FEEDING MECHANISM 439 



shell. Food particles carried on this stream will be abstracted by the grasping action 

 of the mandibles. The latter are bent double at the level of the exopodite so that the 

 tips reach back to the mouth. Dolorta is probably capable of foraging on the bottom 

 as does the common British Cypridinid Cyltfidroleberis oblonga. In this case, since the 

 mandibles can be projected beyond the edges of the valves, food would be kicked up 

 by their tips in the same manner as function the antennae of P. vidua. Such particles 

 would be sucked into the shell cavity by the inhalent stream. 



Food is thus gathered or sucked into the shell just underneath the labrum. The 

 immense labral glands open in this region. Their secretion is, of course, the origin of 

 the luminescence of certain Cypridinids. However, it also undoubtedly functions as a 

 food-entangling substance as in the case of P. vidua, and enables the mandibles to pass 

 the entangled mass backwards on to the maxillules. The latter are bent double just 

 as are the mandibles but, in this case, the "knee", which occurs between basipodite 

 and coxopodite, points outwards so that the tips of the limbs can be rotated inwards 

 and upwards towards the mouth. These tips are formed by the massive endopodites, 

 and are situated some distance below the actual mouth. In P. vidua the maxillules 

 work together in the middle line immediately at the mouth entrance and, with the help 

 of the food rakes arming the back of the mouth, pass the food directly on to the mandibles 

 which are on the same level. In Doloria, the food mass has to be lifted up by the tips 

 of the maxillules and deposited on the actual biting parts at the mouth entrance. The 

 latter are formed by the three endites of the maxillule and the endites and part of the 

 exopodite of the maxilla, which work in series with one another. All are armed with 

 complex powerful spines which have been described in great detail by Skogsberg 

 (1920, p. 225). The armature of the first endite of the maxillule is in a line posteriorly 

 with that of the second endite of the maxilla, the second with that of the third and 

 the third with the main tooth of the exopodite of the maxilla. 



The food entering the shell is thus entangled in the labral gland secretion, passed 

 backwards by the mandibles on to the endopodite of the maxillule, and lifted up on 

 to the complex biting spines on the more proximal parts of the maxillules and maxillae, 

 where it is triturated. 



While this is happening the food mass must be continually subjected to the antero- 

 posterior current passing through the shell. This is counteracted by the first trunk 

 limbs. The setae of the endites of these limbs extend forwards so as to lie actually 

 between the biting setae of the maxillae. The musculature suggests that the limbs move 

 backwards and forwards, thus continually pushing the food mass on to the biting parts. 

 Even if the limbs did not move they would form an effective barrier to food particles. 



Similarly the powerful setae on the second exopodite joint of the maxilla project 

 obliquely forwards, and must serve to push any particle which happens to reach them 

 on to the tips of the maxillules and so to the biting parts. 



The inward movement of the grinding mouth-parts has a slight upward component 

 which is enhanced by the tendency of the spines to slope upwards, and this results in 

 the food mass, during trituration, passing upwards towards the mouth. 



