and a vein once lost can never be regained; but of course the loss may have, and apparently has, taken place independently in more than one line of descent. The whole of the remaining Lepidoptera may then be classed in two groups (Psychina and Pyralidina) which normally retain this vein, and four others which have entirely lost it.
The Psychina are a group of families of unspecialized type, which in fact approach the Tineina so closely as not to be separable as a whole by any single character, though each family considered by itself is so separable; at the same time the four families composing it are nearly related together in their lowest forms, and may therefore be regarded as parallel developments. Even the markings of the wings show this want of specialization, as they are, when present, irregular and without definite type of arrangement, and all the families show a marked tendency (in the Psychidæ becoming a fixed character) to produce thinly-scaled or semi-hyaline unicolorous forms. It is probable that this indicates approximate relationship to the Fumea group of the Tineidæ, to which the Psychidæ also display their affinity by their apterous females and the case-bearing habit of the larva; on this ground they have even been included together in the same family, but the true Psychidæ are always distinguished by the anastomosing subdorsal veins of the fore wings. The Zygænidæ include many large butterfly-like forms, brilliantly coloured with metallic blue, crimson, and white; the short, stout, often tuberculated and rather hairy larvae are of an early type, and though apparently very different in form and habits to the Psychidæ, both are probably the modified descendants of internal wood-feeders. The Heterogeneidæ (Limacodidæ of some) are remarkable for their larvæ, which are an exaggeration of the Zygænid type, the legs being often very short and retractile, so that the larva appears to be appressed to the leaf like a slug, whilst the dorsal tubercles are often developed into clusters of stinging spines; and for the small hard oval cocoons, which open by a lid. The tibial spurs of the imago are long, as in the Tineina generally, whilst in the allied families they are very short or absent, but there is here probably some connection with bulk or weight. Finally, the Zeuzeridæ, whilst structurally related to the Psychidæ, show by the wood-feeding habit of their larvæ and other characters
