AN AMICRONUCLEATE OXYTRICHA. II 



141 



5. STUDY OF THE ORIGIN OF 'TWINS' 



After the initial occurrence of twins, a series of mass cultures 

 of single animals was carried both in Petri-dish cultures and on 

 depression slides for the purpose of ascertaining if further twin 

 formation would occur. These cultures consisted of stock ani- 



Fig. 8 Comparison of typical pedigrees of early selection series (A) and series 

 after considerable selection (B). A represents pedigree of subculture T4 (fig. 7 

 and table 3). Full black circles represent twins; circles represent single animals 

 derived from twins. D, animal died. L, accidentally lost. In the fifth genera- 

 tion (A) an example occurred where a twin (apparently fused normally) separated 

 completely giving two single animals, each of which is therefore still in the fifth 

 generation. 



mals from culture A in which twin formation had not occurred 

 during the course of the experiment, of stock single animals from 

 the various subcultures of series I, i.e. consisting of typical single 

 animals descended from twin ancestors and of stock animals 

 coming from cannibal ancestors. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 30, NO. 1 



