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



to stimuli take place in a Melia depi-ived of its actinians as when 

 they are present, but the empty chelipecls make no attempt what- 

 ever to grasp the source of irritation as in ordinary crabs. The 

 movable joint (dactylopodite) remains partly open, to about the 

 same degree as when holding an actinian, and its use as an 

 organ for direct protection or attack seems to have altogether 

 disappeared. 



The responses of the chelipeds are manifestly so many instinctive 

 reflexes on the part of the crab, directed towards the region whence 

 the irritation comes, and are <;arried out independently of the 

 presence or absence of the actinians. When the latter are in 

 position, the reactions may be assumed to be aggressive or pro- 

 tective in their nature ; while when taking place in the absence 

 of the polyps they are of no protective value, as the claws are 

 useless for grasping or seizing. 



Compared with most crabs, it would seem that there is in MeUa 

 a marked increase in the power of directive response on the part 

 of the chelipeds, accompanied by a loss of activity on the part of 

 the movable joint which ordinarily sei-vesfor aggressive purposes ; 

 moreover, the chelipeds as a whole are greatly reduced in size. 



Feeding Reactions. 



Under ordinary circumstances, the Melias were often seen trans- 

 ferring towards their mouth the debris occurring on the bottom 

 of vessels or other objects over which they passed. This they 

 accomplished by means of the maxillipeds, with the assistance of 

 the first, second, and even third pair of ambvilatory limbs, the 

 first ambulatory pair being the most active. The debris was 

 seized by the maxillipeds, and the nutritive particles were ingested, 

 and the non-nutritive rejected and wafted away posteriorly. The 

 chelipeds, whether empty or holding actinians, took no part 

 whatever in the feeding processes. Even fragments of meat given 

 directly to the crab w^ere treated in the same manner ; their 

 passage to the masticatory appendages was effected by the first 

 ambiilatory limbs, always without the assistance of the chelipeds. 



As the a,ctinians were dragged about from place to place, debris 

 readily adhered to them by means of the viscid slime with which 

 they were covered, and very frequently the first ambulatory limbs 

 were applied to the polypal walls, and the latter were thoroughly 

 cleansed from any adhering particles. The operation was carried 

 out much in the same way as that by which the crab cleansed its 

 own limbs. During the process the actinians were brought close 

 to the mouth, and the d6bris removed was easily transferred 

 thereto by the appendages. Some of the particles were nutritive, 

 and there is no question that the crab will frequently secure food 

 material thus mechanically adhering to the walls of tlie polyp. 

 No instance was observed where the crab applied its appendages 

 to the general body-surface of the polyps except when foreign 

 partides were adherent. During the cleansing treatment the 



