292 HEREDITY IN THE PROTOZOA 
two pieces, the cut passing between the two nuclei, 
each half will remain alive and later continue to 
reproduce by fission. The first offspring produced 
are smaller than normal, and contain but a single 
nucleus (B' in Fig. 68). The offspring that they 
produce are in turn larger (B? in Fig. 68). They 
may still possess only one nucleus. But soon a 
division takes place of such a sort that an empty 
shell is formed (A-B in Fig. 69), while the mother 
individual that produced the empty shell is now 
found to contain two nuclei and has increased in 
size (C in Fig. 69). Its next offspring is still larger, 
and in the next or in a later generation the full size 
of the Arcella is regained. 
There is present in Arcella a net of chromidia 
(A in Fig. 68), that forms a ring around the space 
between the two nuclei. A portion of the proto- 
plasm was cut off by Hegner in such a way that some 
of the chromidial ring was removed although both 
nuclei remained. When the operated individual 
gave rise by fission to a daughter, the latter was 
smaller than normal. Hegner attributes its size 
to the smaller amount of cytoplasm in the mother 
at this time, and not directly to the loss of chromidia. 
When the daughter in turn produces a daughter, it 
is found to be normal or to more nearly approach 
the normal size. It is apparent, then, that if the 
initial decrease is ascribed to the loss of chromidial 
material rather than to protoplasm in general, it 
must be admitted that Arcella can sooner or later 
make good the loss sustained. It may seem doubt- 
