338 THE INVERTEBRATA 



food. It is known as the gnathobase. The most distal " endite " is the 

 termination of the corm, and is better called the "apical lobe". It 

 has often special functions. The number of the endites varies. In the 

 Branchiopoda it is commonly six, but in the Anostraca (Fig. 238) 

 there are indications of seven. It is greatest in the larval maxilla of 

 certain decapoda (Fig. 222 A), where it is nine, which, as we have 

 seen, is the maximum number of segments in the corm of the steno- 

 podium. The suggestion, made by this fact, that the segmentation of 

 the phyllopodium by endites corresponds with that which the corm 

 of the stenopodium owes to the presence of joints, is strengthened by 

 the fact that in some of the maxillae in question (Fig. 222 B), and in 

 that of Calanus (Fig. 251), which also has nine segments, the limb is 

 jointed and the joints fall between the endites or, where these are 

 lacking, precisely complete their number. A less regular jointing of 

 the same kind is present in some other phyllopodia (Apus, Fig. 224 ; 

 etc.). In both kinds of limb, also, the position of the exopodite bears 

 the same relation to the segmentation, being usually upon the third, 

 occasionally upon the fourth segment, while epipodites stand on the 

 first or second segment. Endites are rare on stenopodia, but a 

 gnathobase is always present in the mandible (Fig. 222 D) and some- 

 times in other limbs, and a few other such processes occur. 



A limb of either type may differ from that type in the lack of any 

 of its parts. Notably the loss of the exopodite is liable to produce 

 from either a uniramous limb. Moreover, though the two types are 

 very distinct in cases in which they are perfectly developed, as in the 

 swimmerets of Astacus (Fig. 222 G) and the trunk limbs of Apus 

 (Fig. 224), there are many limbs which depart more or less from 

 either type in the direction of the other — as, for instance, from the 

 stenopodial type in the shape of the exopodite (Fig. 254 B), or, as 

 stated above, in the relation of the latter to the rest of the limb, or 

 from the phyllopodium in the proportions of the rami or the reduction 

 of the endites. 



The comparison just made between the phyllopodium and the 

 stenopodium leaves untouched the question which of them is the 

 more primitive, that is, more resembles the limbs of the ancestral 

 crustacean. On this point there is an old and as yet unsettled con- 

 troversy. As proof of the primitiveness of the stenopodium it is 

 pointed out (i) that this limb is more widespread than the phyllo- 

 podium, (2) that it occurs in the Nauplius larva (p. 352), the early 

 phyllopod Lepidocaris (p. 360), and the trilobites, in all of which it 

 is likely to be primitive, (3) that it more nearly approaches the form 

 of the majority of parapodia of the Annelida, from which the Crus- 

 tacea are held to have taken origin. In demonstration of the ancestral 

 nature of the phyllopodium it is urged (i) that typical stenopodia 



