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Show 506 PROF. J. E. DUERDEN ON CRABS [Dec. 12, a l'esult of stimulation by the meat juices emanating from the food on the disc. Fragments of meat or meat extract diffused around the anterior part of the crab called forth vigorous movements of the mouth-appendages and first pair of walking-legs, though directed towards no very definite end; but when the extract was applied towards one side or the other, there was a decided movement of the appendages in that direction. Similarly, juices emanating from the food on the polypal disc may be assumed to serve as the stimuli by which the reflexes are brought about, the source of the stimulation and direction of response being determined from the direction in which the juices reach the crab. When non-nutritive particles, such as fragments of shell or grains of sand, were placed upon the polypal disc they produced no movements on the part of the actinian ; likewise there was no response from the crustacean. Also in other cases substances which called forth no responses on the part of the actinian failed to bring about reactions from the crab. A small spider fallen into the water, and thereby drowned, was given the actinian. The tentacles closed over it momentarily, then withdrew, leaving the spider exposed on the disc. In this case the crab made no attempt to abstract the spider from the polyp, and after a time it was rejected by the latter. Fragments of bread and small pieces of paper placed on the polypal disc called forth no response from the actinian nor any from the crab. In fact, throughout the observations the actinians and crabs responded or remained indifferent to the same substances; in each case ingestion reflexes took place only towards nutritive substances from which stimulative juices might be supposed to emanate, while there was indifference or rejection towards what might be supposed to be non-nutritive substances. Where the food supplied was so small in bulk that the polyp ingested it without any attempt at abstraction on the part of the crab, we may assume that the nutritive juices were so weak that they failed to reach the sensory organs of the crab, and thereby failed to stimulate it to activity. POLYDECTUS. While searching among the blocks of coral rock for further examples of Melia, a single specimen of Polydectus cupilifera (Latr.) was secured, also bearing an actinian in each claw. Both in its form and behaviour the new crab presented a great contrast with Melia. The former is very hairy, sluggish, and irresponsive, while the latter is active and most readily responds to stimuli of all kinds. The actinians held by Polydectus were small specimens of a species of Phellia, which occurs in abundance on the under surface of rocks and stones all round the Hawaiian Islands. Externally the polyps are characterised by having a thick cuticle over the greater part of the column, a circular area at the apex (the |