296 



LEONARD P. SAYLES. 



take place at the level of the twentieth somite where these cuts 

 were made. It does not seem strange, therefore, that at the end 

 of three weeks all neoblasts should be resting even if activation 

 had taken place three weeks previous. In Lumbriculus anterior 

 regeneration does take place at all except very posterior levels. 

 The amount of tissue is, of course, limited to a few segments, 

 usually five or six, rarely seven (von Wagner, *oo). 



Counts made of the number of clearly recognizable neoblasts 

 (intermediate and definitive stages of Krecker, '23) present on 

 the various septa in three- and four-day regenerates are given 

 in Table XIV. These cells all possess nucleoli of approximately 



2 M or over (Fig. 14). 



TABLE XIV. 



NEOBLASTS. 



These figures do not differ greatly from those for posterior 

 regenerates (Table IX.). The small number of neoblasts present 

 on the first septum of the three-day regenerate may be explained 

 in part by the fact that this septum was partially torn away by 

 the cut in this particular case. About four segments seem to 

 produce neoblasts more abundantly than the rest and about nine 

 segments in all are apparently involved. The more active region 

 extends farther, however, in the three-day regenerate; the inclu- 

 sion of the first septum in the cut brings this about. The 

 neoblasts, then, are activated to about the same extent as at 

 the posterior end. The number present in the bud at the end 

 of two days, however, indicates that either not as many migrate 

 anteriorly or else the migration is much slower and the cells are 

 used up as they get to the wound. No mass of large cells is to 

 be found in the ventral part but several cells are usually present 

 and a number can generally be found migrating along the nerve 

 cord (Fig. 15). The apparently slow migration of the neoblasts 

 anteriorly is perhaps the reason why the mesoderm in the newly 

 formed head does not show signs of development until after the 



