THE NERVOUS SYSTEM OF ANTEDON ROSACEUS. 287 



several arms. Figs. 1 and 3 show that the pentagonal commissure, 

 which is lodged in the First Radials, would not be touched by the 

 operation, and, as it furnishes an anatomical connection between 

 the axial cords, it was naturally suspected to be the physiological 

 connection as well. To test this the following experiment was made : 



Experiment 21. — The same specimen employed in the preceding 

 experiment was taken, and the inside of the canal surrounded by the 

 First Radials freely painted with nitric acid, until the pentagonal 

 commissure was exposed and destroyed. The animal was then returned 

 to the water and left for half an hour on its oral face, where it 

 remained without any attempt to right itself or to swim. The arms 

 were then strongly nipped with forceps one by one ; each arm when 

 irritated responded by active movements, but none of the other arms 

 stirred except the other arm of the pair to Avhich the irritated arm 

 belonged, which moved sometimes slightly, sometimes actively. 



This last observation shows that there is a physiological connection 

 between the two arms of each pair still remaining after the several 

 pairs are isolated from one another by destruction of the pentagonal 

 commissure. There is, as we have seen, an anatomical connection in 

 the Third Radial (fig. 3), and the following experiments were made 

 to test whether this furnishes also the physiological connection in 

 question. 



Experiment 22. — A pair of arms was cut off a specimen, the section 

 passing between the First and Second Radials. After half an hour's 

 interval one of the arms was stimulated, when both arms moved 

 actively. 



Experiment 23. — Another specimen was eviscerated and a pair of 

 arms removed, the section passing between the Second and Third 

 Radials (cf. fig. 3). All the soft parts were scraped from the basal 

 portions of the arms, the basal pinnules were cut off, and the Third 

 Radial and basal joints of the arms freely scraped and painted with 

 nitric acid, so that the sole connection between the two arms was 

 through the substance of the Third Radial. After half an hour one 

 of the arms was sharply nipped ; the irritated arm moved freely, and 

 the other arm slightly but distinctly. The experiment was repeated 

 with a second specimen, and an interval of three hours allowed 

 between the operation and stimulation of the arm. In this case active 

 and extensive movements of both arms followed on irritation of either 

 one 4 



