REGENERATION IN A TROPICAL EARTHWORM. 353 



lies easy. The dark red color of the normal segments sharply 

 sets off the much lighter colored new tissue during the early weeks 

 of regeneration and the presence of a protruding fleshy prosto- 

 mium distinguishes a regenerating head from any other structure. 



Only fully mature and normal worms were used. They were 

 anaesthetized in a weak solution of chloretone and an excision was 

 made by a clean cut, usually at an intersegmental furrow. The 

 operated worms were kept in closed jars containing moist paper 

 towelling. All results described in this paper were obtained in 

 that part of the year known locally as the " cold season." The 

 term is of course merely relative and indicates that the mercury is 

 slightly lower all day long than at other seasons of the year. No 

 effort was made to control the temperature but in the brick lab- 

 oratory building the fluctuations of the mercury from midday to 

 midnight are much less marked at this season of the year than out 

 of doors. 



In a short time after the operation a transparent conical out- 

 growth was visible at the cut end. In the case of regenerating 

 anterior ends, oval faecal pellets were found from the sixth day 

 on, indicating that the digestive system had developed sufficiently 

 in that short time to enable the worm to " bite " off, swallow, pass 

 through the digestive system, and defecate pieces of the paper 

 towelling. By the end of the second week the segmental differ- 

 entiation of the regenerating heads was completed. Usually by 

 the end of the third week the new segments contiguous to the old 

 tail piece had attained the diameter of the metameres with which 

 they were in contact, and were clearly setigerous. In the fourth 

 week the pigment appeared in the regenerating segments. 



REGENERATION OF ANTERIOR ENDS. 



In all series of operations every surviving worm from which 

 six or fewer segments had been amputated regenerated the exact 

 number lost. If the prostomium or a fraction of the prostomium 

 was removed a new prostomium or the missing fraction was re- 

 placed. In several worms a small wedge-shaped piece was re- 

 moved dorsally, laterally, or ventrally from the anterior end of 

 the stump. In each case such wedge-shaped pieces were replaced 

 as well as the exact number of missing anterior segments. Only 



