hunt: regenerative phenomena in earthworms. 577 



digestive tube had grown forward to the anterior end. But the 

 failure of the head to regenerate under these conditions may have 

 been due to the two folio-wing causes. In the first place, the wounds 

 healed normally and completely in only twenty of the worms. Sec- 

 ondly, but nine of these twenty showed positive evidence of any 

 regenerative activity. The low temperature at which the worms 

 were kept seems to have retarded regeneration. (The nerve cord 

 was used as an index of such activity, because one can recognize 

 regenerated tissue more easily in the cord than in the digestive tube). 

 Thus an unfortunate combination of unsatisfactory wound healing 

 and a very slow rate of regeneration, rather than the absence of ali- 

 mentary canal and nerve cord at the head end, may have been responsi- 

 ble for the failure of head structures to regenerate as expected. How- 

 ever, the experiments furnished significant results. 



In one animal the nerve cord and digestive tube had grown forward 

 to the anterior end in thirty-nine days after the operation. The 

 tube was open to the outside and its dorsal wall in the anterior region 

 was lined by a thickened ciliated epithelium, indicating that the 

 pharynx had reformed. A new brain was situated dorsal to the 

 anterior end of the digestive tube, and the connectives, encircling the 

 tube in the normal way, united the brain with the forward end of the 

 regenerated nerve cord. This case clearly shows that the forward 

 regeneration of the cord and alimentary canal is not conditional upon 

 the close proximity of regenerating cephalic structures. 



Another interesting phenomenon was found in five worms from 

 this group of experiments. A detailed description of one of the five 

 cases, number 433, will suffice. 



Three anterior segments were removed from this worm, then the 

 digestive tube and the nerve cord were cut out from the five succeed- 

 ing segments. There was no external evidence of regeneration at the 

 end of fifty-eight days. The anterior extremities of both alimentary 

 canal and ventral nerve chain were a little more than four segments 

 from the front end of the body. A strip of scar tissue extended 

 antero-posteriorly along the dorsal side of the worm, where the longi- 

 tudinal cut had healed. Just dorsal to the end of the digestive tube 

 a long, slender invagination extended from the scar tissue ventrally 

 across the front of the tube (Fig. 5, ivg.d.). The invagination did 

 not open into the aUmentary canal {trt.in.), though long enough to do 

 so. A plainly visible cuticula over most of the surface of the lumen 

 and the arrangement o^ nuclei around the invagination showed that 

 it doubtless had an epithelial lining. 



