56 Mr Borradaile, On the Functions of the Mouth-Parts etc. 



On the Functions of the Mouth-Parts of the Common Prawn. 

 By L. A. Borradaile, M.A., Selwyn College. 



[Read 30 October 1916.] 



The food is seized by either pair of chelipeds, or by the 

 third maxillipeds, and is usually placed by them within the 

 grasp of the second maxillipeds, though sometimes it is passed 

 directly to deeper-lying structures. The second maxillipeds are 

 the most important of the food-grasping organs. They have three 

 principal movements; in one, the broad flaps in which they end 

 open downwards like a pair of doors, and with their stout fringes 

 gather up the food ; in another, they rotate in the horizontal plane 

 to and from the middle line of the body, and thus narrow or widen 

 the gap through which the food passes; in the third, the bent distal 

 part of the limb tends to straighten, so as to brush forward any 

 object which lies between them. Frequently these movements are 

 combined. Owing to the facts that the second maxillij)eds cover 

 the mouth-parts anterior to them, and that if they be removed 

 feeding is not properly performed and usually not attempted, it is 

 difficult to trace the food beyond them, but the following seems to 

 be its fate. If it be small in bulk, or finely divided, or very soft, 

 it is passed to the maxillules, by whose strong, fringed laciniae it is 

 swept forwards, and probably caused to enter through the slit 

 between the paragnatha, into the chamber which is guarded by 

 the upper and lower lips. If it be tough or in large masses, the 

 second maxillipeds and maxillules brush it forwards towards the 

 incisor processes of the mandibles. The action of the latter is, by 

 rotating in a vertical plane, to tuck the food into the gap between 

 the paragnatha and the labrum. If the mass be large, pieces are 

 torn off it by this action. Finally, to enter the gullet, the food 

 must pass between the molar processes and be pounded by them. 



The mandibular palps, maxillae, and first maxillipeds appear 

 to play parts of little importance in regard to the food. The 

 palps are present and absent in closely related genera, and appear 

 to be disappearing in the higher Carides. The same is true of the 

 lobes of the maxillae, which are in constant regular motion to and 

 from the middle line, and probably serve to restrain the action of 

 the scaphognathite. The large laciniae of the first maxilliped 

 may have as their function the covering of the maxillae and 

 protecting them from the food. The labrum undergoes active 

 movements, whose function is probably to aid in keeping the 

 food under the action of the mandibles. The exopodites of the 

 maxillipeds set up a strong current forwards from the mouth. 

 No doubt this aids in carrying away the exhausted water from 

 the gill chamber and the excreta from the tubercles of the green 

 glands. Into the same current particles which have been taken 

 as food are from time to time rejected by the forward kicking 

 of the second maxillipeds. 



