REGEXERATION IX LUMBRICULUS. 2Q5 



to this the presence of many other cells of similar appearance 

 make it practically impossible to say, from an examination of 

 fixed specimens, just what cells do form the various tissues. 

 Since in posterior regeneration it is quite apparent that ectoderm 

 is not involved in the formation of the septa or longitudinal 

 muscles it seems reasonable to assume that it does not take part 

 here. This view is supported further by the fact that cells of 

 mesodermal origin are present in the bud. 



Regarding the conception that there is a partial dedifferenti- 

 ation of the old muscle cells which then form the longitudinal 

 musculature of the bud, there seems to be conflicting evidence. 

 These cells certainly do fray out and some of them seem to lose 

 their contractile substance in the segment injured by the cnt. 

 Such a behavior is not, however, peculiar to the anterior end in 

 Lumbriculus inconstans. Just as other cells are affected by the 

 cut so many muscle cells are dislodged or injured. It is not 

 improbable that such* cells should then lose their contractile 

 substance due to the injury; such a change might, therefore, 

 be a step on the road to destruction rather than on that to 

 repair. The fact that this same sort of change does take place 

 at a posterior cut-surface, where the muscle cells are not involved 

 in the regenerative processes, seems to support this view. The 

 migrating spindle-shaped cells, which appear between the first 

 and second days in Lumbriculus, are clearly derived from the 

 hypodermis (Fig. 13). These cells migrate into the ccelom and 

 there form the cerebral ganglion. It may perhaps be this type 

 of cell which has been observed by Krecker in Tubifex and 

 Limnodrilus. 



Further evidence is derived from a study of neoblasts in 

 anterior regenerates. Krecker finds that in the species with 

 which he worked they are usually not activated at all posterior 

 to a cut and that resting neoblasts may be found on a nearby 

 septum. 'The individuals upon which these observations were 

 made were all killed three weeks or more after the operation so 

 that the failure of the neoblasts to act as they do at the posterior 

 end could hardly have been due to lack of time" (Krecker, '10, 

 p. 437). In the individuals used in his experiments of the 

 genera Tubifex and Limnodrilus anterior regeneration does not 



