Is it not time to abandon these fanciful expectations which are never realised? Everywhere both among animals and plants does the problem of specific difference reiterate itself in the same form. In view of such facts as I have related and might indefinitely multiply, the fixity of specific characters cannot readily be held to be a measure of their economic importance to their possessors. The incidence of specific fixity is arbitrary and capricious, sometimes lighting on a feature or a property which can be supposed to matter much, but as often is it attached to the most trifling of superficial peculiarities. The incidence of _variability_ is no less paradoxical, and without investigation of the particular case no one can say what will be found to show much or little variability. The very characteristic which in one species may exhibit extreme variability may in an allied species show extreme constancy. Illustrations will occur to any naturalist, but nowhere is this truth more strikingly presented than in the British Noctuid Moths. Many are so variable that, in the common phrase, "scarcely two can be found alike," while others show comparatively slight variation. It need scarcely be remarked that, in the instances I have in mind, the evidence of great variability is in no way due to the abundance with which the particular species occurs, for common species may show constancy, and less abundant species may show great variability. The polymorphism seems to be now at least a general property of the variable species, as the fixity is a property of the fixed species. In illustration I may refer to the following examples. _Dianthoecia capsincola_ is a common and widely distributed moth which feeds on _Lychnis_. It shows little variation. _Dianthoecia carpophaga_ is another species which feeds chiefly on _Silene_. Its habits are very similar to those of _capsincola_. Like that species it has a wide geographical range and is abundant in its localities, but in contrast to the fixity of _capsincola_, _carpophaga_ exhibits a complex series of varieties. _Agrotis suffusa_ (= _ypsilon_) is a moth widely spread through the southern half of England. It is very constant in colour and markings. _Agrotis segetum_ and _tritici_ are excessively variable both in ground colour and markings, being found in an immense profusion of dissimilar forms throughout their distribution. Of these and several other species of _Agrotis_ there are many named varieties, some of which have by various writers been regarded as specifically distinct. Of the genus _Noctua_ many species (e. g. _festiva_) show a similar polymorphism, but _N. triangulum_, though showing some variation in certain respects, is usually very constant to its type, and the same is true of _N. umbrosa_.