100 Papers from the Marine Biological Laboratory at Toringas. 



That regeneration was not prevented by injury to, or absence of, the 

 nerve-cord can be demonstrated only by more direct proof. It must be 

 shown (i) that regeneration did not take place, even though the amputated 

 region was re-innervated by the regenerated nerve-cord ; (2) that regenera- 

 tion could take place without any trace of the nerve-cord in the region 

 adjoining the amputated level. This proof was obtained by a detailed 

 examination of serial longitudinal sections of posterior pieces. Table 5 in- 

 cludes the 46 posterior pieces from which the nerve-cord had been remo\ed 

 and which were subsequently preserved 25 to 30 days later. ^ 



Tadle 5. 



Out of 28 worms, 7 regenerated a distinct head; the other 21 did not 

 regenerate in the same interval. Worm number 33 is typical of the 7 

 operated worms which regenerated their heads. The serial sections showed 

 that the nerve-cord had been completely removed from the seven segments 

 nearest the amputated level, agreeing with the record made at the time of 

 operation. It was found that typical ganglia of the nerve-cord extended 

 as far as the middle of the sixth segment from the amputated level, at 

 which point the nerve-cord suddenly became narrow and extended in this 

 very narrow, partially ganglionated condition into the fifth, fourth, third, 

 second, and first segments, beyond the amputated level into the regener- 

 ated head. It continued dorsally and ended finally in a clearly differ- 

 entiated supra-oesophageal ganglion. The details are identical with those 

 described elsewhere^ for Liinihricus. These worms afford no clue to the 

 dependence or independence of regeneration upon the presence of the 

 nerve-cord at the amputated level, nor of the manner in which the central 

 nerve system was formed. 



The second group of operated worms did not regenerate the head. I 

 have arbitrarily designated a regenerated head one in which at least the 

 stomadeum and "brain" were clearly differentiated. Worm number 32 

 may serve as an example of this group. In this worm the characteristic 



> The high mortality occurred chiefly in worms operated by the "window" method of removing the nerve-cord. 

 ^Goldfarb, A. J., I'uie. 



