698 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



effect followed irritation of one of the ordinary pinnules, while irritation of the 

 oral pinnules caused immediate and strong flexion of all the arms. 



Experiment 3. An active specimen vras eviscerated and allowed to come to 

 rest in the normal position. It was then inverted and placed mouth downward 

 on the bottom of the tank. After a short rest it righted itself in the normal man- 

 ner, but rather more slowly than usual, the interval between inversion and the 

 completion of the righting being about two and a half minutes. 



This experiment was repeated many times with different specimens. Some 

 righted themselves instantaneously, others took a longer or shorter tune, but the 

 general average of the times taken by eviscerated specimens to right themselves 

 was about half a minute longer than that of uninjured ones. 



Experiment 4- A. specimen was eviscerated and allowed to come to rest. A 

 needle was Ihen passed from the oral surface down the canal within the radials 

 so as to irritate the central capsule. The result was immediate flexion of the arms, 

 and in many cases active swimming movements of the whole animal. 



Experiment 5. A specimen was eviscerated and then cut into two parts, one 

 having two pairs of arms and the other three. The central capsule, which was 

 divided and freely exposed by the operation, was then irritated by a needle. The 

 slightest irritation caused very active and violent flexion of the arms. 



Experiment 6. An active uninjured specimen was held under water and the 

 dorsal half of the centrodorsal plate removed by a single snip with a large pair 

 of scissors, so as to expose and partly remove the central capsule. On being 

 released the animal fell to the bottom with the arms very strongly extended, but 

 in about 20 minutes gradually righted itself and assumed the normal position. 

 The exposed central capsule was then irritated, first with a needle and then with 

 strong nitric acid applied by a small brush. The effect of irritation was to cause 

 very strong and spasmodic flexion of the arms, which in the first case ceased on 

 removal of the stimulus, but in the case of the acid persisted for several hours. 



Experiment 7. The centrodorsal of an active specimen was removed with 

 scissors and the central capsule carefully scooped out with a small scalpel. The 

 animal on being released fell to the bottom of the water, where it lay on its side 

 with the arms very strongly extended, remaining in this position for several hours 

 without any attempt to move. If taken from the water and thrown in again the 

 arms moved fairly actively, but there was no attempt at swimming, each arm 

 apparently acting quite independently of the rest. Finally, if placed on its oral 

 surface, it remained there for an indefinite time without making the slightest 

 attempt to right itself. 



Experiment 8. The preceding experiment was repeated on an eviscerated 

 specimen, the results being in all respects the same. 



To obtain definite results in these experiments it is necessary to remove com- 

 pletely the central capsule, and this Marshall found could not be effected by simply 

 cutting away the centrodorsal plate ; in addition, the capsule must be either scraped 

 out with a fine scalpel or else destroyed by free painting with strong acid. 



Specimens in which the centrodorsal plate has been simply snipped off, though 

 they lose temporarily the power both of swimming and of righting themselves, 



