438 l^'- H. Krcckcr. 



are at times present in tlie soniite in whicli anterior regeneration is 

 occurring but still they take no part in the formation of new tissue. 

 Tlius the mere fact of the presence or absence of neoblasts in the so- 

 mites concerned when the individual is iininjured has evidently no 

 infliience on whether or not they take part in the anterior regeneration. 

 However, the fact that neoblasts may be wandering about in the in- 

 jured soniite or migrating along the nerve indicates that when an 

 individual's body is severed so as to expose an anterior cut surface 

 neoblasts may leave their places of rest and are able to migrate toward 

 the anterior end of the body. Nevertheless, the fact that so few 

 neoblasts were observed in this more or less active state and even 

 these in only about fifty per cent of the cases, demonstrates that 

 the Stimulus to activity, when an anterior cut surface is exposed , is 

 neither so great nor so constant as when the surface is at the poste- 

 rior end of a piece. 



Other Structures including the Mesoderm. 



There is not much to be said, aside from what has been told con- 

 cerning the neoblasts, with regard to the internal condition of those 

 individuals from which a bit of the intestine was removed at the 20th 

 somite since in Tuhifex and Limnodrilus regeneration did not take 

 place from the anterior end at the level of the 20th somite. The cut 

 end of the intestine healed but did not regenerate. The mesoderm, 

 especially the musculature of the body wall, was in much the same 

 condition as that at the posterior end of pieces from which the intestine 

 had been removed. The muscle fibers became loose and wandered out 

 into the coelom where together with the connective tissue and the 

 peritoneal cells they formed a dense mass of irregularly interlaced 

 cells. 



Because Morgan's description of the internal conditions in the 

 anterior intestineless tongues of Lumbricus is so sliort and his figure 

 not as detailed as it miglit be it may not be amiss to give the matter 

 some attention here. Microscopically it is seen still more clearly than 

 macroscopically that tlierc is a great difference between the abnormal 

 growth and that normally regenerated. The normal growth arises 

 from the entire cut surface, its walls being a direct continuation of 

 the old body walls and tapering gradually toward the anterior end, 

 in addition to which the circular and the longitudinal muscles are 

 w(!ll developed. In the abnormal growth the tongue of new tissue is 

 liardly more than a sliell of epidermis lined with a thin \ayei of muscle 



