98 



Papers from the Marine Biological Laboratory at Tortugas. 



deflecting the muscle layers sufficiently to permit the removal of the ex- 

 posed nerve-cord. The muscle walls were then replaced and ligatured. 



There were 90 operations of the first type, 12 of the second, and 151 

 worms served as controls. 



The worms were amputated at different levels and the nerve-cord 

 removed from the anterior as well as the posterior parts. It is well known 

 that the regeneration from the two exposed surfaces at certain levels may 

 be quite different. The flatworm Dendroccelum lacteum,^ for example, regen- 

 erated a tail from the anterior piece and a head from the posterior piece, 

 provided the amputation was not made more than one-third from the 

 anterior end. Posterior to this level the head piece regenerated a tail, but 

 the tail piece did not regenerate a head. In the earthworm Lumbricus the 

 same phenomenon occurs. The differentiating level occurs at about the 

 fifteenth segment. 



Amphinoma differs from this type of regeneration in two respects: 

 (i) the level at which the two cut surfaces can regenerate is much more 

 posterior, i. e., about the middle of the body; (2) instead of the regenerative 

 power of the tail pieces being limited to certain narrowly prescribed levels, 

 the reverse obtains, i. e., head pieces can regenerate tails only in the 

 posterior half or third of the worm, while tail pieces regenerate heads at 

 practically all levels. 



Table i gives some details of the regeneration in the head pieces of con- 

 trol worms, i. e., level amputated, the number that regenerated a tail, etc. 

 It is evident that no head piece regenerated when amputated less than 

 one-eighth from the anterior end of the worm. Between the third and the 

 middle of the body some of the pieces regenerated, others did not. All, 

 however, regenerated posterior to the forty-fifth segment or middle of the 

 body. 



In table 2 similar data are given for tail pieces of control worms. The 

 data are arranged with respect to the level amputated and the number that 

 did or did not regenerate. All of the tail pieces regenerated a head from 

 the first quarter, the middle, and even from the distal quarter of the worm. 

 Beyond this level a number of pieces did not regenerate. There were 9 

 such pieces that formed no head. Of these, 5 were small distal pieces 

 12 to 17 segments from the distal end, and probably too small to regenerate; 

 in the other 4, I have no records of the exact level amputated. 



