From a further consideration of the foregoing principles it will be seen
that all existing species are held to be descended by true generation from
pre-existing species, and that, consequently, all the relationships we
observe between species are explained by community of origin. The most
natural system of classification is, therefore, that which best reveals the
scheme of descent, or, as it is termed, the phylogeny, of the group of
organisms classified. To construct a perfect system of classification on
these principles a knowledge of not only all the existing species of
_Lepidoptera_ would be essential, but also of all the extinct species, and
it is needless to say that such knowledge is quite unattainable.
Nevertheless large numbers of species are now known from many parts of the
world, and a very extensive collection has recently been employed by Mr.
Meyrick in framing a classification of the _Lepidoptera_, which is, to the
best of my belief, the first constructed on strictly Darwinian principles.
Although adopting Mr. Meyrick's system in the present work I do not agree
unreservedly with all his conclusions; but I have not attempted to alter
his system in accordance with my own views, as I conceive that the
conclusions of a naturalist, who has only had the opportunity of studying a
restricted fauna, would necessarily be liable to considerable error.
The general principles on which Mr. Meyrick has founded his system are
practically those laid down by Darwin in his 'Origin of Species,' and may
be thus summarised:--
A. Resemblances between all organisms are explained by community of origin,
the amount of difference representing the amount of modification and
expressible in the classification as varieties, species, genera, families,
groups, orders, &c. The amount of difference does not _necessarily_ bear
any direct relation to time, many forms remaining almost stationary whilst
others are undergoing development.
B. By a consideration of the following laws the age of a division can be
approximately arrived at; that is to say, its position in the great
genealogical tree of the _Lepidoptera_ 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.)
{xvii}C. The greatest care is necessary to avoid being misled by adaptive
characters, _i.e._, characters which are very important to the welfare of
the species, and hence much modified through the agency of natural
selection. A familiar instance of superficial resemblance, due to the
presence of similar adaptive characters, may be observed in fishes and
whales, where two groups of animals with but little real relationship have,
through living under similar conditions, become extremely like each other
in external appearance. Other examples might be given amongst exotic
_Lepidoptera_. Thus, many noxious species are closely mimicked by harmless
forms which are often far removed from them in real affinity. These cases
of adaptive resemblances abound amongst all organisms, and have often
deceived experienced naturalists. It is in consequence of the illusive
nature of these external resemblances amongst different members of the
_Lepidoptera_, that the structure of the neuration of the wings is now
considered of such great importance as a character for purposes of
classification. The numerous modifications in the position of the veins and
their presence or absence in certain groups can, so far as we are able to
see, have had very little effect on the well-being of those insects
possessing such modifications. Hence it may fairly be assumed, that these
structures have been free from the influence of natural selection for a
very lengthened period. 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.
The descent of all the _Lepidoptera_ from some ancient member of the
_Trichoptera_ (or caddis-flies) is thus proved, according to Mr. Meyrick:--
"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 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
_Micropterygidæ_, which possess an additional vein (or veins) in the
fore-wings, and fully developed six-jointed maxillary palpi, must be more
primitive than the _Hepialidæ_. 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 _Micropterygidæ_; 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 _Micropterygidæ_ are the true connecting link.
If the other marked structural characters of the _Micropterygidæ_ 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 _Trichoptera_, affording additional confirmation. It may be added that
in one New Zealand species of _Micropterygidæ_ (_Palæomicra chalcophanes_)
vein _1b_ 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
fore-wings, 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 hind-wings as compared with those of the fore-wings, though these
also have diminished.
{xviii}"It is unnecessary to trace back the descent of the _Lepidoptera_
further; but 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
terminally, and connected by a series of irregularly placed cross-bars near
base, and another series beyond middle."
The following is Mr. Meyrick's method of arrangement, which has been
adopted in this book:--
"The natural order of arrangement, which is that of a much-branched tree,
cannot be adequately expressed by a simple linear succession, such as is
alone practicable in a book. It is, however, possible to devise a linear
succession which shall be consistent with the natural genealogical order,
if some additional explanation can be given. The method here adopted is as
follows:--
[Illustration]
"Suppose the accompanying diagram represents a portion of the genealogical
tree; then the order will begin at M and descend to K, recommence at L and
descend to K, and thence to G, recommence at H and descend to G, and thence
to B, recommence at F and descend to D, recommence at E and descend to D
and thence to B, recommence at C and descend to B and thence to A, and so
on. Thus the order begins with the most recently developed forms and
descends gradually to the earliest or most ancestral, which are the last in
the book. To understand the order in practice, it may be assumed that each
genus is descended from that which immediately follows it in the book,
unless its actual descent is expressly stated otherwise; such statement
will, of course, require to be made before every recommencement of a fresh
branch. This system has been adhered to throughout, and after a little use
will not be found unintelligible. If adopted in the arrangement of a
collection in the cabinet, it would be a good plan to indicate the
recommencement of a fresh branch by a special mark, such as a red bar drawn
above the first (or highest) species."