456 Gary N. Calkins. 



there is a complete change of materials or of protoplasmic make- 

 up, and a thorough "reorganization," to use the excellent term 

 proposed by Engelmann. Not only is there a new conjoint micro- 

 nucleus with its chemical compounds derived from the union of 

 two nuclei from individuals of diverse environment, but the endo- 

 plasm and cortical plasm must receive new materials through the 

 disintegration and the absorption of the old macronucleus, and of 

 at least three-quarters of the old micronucleus. If, as I have long 

 maintained, there is a specific "kinetic" substance in the proto- 

 zoon nucleus, a substance which in the centro-nuclei forms the 

 division-center and which is found in the micronucleus of Para- 

 moecium, then the cytoplasm of Paramcecium must receive a 

 certain amount of "kinoplasm" at each period of conjugation 

 and from the experiments, enough to carry the race through a 

 complete cycle. In my cultures such reorganization by conjuga- 

 tion was prevented in the straight line of the experiments, and the 

 only opportunity for reorganization came with the change in diet. 

 This, indeed, seemed to be operative for some time, but ultimately 

 failed, as we have seen. In the stock material, however, material 

 left over after the individuals had been selected for the cultures, 

 conjugation experiments were frequently tried during the course 

 of the experiments, and the results have been given (Studies I). 

 Some of the results are very suggestive in the present connection, 

 for it was found that only a few of the ex-conjugants continued to 

 live, approximately 6 per cent of them. This result may be due, as 

 I have previously stated, to the fact that both of the gametes had 

 been under identical conditions of food, etc., and no new sub- 

 stances were formed by the union of similar nuclei and protoplasm. 

 Or the result may be due to the fact which Stevens^ calls attention 

 to, that conjugation is an exhausting process, and that, being 

 weakened through long cultivation in cultures, these ex-conjugants 

 did not have sufficient vitality to recover. This suggestion does 

 not set aside all of the difficulties, however, for we have still to ex- 

 plain the large number of cases where the ex-conjugants have lived 



^N. M. Stevens Further Studies on the Ciliate Infusoria, Lichnophora and 

 Boveria. Arch. f. Protistenk., Ill, 1903. 



