364 DONNELL BROOKS YOUNG 
to account for this appearance. Whether regeneration proper 
ever begins or not, this closing in of the cut surface takes place if 
the cell lives for more than a very few hours. The regeneration 
of the posterior end can be followed very easily because the 
cirri are so definite. At first they appear as swellings on the cut 
surface, but these elongate and finally show the characteristic 
shape. Frequently the normal cirrus apparatus does not develop, 
but lacks some of its parts or the parts are abnormally arranged. 
This is especially true of amicronucleate fragments. The re- 
generation of the anterior end is not as easily studied, for the 
anterior membranelles are not as clearly seen as the larger pos- 
terior cirri. At times it is difficult to be sure that the undulating 
membrane, which so often is protruded in front of the body, is 
not mistaken for new membranelles. However, the first evi- 
dence of regeneration is the appearance of slight pits from which 
the membranelles later develop, and by looking for them it is 
possible to be sure that new membranelles are forming. 
When an animal was cut into two parts the power of coordinat- 
ing the movements of the motile organs was destroyed in both 
pieces. For some this lack of control was very apparent, and 
each of the cirri moved independently, frequently in opposition 
to each other. This resulted in a very irregular and erratic 
movement of the fragment. Usually in the course of an hour 
the fragment became quiet and in a few hours the motor organs 
worked in harmony again. 
In Euplotes, one of the closely related hypotrichs, Yocom 
('18) has found a well-organized 'neuromotor' apparatus, which 
he believes acts as a coordinating center for the complicated 
sensory and motor organelles. If such a system should be found 
to exist in Uronychia, the reactions of the fragments could be 
easily explained. Although some time has been spent in a search 
for such a system, none has been seen as yet. As is discussed 
elsewhere, all that can be seen are fibers originating from the 
basal bodies stretching anteriorally. No center body or moto- 
rium is to be found (text fig. C, a and b). 
The loss of coordination mentioned above could be accounted 
for by the severing of neuromotor fibers when an animal was 
