The two principal conditions on which climatal causes generally may be said to rest, are latitude and altitude. As regards the former of these, however, whilst the equatorial and arctic regions of the earth will of course give us the extremes of heat and cold, we shall often perceive differences of temperature (the result perhaps of local circumstances) in areas but slightly removed from each other, sufficient to affect very materially, though by what means it is difficult to understand, the outward contour of the insect tribes. Thus, to go no further than Ireland, we find that the specimens of _Silpha atrata_, Linn., so abundant throughout England and the whole of Europe, have put on (it may be from the moisture of the atmosphere, or from some other obscure influence) the appearance of a distinct race,--so distinct indeed as to have long received another name, _S. subrotundata_, from British naturalists. I think it far from improbable that the _Tachyporus nitidicollis_, Steph., an insect eminently characteristic of that country (and one on which I have lately offered some remarks[7]), is but a darker climatal modification of the common _T. obtusus_: and it is well known that the examples of _Pelophila borealis_, Payk., from Killarney and Loch Neagh are permanently larger, and much more metallic, than those from the Orkneys. The _Nebria complanata_, Linn., assumes a more pallid hue in the neighbourhood of Bordeaux than it does on the sandy coasts of Devonshire and Wales: and I have but little doubt that the _Omaseus nigerrimus_, Dej., of Spain, the north of Africa, and Madeira, is a geographical state of the _O. aterrimus_ of Central Europe. The _Sitona gressoria_, Illig., so universal throughout the Mediterranean districts, Madeira and the Canaries, may be but the subaustral form of _S. grisea_. The _Bembidium obtusum_, Sturm, is shorter and less parallel in our own latitude than it is in the Madeiran group and along the Mediterranean shores: whilst the _Holoparamecus niger_, Aube, of Madeira and Sardinia is very much paler than the same beetle when taken in Sicily. Specimens of _Pieris Brassicae_, Linn. (the White Cabbage-Butterfly,--an insect of widely acquired range), from Nepaul and Japan, are recorded[8] to have differed so strongly from the ordinary European type as to have been referred, by Boisduval, in doubt to that species. Mr. Westwood has received the _Vanessa Atalanta_, Linn., from North America, receding slightly from its British analogue; but which he, nevertheless, does not regard as specifically distinct: and such also (he adds) was the opinion of Mr. Kirby, who has described his American examples under that name. The common _Hipparchia_ of Madeira I believe to be a fixed geographical modification of the _H. Semele_, Linn., of our own country,--in which the paler bars of the upper surface are evanescent;--there are, however, I imagine, but few entomologists who would concur with me in this hypothesis.