506 PROF. J. E. DUERDEN ON CRABS [DeC. 12, 



a result 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 vigorovis move- 

 ments 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 noi- any from the crab. In fact, throughout the 

 observations the actinians and crabs responded or remained in- 

 difierent to the same substances ; in each case ingestion reflexes 

 took place only towards nutritive substances from which stimula- 

 tive 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 ab- 

 sti-action on the part of the crab, we may assume that the nuti-itive 

 juices were so weak tha,t they failed to reach the sensory organs 

 of the crab, and thereby failed to stimulate it to activity. 



POLTDECTUS. 



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 conti-ast 

 with Melia. The former is very hairy, sluggish, and ii'responsive, 

 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 sui'face 

 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 



