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be summed up as follows: The first radial branch may intersect with subcosta (Idlaides and Anæa); the cubital cross-vein or its traces occurs in both series (in the Nymphalids in Limnas, Heliconius, Morpho), while traces of the humeral cell of secondaries of the Papilionides are found in the Limnadidæ and Heliconiidæ. It is remarkable that just in these two latter families the resemblance is contradicted by the fact that both display the forked vein viii, in contradistinction to the downwardly curved vein “ix" of the Papilionides. It is this fact that allows me to consider the characters of resemblance as residual and common to the lepidopterous wing, and as undecisive of questions of a nearer relationship. These characters, the traces of the cubital cross-vein, etc., allow of the view that the Limnadidæ and Heliconiidæ retain primitive features and may more nearly represent early stages of the Nymphalids proper. Genera like Dione may supply a connection between the Heliconians and Argynninæ and render the view probable that the brush-footed butterflies are monophyletic.
Variability in the Veining. I have shown (Trans. Ent. Soc. Lond. 1897, 342) that the variations in the neuration within the limits of a species take the same direction with those used to define distinct species or genera. In other words, they follow the chief directions which underlie most changes in the neuration. These latter lie in the breaking up of the median series and the suppression of the radial branches. For instance, in the five-branched forms of the Anthocharini there will be found a tendency to discard one vein in the direction of the four-branched forms of Tetracharis. In a variable species standing between Euchlæ and Tetracharis the disappearing vein may be discarded by anticipation (specialization) or retained by reversion (generalization). In Pontia we have the three-branched form definitely assumed, and we may consider that the ancestry of P. daplidice has passed through the Euchlæ and Tetracharis stages. In the same way the passage of Mancipium to a three-branched form is in process of accomplishment; sufficient material has not yet been examined of brassicæ to determine whether the short apical veinlet is discarded or not in the majority of individuals. In the Zerynthianæ we find individual variation in the direction of the breaking up of the median series; sometimes vein iv, ascends the radius; again, in generalized individuals, it retains its older position
on the cross-vein. It is a mistaken view to consider these variations “abnormal.” They have a definite end and object, and show us how the changes in the venation have been slowly attained. All the species we take cognizance of are seemingly in a certain stage of progression, which temporarily assumes an apparent greater or lesser stability as the insect and its environment are equalized. In Crinopteryx familiella Spuler considers that we have a now variable form in the final stages of discarding the many-branched radius of the secondaries, thus showing us how the wing of Eriocephalus may have passed into that of the aculeate Tineida.
Conclusion. I have taken the present opportunity to review my publications upon the neuration of the diurnals, to compare the figures again with the photographs and preparations. After supplying the missing details in the figures of Parnassius apollo (in which the lower incomplete margin of the humeral cell was omitted) and of Heliconius antiochus (in which the traces of the cubital cross-vein and internal vein were left out), I find nothing to add or alter. The method employed by me prevents errors of commission, but, owing to defects in the preparations, overlooked at the time, it has happened that the above details were not reproduced on the stone.
My studies were entered upon with the view of bringing our classifications into a nearer correspondence with a probable phylogeny. It was unexpected that the result was to confirm the general sequence of Linné and Fabricius, no less than that of the modern authors, Wallace, W. H. Edwards, the Catalogue of Staudinger, at least so far that we may commence with the Papilionides. Since the Parnassians belong beyond question to this stem, and are more specialized than the Swallowtails proper, we should begin with this family. I may reply to comparisons that have been made, that no results obtained in this way, as between ultimate specializations of the same organ in different groups of butterflies, can affect the phylogeny brought out by me. For this latter rests on the primary character offered by vein“ ix," and not upon coincidences in ultimate structure, which are not exclusive, and may well have been independently reproduced upon separate phylogenetic lines. These are characters of convergence, and are not properly used as an index to relationship.
A review of the general neuration shows that the hesperid wing
is the simplest existent form with the veins all separate. A movement in specialization of the radial branches, normal with the lepidoptera, changes this wing into that of the lycænids. Both are now specialized and hardened types, and the position of the median branches has become so fixed that, in their specialization, the middle branch will not yield and submits to extirpation in situ. The condition of the hesperid wing is nearly reproduced in Charaxes, and proves that this was the original condition also of the Pieri-Nymphalid branch. It has been abandoned in specialization through the process of absorption and furcation of the veins; thus the hesperid type of wing becomes the unit underlying all the wing types of the Hesperiades. Into this group, so closed, and having the internal vein (vii) forked at base (viii), we can nowhere properly interpolate a group possessing an additional vein (“ix") and having no fork (viii) to the internal vein (vii), although, as a matter of theory, we may contend that the papilionid wing had also primarily separated veins.
I conceive, then, the Hesperiades to be monophyletic, a development of a single branch or stem of the lepidopterous tree, and as being independent of the Papilionides and their ancestry. compared to the Papilionides, the rest of the butterflies are in the position of the Noctuid branch when compared with the Saturniades. This parallel is not a little exact. The development in evolutionary changes of the Papilionid wing is closely copied by the Saturniadæ, which have but one anal vein on hind wings. We have the same hollowing out of the inner margin in both groups among specialized forms. The Hesperiades resemble generalized moths in having two or more internal veins, and although these are convergent characters, not of phyletic value, they sustain the parallel. The exclusiveness of the Papilionides is supported by vein “ix” of primaries. Wien we take into account their total wing-structure, the idea that we have to do with a radically different development of the lepidopterous type becomes more and more reasonable. I separate, therefore, not the Hesperiadæ, but the Papilionides from the rest of the butterflies, and herein I differ from other authors, no less than from Comstock.
The general inequalities of all the specializations preclude, to a great extent, the question of rank, which practically becomes a matter of more limited importance within the confines of a single group. And I may repeat here, that the specializations of the
larvæ are neither homologous nor dependent upon the specializations of the imago. The external influences by which the different stages are surrounded are radically diverse. It is demonstrable that in Apatela the larvæ are more specialized, as larvæ, than are the moths, as moths. These latter are simple Agrotids, or Hadenids. The larvæ rank with the Arctians in specialization. Generic differences between imagos are not necessarily shown also, but may be displayed independently in the earlier stages of the insect. A specialized chrysalis may be attained by a form which, in the imago state, lags behind its fellows. I ventured first to give this view of the independence in specialization of the stages as early as 1876. Mr. Butler's paper on Apatela remains, at least, an exquisite satire on a generic classification from larval characters alone.
However, I seem to differ from Mr. Scudder (Hist. Sketch, 103), who holds that generic distinctions are as easily traced in the larva as in the imago, thus assuming a parity in specialization. Nevertheless, in the case of the forms of Agrotis Led., we may have moths which offer characters upon which generic distinctions have been founded, while the larvæ are so much alike that no such characters appear with them. And again we find species of Apatela, feebly differentiated in the imago state, proceeding from strongly diverging larvæ. The whole group of Acronyctid genera is held together by specializations of the larva alone. No intimate characters hold Panthea and Apatela united as moths, and here it seems possible that the larval specializations common to both are nonphyletic, convergent, they have been acquired along different routes, and thus the basis of the family Apatelidae would be artificial. Where no such contradiction is offered the development may be assumed as monophyletic, the classification as natural. This view does not militate against the validity of Dyar's general classification as based on the larval tubercles in position. This character, as pointed out by me in '97, is valuable from its indifference to external influences.
In the case of the Papilionides there appears to be the alternative that either vein “ix" has developed subsequently to the disappearance of viii or before its appearance. If we accept the latter, then the Papilionides have branched off, as Prof. Comstock says, long before butterflies assumed their present form (Evolution and Taxonomy, 112). In this case all traces of an immediate ancestry
have, however, vanished. No concession to this fact is made by placing the Papilionides, as Prof. Comstock does, between the Blues and Skippers, clearly, even if distantly, related groups, offering at least no such contradictory characters as do the Swallowtails. Prof. Comstock in his able treatise, to which I am much indebted, does not entertain the view that the Papilionides may not have branched off from the immediate stem of the other butterflies, nor does he apparently insist upon the morphological value of vein “ix.”
The diphylism of the diurnals is founded by me on the following characters : A. Butterflies having a short anal vein on primaries, running from
base to internal margin ; on secondaries only one internal vein ....
PAPILIONIDES. B. Butterflies wanting the anal vein on primaries, instead vein vii
is forked at base (viii), this fork sometimes wanting through degeneration, and having more than one internal vein on secondaries.
All the Hesperiades examined by me have two internal veins to the hind wings, except Pseudopontia, which has three. This peculiar butterfly has the radius strongly specialized, and the retention of the third internal vein may have been necessitated by the circular shape of the wings. Theoretically it may be considered that all the diurnals possessed primitively three internal veins, in addition to the fold (vi), of which the Hesperiades, with the exception above noted, have parted with one, the Papilionides with two veins. In this particular the latter group are more specialized than all the other butterflies. The Saturniadæ, among the higher moths, have reached the same grade of specialization in this particular with the Papilionides. A diminution in the number of internal veins characterizes also certain of the more specialized groups of the Bombycides. The monotypic character of the Papilionides is evinced by the possession of vein “ix" of primaries, in which they appear to differ from all other butterflies, not by the number of internal veins, or by any other characters which they can be shown to share with other lepidoptera. Throughout my writings I have tried to show the direction of the evolution taken by the neuration, and I have accounted for the principal changes in position of the veins by their following these directions in spe