Regeneration in AmpJiinoma Pacifica, etc. loi 



nerve-cord was present as far as the eighth segment from the amputated 

 level. Beginning at the seventh segment the nerve-cord was very narrow 

 and extended in this attenuated condition through the sixth, fifth, fourth, 

 third, second, and first segments. The regenerated nerve-cord had not 

 only reached the amputated level, but extended slightly beyond, into the 

 proliferated embryonic tissues laid down at the cut end. A similar regen- 

 eration of the nerve-cord occurred in worms 13, 9, 45, etc., in which the 

 nerve-cord regenerated two to seven or more segments, and in which the 

 nerve-cord did not always reach or pass beyond the amputated level. 



In the worms whose nerve-cords had regenerated to the amputated 

 level, supplying this region with nervous and trophic stimuli, the lack of 

 regeneration could not have been due to any lack of innervation. 



In a third very small group the head regenerated without the presence 

 of the nerve-cord at the amputated level. In worm No. 7, for example, 

 the characteristic nerve-cord extended as far as the sixth segment from the 

 amputated level. The regenerated nerve-cord was present in the fifth and 

 part of the fourth segment. Beyond this region, i. e., the fourth, the third, 

 the second, and posterior half of the first segment, there was no trace of a 

 nerve-cord. Close to the amputated level and slightly beyond it into the 

 embryonic tissues, there was an unmistakable ganglionic mass, from which 

 there extended posteriorly a short, narrow nerve-commissure. This supra- 

 oesophageal ganglion had been formed independently of the direct contact 

 or stimulation from the regenerating nerve-cord. 



Worm No. 34 affords a much better idea of the development of the newly 

 formed head. The nerve-cord was intact as far as the sixth segment, from 

 which point the regenerated nerve-cord extended through the fifth, fourth, 

 and third segments. The next two segments were entirely free of traces of 

 the nerve-cord. Beyond the amputated level there was a fairly large 

 regenerated head with a clearly differentiated "brain," from which the 

 nerve-commissures extended ventrally and posteriorly almost to the ampu- 

 tated level. These two worms clearly show that it is possible for a head 

 to regenerate with the nerve-cord 2, 3, or more segments from the amputated 

 level. They show that the development of the brain and commissures may 

 secondarily unite with the regenerating nerve-cord, as was found to be the 

 case in Lumbricus. 



In view of the regeneration of the head in Lumhriais, in the absence of 

 innervation from the nerve-cord, and in view of the corroborative results 

 obtained in Amphinoma, it seems evident that regeneration can take place 

 under these circumstances. It is very probable that the presence of the 

 nerve-cord accelerated regeneration. It may also be that regeneration does 

 not take place ordinarily until the amputated level has been innervated 

 from the cells of the nerve-cord as urged by Nussbaum.^ It is equally clear, 

 however, that a head can be regenerated in at least two annelid worms 

 without the aid or stimulus derived from the nerve-cord. 



Nussbaum, Josef. Beitrag zur Frage uber die Abhan5igkeit der Regeneration vom Nervensystem be 

 Nereis diversicolor. Arch. f. Entw., vol. 25. 1908. 



