NERVOUS SYSTEM OF ANTEDON ROSACEUS. 537 



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 which 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 de- 

 struction 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 connec- 

 tion 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. 



As the radial cord (fig. 3) divides into the two axial cords 

 before entering the Third Radial, the sole anatomical connection 

 between the axial cords of the two arms in the above experi- 

 ment is afforded by the transverse commissure and the chiasma, 



