344 ^- ^^- Stevens and A. M. Boring. 



accumulation at the regenerating end n, suggesting this accumu- 

 lation as the chief source of the cells in the new part. Some of the 

 cells come from the dorsal side, but the evidence from the exami- 

 nation of many sections is convincing that the majority come from 

 the ventral side. 



The muscle cells must develop from the parenchyma cells m 

 situ, as they appear below the ectodermal parenchyma only in 

 pieces which have been regenerating several days. (Fig. 8, g.) In 

 Fig. 6, a section of a piece before the accumulation of nuclei had 

 begun, some fibers appear scattered irregularly through the 

 parenchyma near the end, but these are probably old fibers, as 

 this section shows no definite layer of muscle fibers below the ecto- 

 dermal parenchyma at the regenerating end. 



The seven-day and ten-day sections show an increase in the 

 length of the new part, but no other new points. In two weeks, 

 most of the new tissue has taken on the loose parenchymatous 

 character of the old part, as shown by the spaces in the tissue and 

 the more scattered position of the nuclei in Fig. io,\^only the 

 extreme end of the regenerated tissue still having the nuclei in 

 close proximity and the cells densely packed together. (The 

 dotted Imes in Figs. 9-12 show approximately the boundary 

 between old and new parts.) 



In the regeneration of one of the oldest head-pieces, a new 

 digestive opening has formed. (Fig. II, x.) It is in all respects 

 like the opening in a full sized worm, being situated about halfway 

 between the anterior and posterior ends, and opening directly 

 from the digestive region to the exterior. Middle-pieces of this 

 age have the old digestive opening, but some distance posterior 

 to this, at the base of the new tissue, there is an accumulation of 

 parenchyma and muscle cells, as in Fig. 12, /, which can be 

 recognized as the anlage of the penis, for the sperm has moved 

 down near to this anlage. Anterior to the penis is a slight indenta- 

 tion r which may indicate the anlage of the female genital pore. 



Sections show that anterior regeneration is always slower than 

 posterior; there is less new tissue at the anterior end than at the 

 posterior, and it keeps its compact character and accumulation 

 of nuclei longer than the posterior, as shown by comparing Fig. 7, 

 an anterior end, with Fig. 8, a posterior end of the same age. 

 In some pieces in which the anterior end folded under to form a 

 pocket, as described in Part I, no regeneration can be seen in the 



