No one can have examined large series of any species without being impressed with the modification of patterns in almost every possible way. For instance, we have reared quantities of _Papilio Machaon_, and find great differences, not only in the pattern, but in the colour itself. A number of pupæ from Wicken Fen, Cambridgeshire, were placed in cages, into which only coloured light could fall, and though these experiments are not sufficiently extended to allow us to form any sound conclusions as to the effect of the coloured light, we got more varieties than could be expected from a batch of pupæ from the same locality. The tone of the yellow, the quantity of red, the proportion of the yellow to the blue scales in the clouds, varied considerably, but always along the known and established lines. The variations in the colour of Lepidoptera has been most admirably treated by Mr. J. Jenner Weir in a paper, only too short, read before the West Kent Natural History Society.[33] He divides variations into two sections, Aberrations or Heteromorphism, and constant variations or Orthopæcilism, and subdivides each into six classes, as under:-- _Heteromorphism._ Albinism ... ... white varieties. Melanism ... ... black do. Xanthism ... ... pallid do. Sports ... ... or occasional variations not included in the above. Gynandrochomism ... females coloured as males. Hermaphroditism ... sexes united. _Orthopæcilism._ Polymorphism ... variable species. Topomorphism ... local varieties. Atavism ... ... reversion to older forms. Dimorphism ... ... two constant forms. Trimorphism ... ... three do. do. Horeomorphism ... seasonal variation. In some cases, he remarks, variations are met with which may with equal propriety be classed in either section. Albinism he finds to be very rare in British species, the only locality known to him being the Outer Hebrides. This reminds us of Wallace's remark upon the tendency to albinism in islands. Xanthism, he finds to be more plentiful, and quotes the common Small Heath (_Cænonympha pamphilus_) as an illustration. In these varieties we have simply a bleaching of the colouring matter of the wings, and therefore no departure from structural lines. Melanism arises from the spreading of large black spots or bars, or, as in _Biston betularia_, a white moth peppered with black, dots by the confluence of small spots; for this insect in the north is sometimes entirely black. It is singular that insects have a tendency to become melanic in northern and alpine places, and this is especially the case with white or light coloured species. (_See_ Plate IV., Fig. 17) It has recently been suggested that this darkening of these delicate membranous beings in cold regions is for the purpose of absorbing heat, and this seems very probable.[34]