hunt: regenerative phenomena in earthworms. 573 



Number 66. Hclodrilus caliginosus (Savigny). The three most 

 anterior segments had been removed and the digestive tube cut out 

 from five segments more. The worm was killed sixty-one days after 

 the operation. At this time a knob of regenerated tissue was ob- 

 served externally at the anterior end of the body. A study of the 

 sections showed that the knob possessed the characteristics of re- 

 generated tissue (Fig. 1). The digestive tube (trt. in.) had grown 

 forward so that its anterior end was imbedded in the mass of cells 

 inside the knob. A thickening of the epithelium lining the dorsal 

 side of the tube at its anterior end suggests that the process of form- 

 ing a pharynx had begun.- Brain (cb.) and connectives were regen- 

 erating. A horizontally elongated stomodeum (stmd.) had developed. 

 Seven other worms showed practically the same phenomena as 

 number 66. 



In fourteen worms the digestive tube had regenerated so far for- 

 ward that the lumen had come into communication with the outside, 

 while the fundaments of the brain and connectives also had reformed. 

 These twenty-two cases prove conclusively that after an operation 

 of this kind the alimentary canal can grow forward to the anterior 

 end, and the process of regenerating a head can proceed, in its main 

 aspects at least, in a normal way. 



However, six other operated worms, described below, furnished 

 much more interesting and instructive phenomena, in that they 

 showed the regeneration of head structures before the digestive tube 

 had grown forward. 



Number 67. Helodrilu^ caliginosus. The three most anterior 

 segments of the body were cut off and the digestive tube excised from 

 the next four segments. Thirty-eight days later a cone of regenerated 

 tissue was observed at the anterior end; consequently the worm was 

 then killed. The cut end of the digestive tube had closed and was 

 covered by epithelium. This end was distant from the anterior end 

 of the worm a little more than the length of three segments. A 

 columnar epidermis, possessing a cuticula, covered the surface of the 

 cone-shaped mass of regenerated tissue (Fig. 2). Regenerated circu- 

 lar (mw. crc.) and longitudinal muscle fibers {inu. Ig.), of smaller 

 diameter than those in the old part of the body, occurred in their 

 normal positions in the cone. 



A brain {cb.) was found dorsal to the anterior end of the nerve cord 

 in the regenerated tissue. A pair of connectives joined this brain 

 with the ventral nerve cord {71.V.). The brain was certainly a re- 



