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INTRODUCTION

Phylogeny.

This term is used to express the scheme of descent of a group.

From a consideration of the laws enunciated above, therecan be no doubt that the Micropterygina are the ancestralgroup of the Lepidoptera , from which all others have descended ;this is sufficiently proved by the existence of the four or moreadditional veins in the hind wings of that group, for these veins,if not originally present, could not have been afterwards pro-duced. Of the two families of that group, the Micropterygidae,which possess an additional vein (or veins) in the forewings,and fully-developed six-jointed maxillary palpi, must be moreprimitive than the llepialidae. Now if the neuration of thewhole of the Lepidoptera is compared with that of all otherinsects, it will be found that in no instance is there any closeresemblance, except in the case of the Micropterygidae; butthe neuration of these so closely approaches that of certainTrichoptera (caddis-flies) as to be practically identical. Theconclusion is clear, that the Lepidoptera are descended fromthe Trichopitera, and that the Micropterygidae ai'e the trueconnecting link. If the other marked structural characters ofthe Micropterygidae are taken into consideration, viz., thepossession of the jugum, the large development of the maxillarypalpi as compared with the labial, and the sometimes functionallyactive mandibles, they will be all found commonly in the Trichop-tera. , affording additional confirmation. It may be added thatin one exotic (New Zealand ) species of Micropterygidae , vein lbis basally trifurcate, a character frequent in the Trichoptera,but not yet discovered in any other Lepidopteron. In mostTrichoptera the veins of the hindwings are much more numerousthan those of the forewings, in the Micropterygina they areusually equal in number, in other Lepidoptera they are lessnumerous; in the course of descent there has therefore been agreater progressive diminution in the number of veins of thehindwings as compared with those of the forewings, thoughthese have also diminished.

It is unnecessary for the purposes of this book to trace backthe descent of the Lepidoptera further; but it may be worthwhile to point out that we may assume as the primitive type ofTrichopterous neuration, a system of numerous longitudinalveins gradually diverging from the base, mostly furcate ter-minally, and connected by a series of irregularly placed cross-bars near base, and another series beyond middle.