392 KUTH J. STOCKING 



January 14, 1914, to April 1, 1914, was concerned wholly with 

 that problem. In it an attempt was made to ascertain the 

 efficacy of selection as a means of breaking a single clone into 

 two or more lines differing hereditarily in amount or kind of 

 abnormality. 



In all three of the experiments, in two of which very large 

 numbers of exconjugants and their descendants were studied, 

 a large proportion of the resulting races were abnormal, just as 

 was the case in the exconjugants studied by Jennings ('13). 

 In Experiment 1, with a wild population, the proportion of abnor- 

 mals was 36 per cent of the entire 262 exconjugants. In Experi- 

 ment 2, with the members of a clone, the proportion of abnor- 

 mals was much higher, being 81 per cent of the whole 200. In 

 Experiment 3 the number of exconjugants studied was small; 

 the abnormal races formed 43 per cent of the total 28. In the 

 54 members of the 27 split pairs of Experiment 2, twenty of 

 which were cultivated for 19 days, and thirty-four for 7 days, 

 no abnormals at all appeared. Whenever sets of individuals 

 are isolated without conjugation and cultivated in the same way, 

 no such proportion of abnormals are observed; indeed as a rule 

 no abnormals v/hatever are obtained. We shall return later to 

 the relation of the abnormalities to conjugation (page 412). 



The exconjugants from large cultures of paramecia may be 

 divided, on the basis of their subsequent history, into a number 

 of diverse classes, which are summarized for our three cultures 

 in table 1. 1) A few pairs, in some cultures, never separate, 

 but die while united. 2) A considerable number, in some 

 cases, die within 24 hours after separation. 3) Others live 

 after separation — often for a long tiyne — but never divide. 4) 

 A fourth group divide, but produce individuals that are in some 

 way and to some degree abnormal. 5) Finally, a certain pro- 

 portion propagate normally after conjugation, giving rise to 

 typical progeny. The proportions of these different classes are 

 shown in table 1. 



The single pair that did not separate lived united for five days. 

 The exconjugants that never divide after separation form a large 

 proportion of the abnormal individuals, rising to 28 per cent of 



