Heredity in Protozoa 



623 



finished form, like the spine of a (Fig. 4), but are produced anew 

 on each product of fission. The old setae and ciHa degenerate and 

 disappear as fission sets in. In the daughter individuals the new 

 setae appear in a small group with a totally different arrangement 

 from that seen in the adult parent (Fig. 21, x) and the final arrange- 

 ment is reached by complicated processes of differentiation and 

 distribution. Thus the presence of setae in the posterity could 

 have been brought about in the beginning only by such modifica- 

 tions of the protoplasm of the mother cell as would cause it at fis- 

 sion to produce setcc. Any change in the structure, number, or 



Fig. 21 Dividing Stylonychia, from Biitschli, showing at x the appearance of the new setae in a close 

 group 



arrangement of the setae could result only from such a modification 

 of the mother cell as would alter in a definite way the processes 

 occurring at reproduction. The thing transmitted from the 

 parent cell to the young progeny is, not the setae themselves, but 

 the change in the protoplasm causing the production of setae in a 

 definite way. 



To return to a specific problem — How then could such a local- 

 ized appendage as the spine oi a (Fig. 4) become an inherited char- 

 acteristic t Only through such a modification, of the protoplasm 



