B. By a consideration of the following laws the age of a division can be approximately arrived at; that is to say, its position in the great genealogical tree of the _Lepidoptera_ can be, to some extent, determined:-- "(1) No new organ can be produced except as a modification of some previously existing structure. "(2) A lost organ cannot be regained. "(3) A rudimentary organ is rarely redeveloped."--(Meyrick.) {xvii}C. The greatest care is necessary to avoid being misled by adaptive characters, _i.e._, characters which are very important to the welfare of the species, and hence much modified through the agency of natural selection. A familiar instance of superficial resemblance, due to the presence of similar adaptive characters, may be observed in fishes and whales, where two groups of animals with but little real relationship have, through living under similar conditions, become extremely like each other in external appearance. Other examples might be given amongst exotic _Lepidoptera_. Thus, many noxious species are closely mimicked by harmless forms which are often far removed from them in real affinity. These cases of adaptive resemblances abound amongst all organisms, and have often deceived experienced naturalists. It is in consequence of the illusive nature of these external resemblances amongst different members of the _Lepidoptera_, that the structure of the neuration of the wings is now considered of such great importance as a character for purposes of classification. The numerous modifications in the position of the veins and their presence or absence in certain groups can, so far as we are able to see, have had very little effect on the well-being of those insects possessing such modifications. Hence it may fairly be assumed, that these structures have been free from the influence of natural selection for a very lengthened period. It is thus contended that the neuration of a Lepidopterous insect probably reveals more plainly than any other character its true relationship with other species. The descent of all the _Lepidoptera_ from some ancient member of the _Trichoptera_ (or caddis-flies) is thus proved, according to Mr. Meyrick:--