SECT. XIII THE TRILOBITES 233 



The question as to whether the leaf-Hke feet per- 

 sisted at the hinder end of the body is an interesting 

 one. We have no certain data on the subject, but, 

 from our point of view, we do not think it at all 

 probable. We have seen that in Apus even the most 

 rudimentary limb repeats the Phyllopodan type. We 

 are also inclined to believe that the more rudimentary 

 Trilobite limbs would naturally repeat the Trilobite 

 ambulatory type. The presence of flat leaf-shaped 

 limbs in the Euryptcridai and Limulus, accompanied 

 by highly specialised anterior limbs, may perhaps be 

 used as an argument in favour of their presence in 

 the Trilobitcs also. On the other hand the highly 

 developed gills on the trunk limbs of the Trilobites 

 rendered it unnecessary to concentrate respiration on 

 a few broad gills at the posterior end of the body as 

 in Eurypterus and Limulus, which in this respect 

 compare with some modern Isopoda. 



The first trunk limb, according to Walcott's 

 restoration, has both its locomotory dorsal branch 

 and its masticatory ventral branch specially strongly 

 developed (see Fig. 50). It is, in some respects, very 

 natural that the masticatory ridge of a powerful 

 locomotory limb, if it possessed any function at all, 

 should gradually come to be the chief jaw, as we 

 shall see to have been the case also in the Eury- 

 pteridaj ; the disadvantages of this arrangement will, 

 however, be pointed out later. 



We have already shown why the first trunk limb, 

 being the parapodium of the first free segment, not 

 taken up in the formation of the head, should be 



