MONOUIIAPH OF THE EXISTING CKINOIDS. 693 



nules responded. Complete recoveiy of these specimens resulted when, after a 

 few moments, they were again placed in water at 28°. 



Individuals placed in water at SC jrave no responses and failed to recover : they 

 became quite rigid. 



Doctor Clark remarks that these exjieriinents show that, as compared with the 

 comatulids of Maer Island, Trop'wmetra plcta has a susprisingly large temperature 

 range. This is quite in keeping with their habitat in Buccoo Bay, for while the 

 water there probably never falls below 22° C, there is no doubt that at the lowest 

 tides it rises in the shallows to 32°, and possibly to 34°. Even should it on rare 

 occasions exceed this figure for a short time the animals would easily survive. 

 Owing to the comatulids' inertness it was impossible to determine the optimum 

 temperature. 



In water of 33° reactions were not consistently different from what they were 

 at 25°. Nevertheless, individuals in water at 33° assumed a .somewhat wilted 

 appearance after a time, which was not the case in water at 28° and lower. 



Healthy individuals gave no response to a sudden change of 2°, but there was 

 generally an evident reaction to an abrupt change of .5°. 



RESPONSE TO CHEMICAL STIMULI. 



Dr. H. L. Clark found that the response of the comatulids he studied at Maer 

 Island. Torres Strait, to a strong solution of magnesium sulphate was prompt 

 and violent, so violent as to break off some or all of the arms, and no evidence of 

 ■^ub.sequent relaxation was found. 



Alcohol poured onto the disk of a crinoid in the tank brought about a verj' 

 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 droj^ped into alcohol or formalin 

 the response was immediate, and consisted in the extreme flexion of the arms 

 dorsally. Often this would be followed by strong oral or ventral flexion, bringing 

 the arms up vertically over the mouth. This again would be followed by a general 

 relaxation, and later 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 with each other and with the cirri dorsally, but sometimes closed together 

 over the mouth. 



Doctor Clark says that owing to the fact that almost without exception the first 

 response is flexion dorsally it is very easy to prepare perfectly expanded specimens. 



The animals are lifted from the sea water with the cirri down and pluneed 

 abruptly into strong alcohol in ;i shallow flat dish, care being taken to press the 

 animal down at once to the bottom of the dish. The dorsal flexion causes the arms 

 to lie out flat against the bottom of the dish. The following ccmtraction of the 

 ventral muscles is occasionally strong enough to bring the arms up over the disk 

 and to get them badly entangled, but in the very great majority of cases it is so 

 feeble and so quickly followed by relaxation that a little manipulation of the arms. 



