159 



The Direction of Differentiation in a Regenerating 

 Appendage. 



By Charles Zeleny. 



(Abstract.) 



When an appendage possessing the power of regeneration is removed 

 a proliferation of new cells takes place at the cut surface. At first the 

 structures of the new appendage can not be recognized in this cell mass, 

 but gradually the various parts appear. The problem presented for solu- 

 tion is the determination of the manner of this differentiation. Do all 

 the parts of the new appendage appear simultaneously? If not, is the 

 progression of the differentiation from the tip inward, from the base 

 outward, or from the middle toward both ends? Or finally, is the method 

 more complex than any one of these? 



The antennule of the common brook sow-bug (Asellus) was chosen as 

 a suitable object for the study of the problem because the structural 

 differences in its various segments are unusually great. A study of the 

 early stages of the regeneration shows that the first segmental partitions 

 appear at the base. These are followed very soon by others at the tip, 

 and from this time on the new segments appear near the middle of the 

 organ. The region of new growth is then located in one of the middle 

 segments. Differentiation therefore proceeds from both base and tip 

 toward the middle of the appendage. 



An examination of the growing antennule of young animals shows 

 the same method of development. 



