578 SUMMARY OF CURRENT RESEARCHES RELATING TO 



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 6 somites. 



In Lumbriadus pieces of the same size from the same level of different 

 individuals do not regenerate the same number of somites at the poste- 

 rior end in the same length of time (two weeks), nor in a succeeding 

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



In Lumbriculus the minimal size of a piece from the posterior end 

 of the body capable of regenerating is 35 somites, while ten somites from 

 the posterior end it is 25 somites. In IAmnodrilus the last four, con- 

 secutive pieces 12-15 somites long, do not regenerate. 



In Limnodrilus 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 intestine does not 

 touch the posterior end of the body-wall, no regeneration takes place 

 from this point. The posterior end of the intestine which ends free in 

 the ccelom regenerates until it comes in contact with the posterior end 

 of the body -wall, after which regeneration of the entire body begins at 

 this point. In Tubifex, when a portion of the intestine is removed from 

 the anterior end of an individual at a level posterior to the point at 

 which anterior regeneration of the body-wall takes place, the anterior 

 end of the intestine will not regenerate. In Lwnbricus hercideus, 

 when a portion of the intestine is removed from the anterior end within 

 the region in which a head is formed, so that the intestine does not 

 touch the body-wall, the body-wall will regenerate a tongue of new tissue 

 in which no alimentary tract is present. The presence of an alimentary 

 tract is therefore probably not necessary for the regeneration of the 

 body-wall at the anterior end of Lwnbricus hercuhus. 



When the intestine has been removed from the posterior end of 

 Limnodrilus and Tubifex the wound closes in the same manner as it 

 does under normal circumstances, but thereupon the muscle fibrils of 

 the body-wall musculature stream out into the ccelom and, together with 

 peritoneal cells, chloragogen and connective-tissue, form a strand which 

 extends from the posterior end of the body-wall to the posterior end of 

 the intestine. Somewhat similar strands appear to be formed at other 

 points wherever the continuity of the body-wall musculature has been 

 broken. The intestine of Limnodrilus and Tubifex is regenerated from 

 endoderm alone. When the intestine regenerates independently of the 

 body-wall the intestinal musculature is regenerated from the old intes- 

 tinal musculature. Under the same conditions the chloragogen is re- 

 generated from the old chloragogen. A proctodaeum was found to form 

 according to the method described by Abel. An abnormal anal opening 

 found in Tubifex was probably caused by the entoderm coming in contact 

 with the body-wall. The ectoderm enters the ccelom to form mesoderm 

 {Tubifex and Limnodrilus). The neoblasts perform no phagocytic func- 

 tion. At the posterior end of the body the secondary mesoderm, i.e. the 

 longitudinal muscles of the body-wall, the septa, etc., is regenerated 

 from the neoblasts (Tubifex and Limnodrilus). The circular muscles of 

 the bodv-wall are regenerated from the ectoderm cells in situ. When 

 the regeneration of the body-wall does not occur in the absence of the 



