 that previously described in section 2 (pp. 16, 17). One of these 

 pairs was peculiarly attached in the peristomial region of each 

 animal, with the bodies somewhat twisted around each other. 

 This pair, along with several others, was isolated, and on the 

 following day it was found that the animals which were so pe- 

 culiarly attached had become more firmly fused and now formed 

 a typical twin. 



