Regeneration m Lunibriculus c67 



ing the time intervening between October 31 and November 14, 

 all these microscopical segments increase in size very much, their 

 setae became large, and the blood vascular system quite conspicu- 

 ous, as in older segments; but no more ' anlage" of segments have 

 made their appearance. The last large segment was contiguous 

 to the anal segment. 



This result shows that when a new regenerated tail regenerates 

 a head, and thus forms a little worm, although the segments 

 grow larger, no new segments are laid down at the posterior end. 

 Whether the same holds true also for non-regenerated posterior 

 ends of Lunibriculus, I do not know, since in all cases when pos- 

 terior ends were removed they died. 



/; November 14. Again twenty-eight regenerated Ai tails, and 

 thirty Bi tails were obtained from the same pieces as the fore- 

 going at the third and fifth levels, which had been regenerating 

 from October 31 till November 14, or for two weeks. 



November 28, I found alive out of fifty-eight tails (Ai, Bj 

 eleven A^ and seven Bp They all had regenerated new heads, 

 although the number of segments in these heads was in some cases 

 only four. Thus about one-third of all the regenerated tails 

 produced new heads, and eighteen very small worms of about 

 twenty-five to thirty segments each were obtained. In this case 

 also no new segments were laid down at the posterior end, but the 

 segments became larger. 



c November 14, I cut in two all the thirty little worms formed 

 by the regeneration of A and B tails, in order to determine the 

 rate of their posterior regeneration. The cut was made not quite 

 in the middle, so that the posterior parts were somewhat longer 

 than the anterior. 



After a lapse of two weeks, November 28, twelve anterior pieces 

 which came from A, and eight anterior pieces from B, were found 

 alive and regenerating new tails. None of the posterior pieces, 

 although bigger than the anterior ones, had survived. (In other 

 experiments a small percentage of the posterior pieces regenerated 

 heads.) On the whole a very fair percentage (about 65 per cent) 

 of the anterior parts survived the operation and continued to 

 regenerate the missmg tails. 



