. . and asrudimentary as they are in Apus ? We shall try toanswer this question in the following pages. We have, in Walcotts 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 parapodiafor mastication. For reasons given above (pp. 44, 190)we homologise these large locomotory limbs with thesixth pair of typical Crustacean limbs, with thefirst pair of trunk limbs. The three pairs of limbsanterior to these ar
. . and asrudimentary as they are in Apus ? We shall try toanswer this question in the following pages. We have, in Walcotts 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 parapodiafor mastication. For reasons given above (pp. 44, 190)we homologise these large locomotory limbs with thesixth pair of typical Crustacean limbs, with thefirst pair of trunk limbs. The three pairs of limbsanterior to these are therefore homologous with themandibles and the two pair of maxillae of the typicalCrustacean head. In front of these and behind thelabrum, we have, in Walcotts restoration (Fig. 50), a SECT. XI IF THE TRILOBITES space in which we think the antennae should havebeen drawn. That they were present we have littledoubt, probably somewhat reduced, as in Apus, andpointing backwards. Our reasons for thinking thatthere must have been two pairs of antennae as here de-. FIG. 50.—Ventral surface of Calymene Senaria restored by Walcott (from Zittel).Assuming that the large pair of locomotory limbs are the sixth or first trunklimbs. The two pairs of antennae are missing—they should probably be drawnin on each side of the prostomium projecting backwards, as in Apus. scribed, are two, apart, that is, from the general reasonsfounded upon our theory of their relationship to Apusthrough common descent from a bent Annelid. (i.) Figs. 51 and 52 are sections passing throughthe prostomium (labrum or hypostoma) of two Trilo- 224 THE APODID^: PART 11 bites. In the second of these they are cut throughalong the line shown in Fig. 53. These transversesections through the head and labrum certainly seemto indicate the presence of such antennae as we havedescribed, at least they seem to show that there wereappendages of some sort starting out sideways fromeach side of the labrum, just as in Apus. It isp
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