REGENERATION AND REGULATION IN PARAME- 



CIUM CAUDATUM. 



FLORENCE PEEBLES, PH.D. 



The investigations described here were begun in February, 

 1910, upon some pure lines supplied through the courtesy of 

 Professor Jennings. The experiments were undertaken with the 

 hope of determining how new races arise, and if possible, to 

 produce by artificial means, a new race differing in size and 

 perhaps in other characteristics from the parent stock. 



A long series of experiments was carried on, testing the effect 

 of various foods, and also subjecting the organisms to other 

 changes in the environment. The conjugation of a large and a 

 small individual was followed in order to see if the size of the 

 ex-conjugants was modified by the inequality of the gametes. 

 It was found impossible by any of these methods to produce a 

 race with new characteristics. 



In the winter of 1910-1911 a study of the regenerative and 

 regulative power of single individuals and of conjugating pairs 

 was undertaken. It was hoped that after the removal of part 

 of the cytoplasm, and possibly some of the nuclear material as 

 well, a small race might be produced. It soon became evident 

 that the removal of the nuclear material was not possible, for 

 no cell or fragment of a cell (unless cut while in the process of 

 division) recovered after the nucleus was injured. Owing to 

 the extremely small number of successful operations, and the 

 alluring interest of various side issues which arose in connection 

 with the work the main problem was neglected for a time and 

 other experiments, which will be described in this paper, have 

 been carried on at intervals up to the present date. 



In November, 1910, in a paper read before the Cambridge 

 Philosophical Society, Levin ('10) described very briefly some 

 experiments on Paramecium in which he produced races without 

 a micronucleus, and others where he found it possible to divide 

 a living cell so that each fragment received a portion of the 



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