MOUTH-PARTS OF THE PALiEMONIH PRAWNS. 



69 



vertical. This arrangement, combined with the presence of a 

 fringe of bristles along the inner edge of the limb, has the effect 

 of forming a kind of basket below the month- region, walled in at 

 the sides by the ischiomeropodites and by the bristles which 

 project downwards and inwards from their edges. In Leander * 

 there are bristles borne in a diagonal row along the ventral 

 surface of the ischiomeropodite, and also upon ridges of the 

 coxopodite, basipodite, and ischiopodite of the first leg (text- 

 fig. 51), which complete the basket behind and below, but these 

 are less w T ell developed or absent in Ponton time. In front of the 

 mouth, the distal parts of the third maxillipeds, with their 

 bristles, afford a surface, horizontally placed below the antennal 

 region while the appendages are outstretched, which by bending 

 can be brought ventrally under the mouth so as to complete its 

 enclosure anteriorly. The last joint often possesses along its 

 inner side a thick brush composed of tufts of hairs more close-set 

 than the bristles of the rest of the limb. This arrangement, 

 which is particularly well developed in Leander, has probably 

 some special function, but I have not been able to discover what 

 that may be. 



IY. 



1. It is not an easy matter to induce Leander to feed at a given 

 moment, and still less so to observe what it is doing while it feeds. 

 The animal will not take food if it is not hungry, if it is languid 

 owing to lack of aeration of the water, or if it is suffering from 

 shock, though sometimes it will feed surprisingly soon after 

 violent operations, such as the removal of limbs. I have tried to 

 observe the action of its jaws by means, of a mirror, but without 

 much success. The best method is to fasten the prawn upon its 

 back in a shallow vessel of sea water by means of plasticine. It 

 will often feed quite freely in this position, and its jaws can easily 

 be reached with a needle. When it is feeding, small particles of 

 food may be seized by the chelipeds of either pair, and by them 

 conveyed to the mouth, where they are generally received by the 

 second maxillipeds, though sometimes they appear to be placed 

 directly in charge of more dorsally placed structures, probably 

 the maxillules. A large morsel occasionally appears to be steadied 

 by the legs of the second pair, while those of the first tear off 

 fragments and carry them to the jaws, but it is more often placed 

 as a whole within the grasp of the second maxillipeds, which 

 hold it in place while pieces are torn off it by deeper-lying organs, 

 probably in the main by the incisor processes. In handling bulky 

 masses of food, the chelipeds are assisted by the third maxillipeds, 

 which bend back their last two joints for this purpose. The third 



* In this genus, in which the bristles of the third maxilliped are best developed, 

 there may be made out three bands along the limb — an inner, middle, and outer, 

 perhaps corresponding to the marginal, submarginal, and lateral of the four series 

 found by Claus in Nebalia (text-fig. 8, p. 42). Each band consists of a succession 

 of little transverse rows. Towards the ends of the appendage the bands converge 

 and become merged. 



