V.—CLASSIFICATION, NOMENCLATURE AND REMARKS. 
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CHAPTER V. 
CLASSIFICATION, NOMENCLATURE AND GENERAL REMARKS. 
If we admit the principles of organic evolution briefly 
explained in Chapter IV., it is clear that all existing species 
must have descended by true generation from pre-existing 
species, and that all the relationships we observe between 
organisms are explained by community of origin. The most 
natural system of classification is therefore one which re- 
veals most clearly the scheme of descent, or the phylogeny 
of the group of organisms classified. In consequence, how- 
ever, of the great number of species which are at present 
unknown to naturalists, and the greater number which have 
become extinct, the problem of framing, even approxi- 
mately, a phylogenetic system of classification is one of very 
great difficulty, and the conclusions of even the most ex- 
perieneced workers must, therefore, be accepted with a con- 
siderable amount of reservation. 
In considering the value of characters for purposes of 
classification, those which are constant and prevalent are 
of the greatest importance, especially if they have no direct 
bearing on the welfare of the species. Adaptive characters, 
or those which have been much modified by natural selection, 
are of little value as they necessarily fail to indicate real 
relationship. Thus in the eases of mimicry, already con- 
sidered, adaptation through natural selection has brought 
about numerous superficial resemblances between species of 
insects which have no real affinities. 
It is in consequence of the illusive nature of these ex- 
ternal resemblances amongst different members of the 
Lepidoptera, that the structure of the neuration of the 
wings is of such great importance as a character for pur- 
poses of classification. Except where the shape of the en- 
tire wing has been modified the numerous variations in the 
positions of the veins and their presence or absence in cer- 
tain groups can, so iar as we are able to see, have had 
very little effect on the well-being of the insects possessing 
them. Henee it may fairly be assumed, that these struc- 
tures have been free from the influence of natural selection 
for a very lengthened period and 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. 
As already indicated resemblances between all organ- 
isms are explained by community of origin, the amount of 
difference representing the amount of modification and cx- 
pressible in the classification as varieties, species, genera, 
families, orders, &e. The amount of difference does not 
necessarily bear any direct relation to time, many forms 
remaining almost stationary whilst others are undergoing 
development. 
By a consideration of the following laws, which are 
generally recognised by systematists, the age of a division 
can be approximately arrived at; that is to say, its position 
in the great genealogical tree of life 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). 
As an example of the application of the above prin- 
ciples, I have much pleasure in quoting the following in- 
teresting remarks by Mr. Meyrick, respecting the origin of 
all the Lepidoptera from some ancient member of T'richop- 
tera or Caddis-flies :-— 
‘There ean be no doubt that the section comprising 
the two families Hepialidae and Microplerygidae is 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 hind-wings of 
that group, for these veins, if not originally present, could 
not have been afterwards produced. Of the two families 
of that group, the Micropterygidae, which possess an ad- 
ditional vein (or veins) in the fore-wings, and fully 
developed six-jointed maxillary palpi, must be more primi- 
tive 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 Microptery- 
gidae; but the neuration of these so closely approaches 
that of certain Trichoptera (eaddis-flies) as to be practi- 
eally identical. The conclusion is clear, that the Lepidop- 
tera 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 
*At the present time some entomologists have adopted two 
main divisions for the Lepidoptera:— 
1. The Homoneura, including those species in which the 
neuration of the fore- and hind-wings are practically 
identical; and 
2. The Heteroneura, including those in which the fore-wings 
have 12 veins and the hind-wings 8 veins. 
No doubt this division of the order, which has long been 
recognised, is a natural one, and of considerable phylogenetic 
significance, but it is of little practical use in classifying the 
order as a whole, seeing that such a vast preponderance of the 
species belong to the Heteroneura. The Homoneura are exactly 
equivalent! to the Micropterygina of Meyrick, and the Heteroneura 
to the rest of the Lepidoptera. See Handbook of British Lepidop- 
tera (1895) pages 12 and 797. 
**That is from some insect which, if now living, would be 
classed as Trichopterous. 

