Some Phenomena of Regeneration in Limnodrilus and related Forma. 391 



was a setigerous somite. By Dec. 15th two of the 5 — 9 pieces had oiie 

 Segment of new tissue posteriorly in which 6 somites were indicated 

 and at the anterior end they had one-half segment of new tissue. Two 

 others had some posterior regeneration but none at the anterior end. 

 Four of the 6 — 10 pieces had one to one and a half segments oi new 

 tissue posteriorly in which 6 somites were indicated. At the anterior 

 end they had one-half segment of new tissue. 



•Ith Series — Oct. 24th 08. Twenty worms were used. The pieces 

 were 6 somites long; thus 1—6, 2—7, 3—8, 4—9, 5—10, 6—11, 7—12, 

 8 — 13. 1 — 6 died in a few days. At the end of the first week seven 

 of the pieces 4 — 9 had a head and posteriorly from three to four Seg- 

 ments of new tissue in which 9 to 10 somites were indicated. In two 

 weeks twelve of the pieces from the level 2 — 7 had a slight indication of 

 regeneration posteriorly but it did not increase. Three of the pieces 

 6 — 11 had a head and one-half to one and one-half segments of new 

 tissue at the posterior end, in which several somites were indicated. 

 All of the level 5 — 10 regenerated one-half segment at the anterior end 

 and had formed an oral opening while at the posterior end they had 

 regenerated from one to three segments with 10 new somites. In three 

 weeks six of the pieces 7 — 12 had a head and at the posterior end two 

 segments of new tissue with several new somites. Two of the level 

 8 — 13 had a head and posteriorly one segment of new tissue. 



5th Series — Dec. 20th 08. Twenty pieces were cut at each of 

 the following levels: 1—7, 2—8, 3—9, 1—8, 1—9. One piece from 

 the level 1 — 7 and two from the level 1 — 8 regenerated the anal seg- 

 ment. Four pieces from the level 2 — 8 formed a head and at the 

 posterior end a short piece of new tissue and six pieces from the level 

 3 — 9 did the same. 



From the above records we see that the area from which headless 

 pieces capable of forming a complete worm can be taken is rather 

 limited and that even in this region the minimal size varies for different 

 levels. Unless they consist of at least seven somites head pieces will 

 not regenerate at the posterior end. However this is not entirely 

 comparable to pieces from other regions since in this case a head is 

 present. At the level of the second somite seven somites were also 

 required but here the posterior liniit is the eighth somite. For the 

 3rd level there is a decrease of two somites in the number required, 

 it being five i. e. 3—7, although the six somites 3—8 regenerate more 

 frequently. At the fourth level the minimal size is four somites i. e. 

 4 — 7, however here also regeneration is not frequent. The minimal 



