CHAPTER VIII 



THE PHYSIOLOGY OF 

 REGENERATION 



One of the most interesting properties of the annehds as a 

 phylum is that of regeneration. Considerable portions of the body 

 can be replaced after loss by injury. The literature on the morpho- 

 genetic aspects of this phenomenon is very great and has been 

 summarized by Stephenson (1930). 



Despite the volume of work published on the morphological 

 changes in regeneration, however, the amount of work available on 

 physiological aspects of this problem is comparatively small. As 

 late as 1948 Scheer wrote a chapter on annelid physiology without 

 mentioning regeneration, and neither Carter (1940) nor Prosser 

 et al. (1950) have much to say on this aspect of the subject. 



Oligochaetes are able to regenerate both the anterior and 

 posterior ends with almost equal facility, the part which is recon- 

 stituted depending upon where the cut is made. A cicatrice forms to 

 seal the wound and then the remoulding of the stump proceeds, 

 followed by the formation and growth of new segments (Stephen- 

 son, 1930) (Fig. 36). The actual process differs from species to 

 species and the ability to provide new segments to replace missing 

 ones is lost in some species but all individuals retain a certain degree 

 of plasticity in the tissue. 



Early morphological studies revealed that the presence of the 

 nervous system is required for regeneration to proceed. Thus if the 

 anterior end was removed, and the ventral nerve cord excised from 

 the first few segments behind the injury, it was found that these 

 latter segments are re-absorbed and regeneration takes place only 

 from the first segments containing a portion of the ventral nerve 

 cord (Carter, 1940). This finding may now be expHcable in terms 

 of the phenomenon of neurosecretion, and will be dealt with later. 



The number of segments that can be re-formed after loss is 



118 



