118 Papers from the Department of Marine Biology. 



RESPONSE TO OTHER STIMULI. 



Mechanical stimuli met with ordinary response under normal con- 

 ditions. The disk and the pinnules at the bases of the arms seem to 

 be more sensitive to touch than either the middle or terminal part 

 of the arms. The cirri and the whole aboral surface are slow to respond 

 to mechanical stimulation. The response to touching the disk is a 

 closing of the arms over it and the response to touching the oral 

 surface of an arm is the gradual infolding of that arm. Mechanical 

 stimulation alone, even a severe pinch of an anterior arm with forceps, 

 seldom caused any change in the direction of locomotion. The net 

 result of all the observations was the impression that comatulids are 

 surprisingly callous to mechanical stimuli, and the response is never 

 sudden or hurried. 



It was particularly desirable to determine if comatulids showed a 

 quick response to changes of salinity in the sea-water, but the results 

 of the experiments were all negative. There was no success in securing 

 any response to the addition of rain-water to the sea-water in the 

 aquaria, even when the rain-water was poured directly onto the disk 

 of the crinoid. The transfer of a comatulid from sea-water directly 

 to rain-water met with marked response and violent movements, but 

 as long as the water in the tank was predominantly salt, there was 

 no visible response to the addition of rain-water. On the other hand, 

 the increase of salts seemed to be a matter of equal indifference, but 

 the response to a strong solution of magnesium sulphate was prompt 

 and violent. This is the more remarkable because the reaction is so 

 different from that shown by starfishes and ophiurans. When these 

 echinoderms are thrown into a saturated solution of magnesium sul- 

 phate, there is a brief period of activity, but not violent, and this is 

 followed by complete stupefaction and relaxation of the whole mus- 

 cular system. Comatulids, however, respond to the stimulation of 

 the solution so violently as to break off some or all of the arms and 

 no evidence of subsequent relaxation was found. This peculiarity of 

 muscular reaction in comatulids deserves much more careful study 

 than circumstances at Mae'r permitted. 



Alcohol poured on the disk of a crinoid in the tank brought about a 

 very marked response, but the latent period was surprisingly long 

 and the effect of the stimulus soon wore off. If comatulids were taken 

 from sea- water and dropped into alcohol (or formalin), the response 

 was immediate and consisted in the extreme contraction of the arms 

 aborally (L e., backwards). Often this would be followed by a strong 

 oral contraction, bringing the arms up vertically over the mouth. 

 This again would be followed by a general relaxation followed by death 

 and a hardening of the tissues. Specimens simply thrown into alcohol 

 (or formalin) or placed in the fluid, mouth down, never died in a 

 natural position, the arms being strongly contracted, usually entangled 



