The essential fact that the two types of limb are built on the same plan may be considered as established; but it may be urged that the biramous type represents this common plan more nearly than the foliaceous. It is, at any rate, certain that in the maxillipedes of the Decapoda we witness the conversion of the biramous type into the foliaceous by the expansion of the basal joints concomitantly with the assumption by the maxillipedes of masticatory functions. Thus in the Decapoda the first maxillipede is decidedly foliaceous owing to the expanded “gnathobases” (Fig. 1, A, _bp_, _cxp_), and the second maxillipedes are flattened, with their basal joints somewhat expanded and furnished with biting hairs; but in the “Schizopoda” (_e.g._ _Mysis_) the first maxillipede is a typical biramous limb, though the expanded gnathobases in some forms are beginning to project (Fig. 1, E), while the limb following, which corresponds to the second maxillipede of Decapods, is simply a biramous swimming leg. Besides this obvious conversion of a biramous into a foliaceous limb, further evidence of the fundamental character of the biramous type is found, first, in its invariable occurrence in the Nauplius stage, which does not necessarily mean that the ancestors of the Crustacea possessed this type of limb in the adult, but which does imply that this type of limb was possessed at some period of life by the common ancestral Crustacean; and, second, the limbs of the Trilobita, a group which probably stands near the origin of the Crustacea, have been shown by Beecher to conform to the biramous type (Fig. 1, H). Furthermore, the thoracic limbs of Nebalia, an animal which combines many of the characteristics of Entomostraca and Malacostraca, and is therefore considered as a primitive type, despite their flattened character, are really built upon a biramous plan (Fig. 1, G). In conclusion, we may point out that this view of the Crustacean limb, as essentially a biramous structure, agrees with the conclusion derived from our consideration of the segmentation of the body, and points less to the Branchiopoda as primitive Crustacea and more to some generalised Malacostracan type.