FEEDING, LOCOMOTION AND RESPIRATION 2 1 



wards; this results in further extrusion of water from the inter-limb 

 space. Now the limbs are not just simple flaps, but are thicker along 

 the middle of their length than near the inner and outer edges. 

 This means that when the limbs are pressed close together the inter- 

 limb space is divided into two parts, and water can only escape 

 from the inner part by going back into the median space. There 

 is a small, forwardly directed groove near the base of each limb 

 which allows water to escape from the inner part of the inter-limb 

 space. The spurt of water at the end of a backstroke thus blows 

 food particles in the basal part of the food groove towards the 

 mouth. 



Food particles are also removed from the filter setae by another 

 method. As two successive limbs move forwards the setae of the 

 front limb will be sucked back against the inner edge of the limb 

 behind and against the body wall at the base of that limb. Both 

 the inner edge of the limb and the body wall at its base are provided 

 with fine setae which project between the filter setae of the limb in 

 front and comb food particles into the median space, where they 

 can be blown towards the mouth by the spurts of water from the 

 inner parts of the interlimb spaces at the end of a backstroke. 



Food is moved forwards in the midline until it reaches the level 

 of the second maxillae, where it becomes entangled in a secretion 

 from the large glands in the labrum. The maxillules push the sticky 

 mass into the mouth. 



The important features to note about the anostracan method of 

 feeding are: (i) all the thoracic limbs are involved in both swim- 

 ming and feeding, (2) food is passed forwards in the midline 

 between the limbs, and (3) there is a large labrum which secretes a 

 viscous fluid to consolidate the food before it is swallowed. 



Feeding and locomotion have become separated in the Con- 

 chostraca. The feeding mechanism is similar in its basic feature to 

 that of the Anostraca, but the limbs are enclosed in a carapace, 

 and the current flowing out from the inter-limb spaces cannot be 

 used for swimming. The branched antennae take over this function, 

 and have well-developed muscles which are not present in the 

 Anostraca. A further complication in the Conchostraca is that some 

 of the hind limbs do not act as filters, but have strong spines on 

 the inner sides of their bases. These spiny bases can act as jaws 

 and break up larger food particles than can be collected by the 

 normal filtering mechanism. As these larger particles are broken 

 up they are passed slowly forwards from the base of one limb to 



