SECT. XIII THE TRILOBITES 225 



possibility of using the parapodia as instruments for 

 pushing food into the mouth ; and indeed, whether 

 our theory is correct or not, we doubt if any case 

 will be found of a Crustacean mouth without limbs 

 as mouth parts closely bordering it. Walcott's restora- 

 tion, given in Fig. 50, is therefore so far incomplete. 

 The mouth, which is covered by the large labrum, must 

 have had some kind of appendages bordering it on 

 each side. When therefore we find clear traces of such 



Fi<;. 52.— Sections of Calymene Senaria (after Walcott) passing through the prosto- 

 mium, showing traces of limbs springing out from each side of the same, whicli 

 we assume to he homologous with the antennae of Apus ; the fragments of limbs 

 at the sides may be those of trunk limbs brought near the mouth by the rolling 

 up of the animal. The section passes along the line shown in the ne.xt 

 figure. 



limbs in the sections (Figs. 51, 52), we think we are 

 justified in claiming them as such. 



It will no doubt be objected that these two reasons 

 are only sufficient to show that there were limbs as 

 mouth parts on each side of the mouth, near the 

 labrum, but not that they were the homologues of the 

 Crustacean antennae. This homology depends, it is 

 true, upon the truth of our main argument that the 

 Trilobites, like Apus, were originally bent Annelids, 



