12 INTRODUCTION 



Phytogeny. 



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



From a consideration of the laws enunciated above, there 

 can be no doubt that the Micropterygina are the ancestral 

 group of the Lepidoptera, from which all others have descended ; 

 this is sufficiently proved by the existence of the four or more 

 additional veins in the hindwings 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 more 

 primitive than the Hepialidae. Now if the neuration of the 

 whole of the Lepidoptera is compared with that of all other 

 insects, it will be found that in no instance is there any close 

 resemblance, except in the case of the Micropterygidae ; but 

 the neuration of these so closely approaches that of certain 

 Trichoptera (caddis-flies) as to be practically identical. The 

 conclusion is clear, that the Lepidoptera are descended from 

 the Trichoptera, and that the Micropterygidae are the true 

 connecting link. If the other marked structural characters of 

 the Micropterygidae are taken into consideration, viz., the 

 possession of the jugum, the large development of the maxillary 

 palpi as compared with the labial, and the sometimes functionally 

 active mandibles, they will be all found commonly in the Trichop- 

 tera, affording additional confirmation. It may be added that 

 in one exotic (New Zealand) species of Micropterygidae, vein Ib 

 is basally trifurcate, a character frequent in the Trichoptera, 

 but not yet discovered in any other Lepidopteron. In most 

 Trichoptera the veins of the hindwings are much more numerous 

 than those of the forewings, in the Micropterygina they are 

 usually equal in number, in other Lepidoptera they are less 

 numerous ; in the course of descent there has therefore been a 

 greater progressive diminution in the number of veins of the 

 hindwings as compared with those of the forewings, though 

 these have also diminished. 



It is unnecessary for the purposes of this book to trace back 

 the descent of the Lepidoptera further ; lout it may be worth 

 while to point out that we may assume as the primitive type of 

 Trichopterous neuration, a system of numerous longitudinal 

 veins 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. 



