The two common British wasps, _Vespa vulgaris_ and _Vespa germanica_, are another pair of species closely allied although sharply distinguished, which suggest similar reflexions. Both usually make subterranean nests but of somewhat different materials. _V. vulgaris_ uses rotten wood from which the nest derives a characteristic yellow colour, while _V. germanica_ scrapes off the weathered surfaces of palings and other exposed timber, material which is converted into the grey walls of the nest. The stalk by which the nest is suspended (usually to a root) in the case of _germanica_ passes freely through a hole in the external envelope, but _vulgaris_ unites this external wall solidly to the stalk. In bodily appearance and structure the two species are so much alike that they have often been confounded even by naturalists, and to the untrained observer they are quite indistinguishable. There are nevertheless small points of difference which almost though not quite always suffice to distinguish the two forms. For example the yellow part of the sinus of the eyes is emarginate in _vulgaris_ but not emarginate in _germanica_. _V. vulgaris_ often has black spots on the tibiae while in _germanica_ the tibiae are usually plain yellow. In both species there is a horizontal yellow stripe on the thorax, but whereas in _vulgaris_ this is a plain narrow stripe, it is in _germanica_ enlarged downwards in the middle. These and other apparently trivial details of colouration, though not absolutely constant, are yet so nearly constant that irregularities in these respects are quite exceptional. Lastly the genitalia of the males, though not very different, present small structural points of distinction which are enough to distinguish the two species at a glance.[14] In considering the meaning of the distinctions between these two wasps we meet the old problem illustrated by the Sparrows. The two species have somewhat different habits of life and we should readily expect to find differences of bodily organisation corresponding with the differences of habits. But is that what we do find? Surely not. To suppose that there is a correspondence between the little points of colour and structure which we see and the respective modes of life of the two species is perfectly gratuitous. We have no inkling of the nature of such a correspondence, how it can be constituted, or in what it may consist.