No. 15. — Regenerative Phenomena following the Removal of the Diges- 

 tive Tube and the Nerve Cord of Earthworms. 



By H. R. Hunt. 



contributions from the zoological laboratory of the museum 

 of comparative zoology at harvard college. no. 317. 



In recent years much interest has been shown among zoologists 

 in attempts to determine the degree of interdependence among the 

 parts of a developing organism. On the one hand, some developing 

 structures are independent of others (self-differentiating). On the 

 other hand, the development of one part may depend upon a " forma- 

 tive stimulus " (Herbst) from another part. For instance, the rela- 

 tion of differentiated nervous tissue to the processes of regeneration 

 and ontogeny has been the subject of much controversy. Nervous 

 stimuli were formerly believed to be important in the regenera- 

 tive and normal developmental processes of embryos, as well as 

 in the regeneration of adults. It has now been demonstrated, 

 however, that in ontogeny nervous stimuli play no important mor- 

 phogenetic role. 



But numerous investigators (Herbst, Przibram, Morgan, Wolff, 

 Walter, and others) ht^ve maintained that regeneration in adults 

 is modified or inhibited in the absence of specific relation of the 

 regenerating parts to nervous tissue. Others, notably Goldfarb 

 ('09, '14), have insisted that regeneration in adults is totally inde- 

 pendent of nervous stimulation. Using modified methods, Gold- 

 farb repeated Morgan's ('02) experiment of removing the nerve cord 

 from the anterior end of a beheaded earthworm, and found that it 

 was possible for the worm to regenerate a normal head while the cut 

 end of the old nerve cord was still several segments back of the re- 

 generating region. In other words, the regeneration of the earth- 

 worm's head is not contingent upon nervous stimuli. 



As a further line of attack upon this problem of interdependence 

 of organs in regeneration, Goldfarb's results suggested removing 

 from the cut surface of a beheaded earthworm some organ not a 

 part of the central nervous system, such as the digestive tube. Fol- 

 lowing such an operation, the regeneration of a normal head before 

 the digestive tube had grown forward to the level of transection 



