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- 



