Thus the first subsection presents us with the brush-legged _Apidæ_ (_Scopulipedes_), which collect pollen upon their posterior legs. These are further subdivided into those which collect it upon the whole limb, viz. the coxa, the femur, the tibia, and first joint of the tarsus, (the _femoriferæ_), and those which gather it merely upon the shank and basal joint of the foot (the _cruriferæ_). These collectively form a well-defined group, and why _Panurgus_ should be separated from the brush-legged bees, when it is a most conspicuous instance of the faculty, even more so than any other of the _Scopulipedes_, I have yet to learn. It is true its mode of collecting closely resembles that practised by the _Andrenidæ_, as does also the furniture for the purpose of its posterior legs, but being essentially collocated with the _Apidæ_ or normal bees by its tongue, it fittingly links itself to the other brush-legged _Apidæ_ (which have hitherto been placed between the _Dasygasters_ and the Social Bees), by means of the genus _Eucera_, by reason of its two submarginal cells, the structure of its maxillary palpi, its mode of burrowing, and by each being infested by a similar parasite—a _Nomada_, which in accommodation to the size of the sitos is the largest of the genus. _Nomada_ does not occur as a parasite upon any other of the brush-legged bees, or indeed upon any other of the true bees at all, which peculiarity brings these two genera into close contiguity to all non-parasitical _Andrenidæ_, all of which have their legs furnished with polliniferous brushes, and upon which subfamily, exclusively of these two instances of _Panurgus_ and _Eucera_, _Nomada_ is solely parasitical. With respect to the two submarginal cells to the wings, nature must have some reason for the limitation, for we find it prevalent also throughout the _Dasygasters_, or hairy-bellied bees. The next very natural group is consistently central. It comprises the cuckoo-bees, which are naked-legged (_Nudipedes_), by reason of their parasitism, they not requiring organs to collect what they have no occasion to use. Their parasitism extends both upwards and downwards, those with three submarginal cells being parasitical upon all the brush-legged bees, whether subnormal _Andrenidæ_ or the _Scopulipedes_, those with two submarginal cells being restricted in their parasitism to the _Dasygasters_.