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- 
