FEEDING, LOCOMOTION AND RESPIRATION 31 



anostracan method of feeding, but there are certain fundamental 

 differences. It is true that the niters are carried on the inner borders 

 of the thoracic limbs and that food is trapped in the median space 

 between the two rows of limbs. But there the resemblance ends. 

 The legs are arranged so that when they move they suck in water 

 from in front of the animal and pass it out backwards. Food 

 trapped by the filter setae is passed forwards by groups of brush-like 

 setae which project from one limb to the next in front, and as the 

 limbs move in relation to each other the food is transferred towards 

 the mouth (fig. 22). 



PATH OF FOOD 



pfifmciE cpugmt 

 BY brush sera 



A B 



Fig. 22. A, Trunk limb of Nebalia (Leptostraca). The brush setae 

 project obliquely forwards from the inner margin of the limb. 

 B, Diagram showing the way in which the brush setae move food 

 particles forwards towards the mouth. (B, after Cannon, 1927). 



Larger particles are trapped before they enter the space between 

 the limbs and are bitten into by the spiny bases of the maxillules. 

 When a large mass accumulates near the maxillules the palps of 

 the mandibles can be bent backwards and push the food into the 

 mouth to be subjected to the crushing action of the main body of 

 the mandible. 



A further complication is found in the deep water plankton form 

 Nebaliopsis, which is regarded as a more specialised relative of 

 Nebalia. The thoracic limbs of Nebaliopsis appear to produce a 

 current in the opposite direction from that produced by Nebalia. 

 This has been deduced from a study of preserved specimens, but 

 the analysis seems quite reasonable. The current flows forwards, 



