RE GENERA TION 



about accidentally by the worms themselves pulling apart and leav- 

 ing a small piece of one component attached to the other. Joest 

 found that in several cases these small, attached pieces regenerated. 

 In one case, after two long pieces had pulled apart, a small piece, left 

 by one of the two, regenerated a single new segment with a mouth at 

 its end. In another case, after one of the components had been cut 

 off, leaving two segments attached, a new part of seven segments 

 regenerated. 1 Especially interesting is the case in which two indi- 

 viduals (A. terrestris} had been united to form a long worm. The 

 anterior component extended to within two centimetres of the anus ; 

 the posterior piece had had the first four segments removed. Three 

 days later the anterior piece was cut off three segments in front of 

 the region of union. About a month later a small part of eight seg- 

 ments had regenerated from the cut-end (Fig. 53, A). Fifteen days 

 later another new part of thirty-seven segments developed at the end 

 of the first new part (Fig. 53, B). Joest speaks of the first eight seg- 

 ments as a head, and the second simply as a regenerative product. 

 There can be little doubt, I think, that both parts represent a hetero- 

 morphic tail. The region from which the regeneration took place 

 would make this interpretation highly probable, and Joest's figures 

 also indicate that the structure is a tail. The result is very interest- 

 ing, if my interpretation is correct, as it shows that the major com- 

 ponent did not influence the kind of regeneration, although the 

 surface of regeneration was separated by only three tail-segments 

 from the anterior end of the major component. 



In another experiment a long animal was made by uniting Lum- 

 bricus rubellus (whose posterior third had been cut off) and Allolo- 

 bophora terrestris (whose first six segments had been cut off). Four 

 days later the two components had torn apart, but a small piece of 

 the anterior worm remained attached to the 'anterior end of the pos- 

 terior component. The small piece consisted of the dorsal part of 

 two and a half segments without any ventral part, so that the anterior 

 end of the posterior component was partially exposed. The small 

 piece of lumbricus was much lighter in color, and this difference 

 made it easy to distinguish between the two. In less than a month 

 the small transplanted piece had replaced its -missing ventral part, so 

 that the entire anterior surface of the larger component was covered 

 over. The small piece, in addition to regenerating its ventral part 

 of four segments, had also begun to make new segments. After a 

 month and a half six new segments were present (Fig. 52, ), with 

 a mouth at the anterior end. 2 Even after ten months the color of 



1 It is not certain whether this is a head or a tail. 



2 Joest states that this new part is a head, as shown by the presence of food matter in the 

 digestive tract of the posterior piece. 



