REGENERATION IX LUMBRICULUS. 



283 



ORIGIN OF NEW TISSUE IN POSTERIOR REGENERATION. 



Endoderm. 



In posterior regeneration in microdrilous annelids the majority 

 of investigators, especially more recently, are agreed on the 

 method of origin of the endodermal structures. Krecker ('10) 

 in Tubifex and Limnodrilus removes a portion of the intestine 

 after cutting a worm and finds that by a proliferation of cells in 

 the old intestine growth takes place until it comes in contact 

 with the ectoderm. He says (p. 411) that "mitosis and amitosis 

 both occur," using as a criterion for the latter "the frequent 

 occurrence of double and elongating nucleoli." He finds that 

 cell division may take place one or two segments anterior to 

 the wound, but when it "was seen at such a distance it was 

 always found to be mitotic . . . ." His observations are verifi- 

 cations of statements to the same effect made by Iwanow ('03). 

 A study of individuals which have been regenerating for various 

 periods reveals that mitoses may and commonly do occur even 

 eleven or twelve segments from the wound region. The distribu- 

 tion of mitotic figures and double nucleoli in worms regenerating 

 for different periods is given in Tables I. to VI., inclusive. 



TABLE I. 



i DAY OF REGENERATION. 



TABLE II. 



2 DAYS OF REGENERATION. 



TABLE III. 



3 DAYS OF REGENERATION. 



