340 PERCY SLADEN TRUST EXPEDITION 



inwards and rotating upwards. No doubt during this the food undergoes some tearing, 

 and when the mass is large pieces have to be torn off it before they can be swallowed. 

 The palp does not appear to take any mechanical part in the process. If it has a sensory 

 function this is probably not of great importance, for the organ is present and absent 

 in closely related genera in many cases among Carides. Finally, to enter the gullet, 

 the food must pass between the molar processes, and be pounded by them as it goes. 

 Their concave ends are usually found to be clogged with a pasty matter. They must 

 do their work very quickly, for the movement of the mandibles, as judged by that 

 of the incisor processes, ceases very soon after the food leaves the latter. How swallowing 

 takes place is not clear. Parker and Mocquard suggest that the food of Decapod 

 Crustaceans is caused to pass up the gullet by suction from the crop (stomach), but, 

 as I have shown elsewhere*, the case of the land hermit-crabs of the genus Coenobita 

 throws doubt upon this explanation. It may be that the constrictor muscles of the 

 oesophagus play some part in the process. 



The first maxillipeds and the maxillae probably take no very prominent part in 

 manipulating the food. The feeble lobes of the maxillae are in incessant movement 

 to and from the middle line as they are carried inwards and outwards by the action 

 of the scaphognathite. It seems likely that their sole function is to regulate the motions 

 of the latter. The large lacinia of the first maxilliped is a rather feeble structure 

 with slender, silky bristles, and is not strongly moved during feeding. Probably, by 

 covering the lobes of the maxilla, it prevents them from being clogged by the food. 



The part played by the paragnatha seems to be a passive one. The labrum 

 undergoes active movements whose function is probably to aid in keeping the food 

 under the action of the incisor processes. 



The exopodites of the maxillipeds are in constant rapid motion, setting up by 

 their activity a strong current forwards from the mouth. No doubt this assists in 

 carrying away the foul water from the gill chambers and the excreta of the green 

 glands poured out at the base of the antennse. But it has also a significance in the 

 feeding process. From time to time particles are rejected by the second maxillipeds, 

 which kick them violently forwards, the distal parts of the third maxillipeds at the 

 same time straightening so as to admit them to the outgoing stream, by which they 

 are swept away. 



It has already been stated that the mouth-parts of the Pontoniinae, even in the 

 most decidedly commensal species, are not highly modified as compared with those 

 of the free-living Palaemoninee. For such modifications as exist it is, however, possible 

 to suggest a connection with the nature of the food. The broad third maxillipeds seem 

 better adapted to shepherd a crowd of minute organisms than narrower types of those 

 organs, and the large, hairy laciniae of the maxillules of the Pontonia group perhaps 

 serve the same purpose. 



The legs of the first pair are chelate, but relatively slender and never of great 

 length. They are alike and equal. Their chelae are usually of simple form, but in 



* Gardiner's Fauna of the Maldives, i. p. 79 (1901). 



