350 SYDNEY J. HIOKSON. 



The yellow variety owes its colour to a pale yellow tiut iu 

 the spicules, which is retained after the colony is dead and 

 preserved in spirit. 



When first brought on deck from the dredge or trawl, the 

 colonies are of a soft, flabby consistency, with the extensible 

 portion of the polyps retracted, but still visible as transparent 

 circles on the surface. If a colony be allowed to remain out 

 of water for some little while the transparent circles become 

 smaller and smaller, until at last only a star-shaped depression 

 is left to indicate the position of the polyps. At the same 

 time the colony itself contracts considerably until it reaches 

 a size not much more than two thirds of its original bulk. 



When the colonies are placed in a sea-water aquarium they 

 soon regain their former size by the absorption of water, and 

 in a few hours the polyps expand. The colonies, however, 

 do not, if they remain in a healthy condition, continue ex- 

 panded indefinitely, but are seen to contract and remain 

 contracted for some time at intervals. These periodic con- 

 tractions are quite independent of light, but as a rule seem to 

 be synchronous with tide intervals, — that is to say, they occur 

 twice in every twenty-four hours. 



My experiments at Plymouth, two years ago, proved that 

 for the first three or four days after capture they contracted 

 regularly twice in every twenty-four hours, but after that their 

 times of contraction became irregular. 



A number of experiments were tried with some Alcyoniums 

 placed in a tank in which an artificial tide, rising and falling 

 only once in twenty-four hours, was introduced, and at the 

 end of a fortnight I found that the two colonies which re- 

 mained healthy were contracting regularly only once in twenty- 

 four hours. 



My observations were not sufficiently satisfactory to enable 

 me to draw any general conclusions from them, but they seem 

 to indicate that there is a normal rhythmic contraction of the 

 polyps of Alcyonium corresponding with some state of the tides 

 — probably low water, and that a new rhythm may be induced 

 by an artificial tide of difiFerent duration from the normal one. 



