222 THE APODID^: PART n 



the Trilobites, chiefly through the patient researches of 

 Walcott, they are still shrouded in a certain amount of 

 mystery. We believe that it will be found that our 

 derivation of the Trilobites from a bent Annelid will 

 throw considerable light upon the beautiful series of 

 sections made by Walcott, by giving a new clue to 

 the interpretation to be put upon them. 



One difficulty, for instance, which has been found 

 in classifying the Trilobites with the Crustacea is the 

 absence of any trace of limbs (i.e. of antennae) in front 

 of the mouth. This, however, from our point of view 

 is no real difficulty. In reality the antennae of Apus 

 are hardly in front of the mouth but in a line with 

 it, and both are more or less rudimentary, from being 

 caught in the angle of the bend. This same bend was 

 equally sharp in the Trilobites (see Fig. 46). Why 

 may not the antennae have been in this bend, and as 

 rudimentary as they are in Apus ? We shall try to 

 answer this question in the following pages. 



We have, in Walcott's restoration (see Fig. 50), 

 posteriorly to the labrum, three small limbs with mas- 

 ticatory processes, followed by a large pair of loco- 

 motory limbs with especially large ventral parapodia 

 for mastication. For reasons given above (pp. 44, 190) 

 we homologisc these large locomotory limbs with the 

 sixth pair of typical Crustacean limbs, i.e. with the 

 first pair of trunk limbs. The three pairs of limbs 

 anterior to these are therefore homologous with the 

 mandibles and the two pair of maxillae of the typical 

 Crustacean head. In front of these and behind the 

 labrum, we have, in Walcott's restoration (Fig. 50), a 



