xii CRUSTACEA 159 



are much fused in the thoracic region, though still distin- 

 guishable. The carapace is thought to correspond to thirteen 



anti 



FIG. 95. The Common Prawn (appendages of one side only shown). 



anti, First antenna; ant%, second antenna; mxp^, third "jaw foot"; l v to Z 5 , five 



" walking legs " ; S, swimmerets. 



segments, and thirteen pairs of appendages spring from 

 below it. 



Attached to the soft cuticle between the ventral 

 and lateral portions of the exo-skeleton are the 

 limbs or appendages, one pair to each segment ; 

 these are much modified in different regions of the body to 

 suit the function they have to perform (Fig. 96). 



The head region of the carapace is separated from the 

 thoracic region by a transverse groove on the back ; it bears, 

 besides the stalked eyes, two pairs of long feelers or antennae. 

 Surrounding the mouth, which lies right below the head, are 

 also the modified appendages known as the "mouth-parts." 

 These consist here of one pair of hard biting jaws or mandibles, 

 and two pairs of leaf -like "soft jaws" or maxillae, which 

 perhaps help in the subdivision of the food before it enters the 

 mouth. These first five pairs of appendages belong to the 

 five segments of which the head is thought to be formed. 



The first three pairs of thoracic legs are turned forward, 

 and they also lie on the lateral borders of the mouth; they 

 aid in passing the food into the mouth, and are therefore 

 termed "jaw feet" (maxillipedes). The first two pairs 

 of these jaw feet are much modified, and their basal joints 

 aid in the division of the food, but the last pair far 

 more closely resembles the remaining legs of the thorax. . 



