Sonic IMieiumienu of Rr^'cnuratiou iii Liinuodrilus and related Forms. 437 



B. Anterior Eiid. 

 The Neoblasts. 

 The behavior of the neoblasts at the anterior end of the body is 

 interesting. As montioncd in another part of this paper it has bccn 

 observed that the neoblasts do not take part in regeneration at tlie 

 anterior end, a condition whicli might be explained in several ways. 

 In Tvhifex and LimnodrUus no neoblasts are present in the uninjured 

 worm anterior to the lOth somite and since these worms do not re- 

 generate at the anterior end posterior to about the 8th somite one 

 could suppose that the absence of neoblasts in the case of anterior 

 regeneration is due to their absence froin this region under normal 

 conditions. Biit in the case of regeneration from the posterior end 

 neoblasts migrate t(^ the regenerating region from other segments and 

 thus tlie question arises, are the neoblasts absent from a regenerating 

 surfacc at the anterior end because they can not migrate in an anterior 

 direction or because a wound which exposes an anterior end of a piece 

 does not stimulate the neoblasts or for both of these reasons? The 

 20tli somite is at a level at which neoblasts appear at a posterior re- 

 generating surface and take part in the formation of new tissue, there- 

 fore their behavior with regard to an anterior cut surface at this level 

 may throw some light on the problems just stated. In the instances 

 already described in which the intestine was removed from the anterior 

 end neoblasts were sometimes present in the region äff ected. There were 

 rarely more than two or three und usually only one or two neoblasts. 

 They were generally in the network of muscle and peritoneal cells 

 and never in contact with or very close to the ectoderm. In one or 

 two instances a neoblast was along the nerve in the somite immedia- 

 tely posterior to the wounded one and it was evidently in process of 

 migration toward the anterior end. Occasionally also, either in the 

 injured somite or in the one adjoining it, neoblasts were found at- 

 tached to the septa in their normal resting position and apparently in- 

 active. 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 havo been due to lack of time. Thus it is seen that even when 

 nt'oljlasts are present in the injured somite they take no part in the 

 formation of new tissue. As noted before the sanie is said to be true 

 of Lumbriculus in which form, with the exception of the extreme 

 posterior levels, anterior regeneration occurs at any level; neoblasts 



