MORPHOLOGY AND PHYSIOLOGY OF GENUS URONYCHIA 383 



division of the cut, and the amount of mechanical injury done 

 by the cut. For instance, the smaller fragment in experiment 

 no. 61 was killed by crushing. In experiment no. 13 the cut 

 was made three hours and ten minutes after division and the 

 smaller parts constituted nearly one-fourth of the whole cell, 

 yet regeneration was only partial. While in the case of the 

 smaller part of no. 159, which constituted nearly half of the 

 cell, regeneration was complete, even though the cut was made 

 an hour after division. 



Twenty-six individuals were cut through the middle of the 

 cell in such a way that one micronucleus was present in each 

 fragment. In all of these cases, regeneration was complete and 

 division followed. It is not known what nuclear changes are 

 involved in regeneration and subsequent division. 



DISCUSSION AND CONCLUSIONS 



The study of the three species of Uronychia found at Woods 

 Hole, both of normal individuals and of those which were used 

 for experimental purposes, seems to point to rather definite con- 

 clusions as to the function of certain cell organs. Because of 

 the difference in nuclear structure in these species it is possible 

 to use one as a control for the others. 



Various functions have been ascribed to the micronucleus of 

 the ciliates, including its activity in connection with regenera- 

 tion. Gruber ('85) thought that in Stentor, at least, the mi- 

 cronucleus was not as important for regeneration as the macronu- 

 cleus. He based this conclusion on the fact that in fragments 

 of conjugating Stentor no regeneration takes place until one of 

 the micronuclei takes on the form of the macronucleus. Stevens 

 ('04) , on the other hand, found that in Lichnophora no regenera- 

 tion takes place unless both the macronucleus and micronucleus 

 are present, and even then only slightly. Lewin ('10) agreed 

 with Gruber and did not believe that the micronucleus is needed 

 for regeneration or even for growth and division in Paramecium 

 caudatum. He based his conclusions on the fact that he found 

 a monster with the nuclear elements unequally distributed which, 

 he claimed, produced on division a race of amicronucleate indi- 



