Proceedings, 191 5. 105 



" Certain other considerations may likewise be of assistance. A 

 large genus, especially if also of very wide distribution, cannot be a very 

 recent one, since it must have required a long period for the differen- 

 tiation of numerous species, though it must be remembered that as the 

 genus grows larger the process may become more rapid from increased 

 basis of production. On the other hand, a small genus may be of any 

 age ; but one which is closely related to a large genus will almost always 

 be later than it, and a small genus which is widely distributed must 

 generally be an old one. 



" In applying the above-mentioned laws in practice, it must be 

 constantly borne in mind that because two genera are now more 

 closely allied together than to any other, it does not follow that -either 

 is descended from the other ; it is very frecjuently the case that both 

 are equally derived from a third genus now no longer existent. In 

 such a case they are said to be correlated. Further, when one genus 

 is said to be derived from another, and the earlier genus is rich in 

 species, it is not usually meant that the later genus springs from the 

 more advanced forms of the earlier one, but much more commonly from 

 a species standing very near the bottom of the list. 



" From a consideration of the laws enunciated there can be no 

 doubt that the Micropterygina are the ancestral group of the Lepidop- 

 tera, from which all others have descended. This is sufficiently proved 

 by the existence of the four or more additional veins in the hind-wings 

 of that group, for these veins, if not originally present, could not have 

 been afterwards produced. 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 Micropter)^gidse; 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 Micropterygidje are the true connecting-link. 

 It may be worth while to point out that we may assume as the primitive 

 type of trichopterous neuration a s}'Stem of numerous longitudinal veins 

 gradually diverging from the base, mostly furcate terminally, and con- 

 nected by a series of irregularly placed cross-bars near the base, and 

 another series beyond middle." 



Before I leave this phase of the subject, it is instructive to know 

 what Professor Comstock has written with regard to the descent and 

 relationship of the various orders of insects. Fie divides the class 

 Hexapoda into nineteen- orders. He says: — ■ 



" The Th3-sanura (bristle-tails, spring-tails, fish-moths, and others) 

 is doubtless the most primitive order. Then follow first the orders that 

 undergo an incomplete metamorphosis, and last, those that undergo a 

 complete metamorphosis. \\'ithin these two orders those with biting 

 mouth-parts are placed first, and these are followed by those with suck- 

 ing uKiuth-parts, except that in the second group the Coleo]itera and 



