REGENERATION- IN LUMBRICULUS. 305 



vicinity of the wound. This enlargement is no more rapid in one 

 part than in another; it continues longer in the ventral cells so 

 that by the second day it is greater there. 



1 1 . The metamorphosis of the ectoderm is not in all probability 

 due to the proximity of the neoblasts, as supposed by Krecker, 

 but instead to an independent transformation. 



12. The cells of the setigerous glands in the new bud have 

 large nuclei and nucleoli. 



13. A feature common to all the cells which take part in the 

 formation of the tissues in the regenerating bud is the presence of 

 large nuclei and nucleoli. 



14. The amount of nucleolar material present in a cell seems to 

 be an index of the activity of its nucleus both in cell-metabolism 

 and in preparation for cell division. 



15. In Lumbriculns there is no evidence of any division or 

 even of a clearly defined constriction in any of the nuclei of the 

 gut which contain two nucleoli. 



1 6. The presence of two nucleoli in a single nucleus is not a step 

 in amitosis, as many have supposed, but is due to the increase in 

 nucleolar substance beyond the amount which can exist within 

 that particular nucleus as a single droplet. 



17. The various tissues seem to be derived in the same manner 

 both in anterior and in posterior regeneration. 



CONCLUSIONS. 



1. Both in anterior and in posterior regeneration the mesoderm 

 is formed from neoblasts. Iwanow and Krecker are in error in 

 the belief that cells from old specialized mesodermal structures 

 form the new ones in the anterior regeneration of Lumbricidus. 



2. There is a certain predetermined area of the hypodermis on 

 the ventral side which metamorphoses preparatory to the for- 

 mation of new nervous tissue during regeneration. The cells of 

 this region are probably activated by the same stimulus as are 

 the neoblasts. Krecker's view that the neoblasts have an inciting 

 effect on the cells of this region seems unfounded. 



3. The amount of nucleolar material present in a cell seems to 

 be an index of the activity of its nucleus both in cell-metabolism 

 and in preparation for cell division. Two nucleoli within a single 



