Sonic Pliennmcn;i of Regeneration in Limnodrihis ;incl iclatid Fornis. 411 



wliy it sliould uccur. Su far as obsorvable iio iicccssary eleniciits are 

 lacking since as will be shown below, foreigu cells take no parc in the 

 forniation of iiew entoderm. The possibility of a Stimulus to growth 

 boing roquired from the ectoderm is likewise ruled out since regenc- 

 ration of tho entoderm occuivs where thcrc is no connection between 

 tlif I wo. In every individual observed which had been allowed to live 

 for over a week those in which the intestine was removed at otlier 

 levels thaii the lOth showed some stage of regeneration. As mentioned 

 before it is well known that under normal conditions Tuhifex does not 

 regenerate in a posterior direction from a level anterior to the lOth or 

 tlie lltli somite, and since all cases of failure to regenerate after a 

 time were found at the 9th or lOth somites it seems clear that the in- 

 testine failed to regenerate because it was removed at a level too near 

 the anterior end. 



The method of growth of the intestine in normal regeneration 

 has occupied a somewhat secondary position in the literature. When 

 an individual's body is severed the intestine retracts a short distance 

 from the ectoderm and the end is closed. Thereafter, according to 

 Bock (98) in Chaetogaster and Haase (98) in Tubifex, it grows down 

 and fuses with the ectoderm. Hepke (97) claims that ectodermal 

 cells are applied to the hindermost portion of the intestine and form 

 the new entodorm. Michel (98) holds that it is formed from an in- 

 different mass of ectoderm and entoderm which lies between the end 

 "f Ihe intestine and the posterior end of the body whereas Rievel (96) 

 in Nais, Allolobophora and Lumhricus and von Wagner (06) in TAim- 

 briculus agrec with Bock and Haase. In early stages Iwanow (03) 

 in Lunibriculus finds considerable cell proliferation in the entoderm 

 by means of both mitosis and amitosis and since he does not note the 

 addition of foreign cells he coiicludes that the intesthie regenerates 

 from entoderin. 



Where some of the intestine has been removed it is not in proxi- 

 mity to the ectoderm and therefore its regeneration can be followed 

 without difficulty. Under these circumstances addition s to the in- 

 testine are seen to be formed exclusively of entoderm. The process 

 is initiated by the extension of a narrow, median tonguelike projection 

 from the posterior end that is more the result of the stretching of the 

 old entoderm than of the proliferation of new cells (Fig. 6). New 

 cells soon begin to form but, as a matter of fact, comparatively few 

 instances of cells in process of division have been seen although spe- 

 cial search was madc for them. Mitosis and amitosis both occur. The 



