MORGULIS. — REGENERATION IN THE BRITTLE-STAR. 657 



imposed upon the other ; they are usually designated as ectoneural and 

 hyponeural systems. There are in addition many ganglia and an elab- 

 orate peripheral system of nerves, but we shall not be concerned with 

 the latter. 



The operation consisted in destroying a small portion of the radial 

 nerve in order to break its connection with the ring-nerve, and was 

 performed in the following manner : The calcareous plate on the oral 

 surface of an arm was first punctured with a needle (see Figure ^4) a 

 very short distance from the disc. In this way an opening was estab- 

 lished leading into the canal in which the nerve lies. If released at 

 this phase of the operation, the animal would crawl away, using all 

 its arms, and behaving in an absolutely normal fashion, showing thus 

 that the injury was not serious. Next, a red hot needle was introduced 

 into the opening already made, burning the nerve at that particular 

 spot, as will be seen from the diagram. To prevent the needle from 

 injuring the deeper portions of the arm, its point was bent at an angle 

 of 45°. After this operation the animal would crawl away, but would 

 use only the uninjured arms, while the injured arm would be practically 

 paralyzed and curled up about the point of injury, being dragged along 

 passively. In nearly all cases when the wound was not made deep the 

 arm was not cast off even at the end of thirty days, when the animals 

 were preserved. Whenever the wound was made too deep, the arms 

 were subsequently cast off. 



When this preliminary operation had been accomplished, the arm was 

 cut off at about the middle of its length. In a number of animals an- 

 other arm with the nerve intact was also cut off at about the middle, 

 this serving as a control for the arm with an injured nerve. In every 

 case the arms with the radial nerve intact regenerated from the cut sur- 

 face, and so far as I could ascertain, they regenerated quite normally. 

 On the other hand, if the radial nerve was injured before cutting off 

 the arm, 2 the latter in the course of thirty days regenerated only a 

 small stump, which might easily be overlooked unless the specimen 

 were examined closely. Figures 1 to 5 of the Plate represent several 

 brittle-stars in all of which the same results appear. Where the radial 

 nerve was left intact, a long new part was regenerated (Plate, Figures 1, 

 3, and 5), whereas if the nerve was destroyed near the disc, so little new 

 tissue was formed that it is difficult to recognize it at all. The in- 

 teresting thing in this connection, however, is that in cases where the 

 animal threw off the arm at the place of injury to the nerve, there 

 was absolutely no regeneration from the cut surface thus produced 



2 The place of injury to the nerve is indicated by a cross in Figures 1 to 5. 

 vol. xliv. — 42 



