444 F. H. Kieckcr, 



Summary. 



J) This paper deals witli phenomena of regeiieration in Limno- 

 drilus, Tubifex, Lumbricidus aiicl Lumbricus. 



2) Limnodnlus does not regenerate a head wlien more than seveu 

 somites have been removed. An interesting point brought out is tlie 

 small amount of new tissue regenerated at the anterior end. No indi- 

 vidual replaced more than one and a half segments which was the 

 case when the first three somites were removed and the entire amount 

 removed was regenerated only when the first somite alone had been 

 cut off. 



3) Altiiüugh lack of movements proper to the head end may prevent 

 the worin {Limnodrilus) from burrowing when the anterior segments 

 have been removed posterior to the level at which a head regenerates 

 still it seems probable that it is also in part due to the important fact 

 that the bluntness of the anterior end in this region prevents the worm 

 from cleaving its way into the mud. 



4) For Linmodrilus the minimal size of a piece, at different levels 

 within the head forming region capable of regeneration, is as follows, 

 A head piece will not regenerate unless it consists of at least 7 somites. 

 At the level of the second somite the minimal piece is also 7 somites, 

 2 — 8. At the level of the third somite it is 5 somites, 3 — 7. At the 

 level of the fourth somite it is 4 — 7. At the level of the fifth somite 

 it is 3 somites, 5 — 7. This is the shortest piece of this worm capable 

 of regenerating at both the anterior and the posterior ends. At the 

 level of the sixth somite the minimal size is 4 somites. At the level 

 of the seventh somite it is also 4 somites and at the level of the eighth 

 somite it is G somites. 



5) In Lunibriculus pieces of the same size from the same level of 

 different individuals do not regenerate the same number of somites 

 at the posterior end in the same length of time (two weeks) nor in a 

 succeeding period of equal length. The same result holds true for 

 Limnodnlus. 



G) In Lumbriculus the minimal size of a piece from the posterior 

 end of the body capable of regenerating is 35 somites while ten so- 

 mites from the posterior end it is 25 somites. In Limnodnlus the 

 last four, consecutive pieces 12 — 15 somites long, do not regenerate. 



7) In Limnodnlus and Tubifex the presence of the intestine is 

 necessary at the posterior end of the body for regeneration to occur 

 from this point. When a bit of the intestine is removed so that the 



