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Reactions to Certain Chemicals

comatulids and amount

REACTIONS TO CERTAIN CHEMICALS.

Although no experiments were made to test the reactions to chemi cals, it may be worth while to record the observations made in other connections. Indifference to the amount of in the water was noticeable, particularly in view of the sensitiveness of Torres Strait comatulids to that substance. As already stated, 2 specimens lived over night in only 2 liters of sea-water, apparently without discomfort, and 4 or 5 specimens were often kept over night in aquaria with not more than 6 or 7 liters. Unlike the comatulids tried in Torres Strait, Tropiometra when fresh from the sea responds to a saturated solution of in sea-water, like other echinoderms, the whole muscular system becoming relaxed. The response was much less complete if the individual had been for some time in a limited amount of sea water; probably the presence of made the difference. Response

to alcohol and formalin was, as in other comatulids, by a contraction first of the dorsal side of the arms and then of the ventral. Only exceptionally, and then by individuals which had been long in tank or aquaria, were the arms cast off.

Summary.

The common habitat of Tropiometra at Tobago, Buccoo Bay, is unusual for a crinoid, the bottom being covered with coralline algae and eelgrass, the water shallow, and the comatulids exposed to the full glare of the tropical sun.

Reactions to light, temperature, salinity, and

all show Tropio metra to be remarkably insensitive and hardy. It shows only feeble phototactic reactions, has a temperature range of at least 15° C., a salinity range well over 40 per cent, and withstands a considerable but undetermined amount of without injury.