G. C. Crampton.
Evidences of Relationship Indicated by the Venation of the Fore Wings of Certain Insects with Especial eference to the Hemiptera Homoptera.
Psyche 29:23-41, 1922.

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19221 Crmqton-Relationship of Hemiptera-Homopiera 23 /
EVIDENCES OF RELATIONSHIP INDICATED BY THE VENATION OF THE FORE.WINGS OF CERTAIN
INSECTS, WITH ESPECIAL REFERENCE TO
THE HEMIPTERA-HOMOPTERA.
Massachusetts Agricultural College, Amherst, Mass. Ì
In the August issue of Psyche for 1921 (Vol. 28, p.. 116) Mr. F, Muir offers a criticism of certain views proposed by me concerning the origin and relationships of the Hemiptera, and since Mr. Muir's criticism is apparently based upon a complete misunderstanding of my contentions concerning the interrela- tionships of the insectan orders in general, and the Hemiptera and Homoptera in particular, I would take this opportunity of correcting the mistaken impression given by Mr. Muir in his criticism. It is necessary first, however, to clearly understand the interrelationships of the lower forms and allied insects, before taking up the discussion of the phylogenetic development of the Hemiptera and Homoptera, and on this account I would postpone the discussion of Mr. Muir's criticism until the evidence of relationship to be gained from a study of the venation of the fore wings has been presented.
The discussion of the evidences of relationship in the different orders of insects indicated by a study of the venation of the fore wings bas been taken up in the present paper because the wing veins are practically the only structural details preserved in a condition suitable for a comparative study in the fossil pre- cursors of living insects, and because the evidence of the wing venation is apparently the only evidence of relationship which recent students of insect phylogeny deem worthy of their con- sideration! So far as possible, however, I have used the evidence of the wing veins to corroborate the evidences of relationship drawn from the study of numerous other structures of the body as well, thereby obviating the danger of being deceived by con- vergent development-as might be the case if one were to depend upon the evidence of one set of structures, such as the wing veins, alone.
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24 Psyche [~ebruar~
The anatomy of the body in general in the Plecoptera in- dicates that they are among the most important of the living forms which have departed but little from the condition typical, in many respects, of the ancestors of the Orthoptera-like insects, and the higher orders. The venation of the fore wings of recent Plecoptera, however, does not furnish a particularly favorable basis of comparison in attemp$ng to determine the paths of development followed in the evolution of the higher orders of insects, while the venation of the Protorthoptera in par- ticular, and in some respects that of the Protoblattids, (Propalseoptera) Hadentomoids, (Proplatyptera) Megasecoptera etc., as well, apparently furnish certain servicable clews for tracing the origin of some of the developmental (evolutionary) tendencies exhibited in the wing venation of certain of the higher orders of insects.
Since the Protorthoptera appear to be as important as any of the fossil forms suggestive of the precursors of the higher insects, it is of some interest to establish as closely as possible the types ancestral to the Protorthoptera. Handlirsch appar- ently derives the Protorthoptera directly from the Palaeodic- tyoptera (or from the Synarmogoidea, which he derived from the Paleeodictyoptera); but a comparison of the wings of such a Protorthopteron as Spaniodera ambulans, or even the Protorthopteron shown in Fig. 30, with the Protoblat,t,id shown in Fig. 32, would indicate that the Protoblattids -are in- termediate between the Protorthoptera and the Palaeodicty- optera, In the forewings of the lower Protorthoptera and in certain Protoblattids, the anal veins are numerous, and in the hind wings of certain Protorthoptera there occurs an anal fan very suggestive of that found in many Protoblattids. The character of the cubital vein with its numerous oblique branches (cubital bars) and its rather wide extent in the posterior portion of the fore wing, is strikingly similar in both Protorthoptera and Protoblattids, and the nature and extent of the subcostal bars, or veinlets extending from the subcostal vein to the anterior margin of the wing, are much alike in both groups of insects (Protorthoptera and Protoblattids). When the more primitive



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19221 Crampton-Relationship of Hemiptera-Homoptera 25 representatives of the Protorthoptera are compared with certain Protoblattids, it may readily be seen that the branches of the median and radial veins are also much the same in both groups of insects, so that the Protoblattid types of wings may be re- garded as representing as nearly as any known forms, the pre- cursors of the Protorthopterous types of wings; and the Proto- blattids serve to connect the Protorthoptera with the Palseo- dictyoptera. I do not believe that the Protoblattids themselves are to be derived directly from the Palaeodictyoptera, however, but their ancestors were possibly intermediate between the Palseodictyoptera and the ancestors of the Synarmogoids; and the Protorthoptera possibly sprang separately from the same stock, although the Protorthopterous and Protoblattid lines of descent apparently merge as we trace them back to their common stem, so far as the evidence of the wing veins would indicate.
In the reduction of the anals, the shortening of the cubital bars, and the reduction of media to two branches, the fore wing of the Hadentomoid shown in Fig. 10 presents many features suggestive of a rather close relationship with the Protorthoptera, such as the ones shown in Figs. 28 or 26, and the nature of the radius and subcosta is quite similar to that of certain other Protorthoptera. On the whole, however, the type of Hadento- moid wing shown in Fig. 10 might more readily be derived from the type of Protoblattid wing shown in Fig. 12, and it is quite possible that the line of development of the Hadentomoids arose from ancestors anatomically intermediate between the Protoblattids and the Protorthoptera very near the point where these two lines of descent began to diverge from their common Protoblattid-like forebears. The Hadentomoid type of venation is a very important one in suggesting a possible starting point in the the development of the types of venation occuring in the Embiids and their allies, as will be shown later. The character of the anal, subcostal and cubital veins of the Mixotermitoid fore wing shown in Fig. 25, is very suggestive of both Hadentomoids (Fig. 10) and Protorthoptera (Fig. 28)) and the character of the median vein is somewhat suggestive of



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26 Psyche [~ebruar-y
that of certain Protorthoptera (Fig. 9), while the branching of the radial vein is somewhat suggestive of the condition occurring in other Protorthoptera-although the nature of the median and radial veins in the Mixotermitoids is much more suggestive of the Palseodictyoptera. The ancestors of the Mixotermitoids were possibly intermediate between those of the Hadentomoids and those of the Protorthoptera, though the Mixotermitoid type apparently harks back to the Palseodictyoptera in many respects.
In the general character of the anals and the cubital veins, and more strikingly in the nature of the branching of the median vein, the fore wing of the Hapalopteroid insect shown in Fig. 6 ap- proaches the Pr~tortho~teron type (Fig. 9) more closely than any other, so far as I am aware, and the precursors of the Hapalo- teroids are doubtless to be sought among the Protorthoptera or their forebears. I formerly adopted Handlirsch's suggestion that the Hapalopteroids were very like the ancestors of the Plecoptera; but a closer examination of the venation of the Hapalopteroid wings would not bear out this assumption. The more primitive types of forewing venation in the Plecop- tera, such as that of Eusthenia shown in Fig. 13, apparently hark back to a Protoblattid type resembling in some respects the one shown in Fig. 12, in the nature of the cubital and anahins; and the anal fan in the hind wing of Eusthenia is suggestive of the anal fan of the Protoblattid hind wing. On the other hand,. I find much in the venation of the Plecoptera which is suggestive of a rather close relationship to t,he Protorthoptera, and an even closer relationship to the Hadentomoids, particularly in the nature of the branching of media and radius in the fore wing, as may be seen by comparing Fig. 11 with Fig. 10. Furthermore, if we compare the fore wing of the Plecopteron shown in Fig. 11 with the fore wing of the Embiid shown in Fig 8. the branching. of cubitus, media and radius is strikingly similar, and the evidence of the venation is therefore in harmony with that drawn from the study of other structures of the body indicating a close rela- tionship between the Embiids and the Plecoptera-and if the Embiids are to be derived from ancestors resembling the Haden-



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192.21 Crampton-Relationship of Hemiptera-Homoptera 27" tomoids and Protorthoptera in many respects, their near rela- tives, the Plecoptera should also be derived from ancestors resembling the Hadentomoids and Protorthoptera in many respects. It is quite possible that the line of development of the Plecoptera branched off from the common Protoblattid- Pro- torthopteron stem very near the point of origin of the Hadento- moid line of descent, or paralleled these lines very closely and the Plecoptera thus inherited characters found in all three of these groups (Protoblattids, Protorthoptera and Hadentomoids) from the common ancestors which combined all of their common characters in themselves.
As was mentioned above, the Embiid types of fore wings (Fig. 8 and 7) could be readily derived from precursors resem- bling the Hadentomoids (Fig. 10); but the Embiid types like- wise approach very closely to the Protorthopteron types of venation, as one may see by comparing the anal, cubital, and median veins of the Embiid shown in Fig. 8, with these veins in the Protorthoptera shown in Figs. 26 and 28. The se,cond and third branches of radius have begun to coalesce in the Protor- thopteron shown in Fig. 26, thus indicating a tendency toward the further coalescence of these veins which has reached com- pletion in the insect shown in Fig. 8; and in the Protorthopteron shown in Fig. 4, the second and third branches of radius coalesce and the fourth and fifth also unite, as is the case with the Embiid shown in Fig.
7. Furthermore, the tendency for all of the branches of media to coalesce exhibited by the Embiid shown in Fig. 7, also occurs in certain Protorthoptera, such, for example, as the one shown in Fig. 30, in which the media consists of but a single branch. From the foregoing facts, it is evident that the tendencies exhibited by the veins of the Embiids could be traced back to
Protorthopteron predecessors quite readily. On the other hand, the character of the anals, cubitus, media, radius and subcosta of the Embiids shown in Figs. 8 and 7 is strikingly similar to the branching of these veins in the Hadentomoid in- sect shown in Fig. 10, and I am convinced that the ancestors of the Embiids must have resembled both the Hadentomoids and tha Protorthoptera in many respects. The general anatomy of the



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28 Psyche [~ebruar~
Psocids such as Embidopsocus~ for example, suggests a very close relationship between the Psocids and Embiids, and since the Psocids were apparently derived from Protorthoptera-like ancestors (as will be presently discussed) it is to be expected that their near relatives, the Embiids, would also be derived from '
Protorthoptera-like ancestors, so that in indicating an ancestry for the Embiids anatomically intermediate b2tween the Haden- tomoids and Protorthoptera, the evidence of the wing venation is quite in harmony with that from other sources as well. The venation of the Psocid wing shown in Fig. 1 is so similar to that of the Zorapteron shown in Fig. 3) that both were evident- ly derived from the same source, and what applies to one applies to the other as well. The Psocid and Zorapteron wings shown in Figs. 3 and I could readily be derived from the Embiid type of fore wing shown in Fig 7 (as is indicated in the hypothetical intermediate condition shown in Fig. 5)* in the following way. .The second branch of cubitus of Fig. 7 might become more verti- cal, while vein M, which arises from M+Cu and coalesces for a short distance with Rs. in Fig, 7, might unite with Rs further from the base of the wing thus lengthening that portion of M which extends between M+Cu and Rs, as in Fig. 3. R2-t-3 of the radial sector) Rs, bends upward toward Rl in Fig. 7, and if R4+5 were to unite with it to form a single branched Rs bending forward to meet Rl, the condition exhibited by Rs in Fig. 3 would be produced. A deposition of chitin and pigment, in the space between Sc and Rl (as indicated in Fig. 5) would produce a pterostigma such as the one labeled "ps" in Figs. 1 and 3. Judging from $he same developmental tendencies found in the Psocids) Zoraptera, and Embiids, it would appear that all three were derived from a common ancestral source, and many of the genes) determinants) or factors occurring in this common source were inherited by the three derived groups, although they were naturally slightly modified by other factors in the derived groups, as would be expected. As is pointed out in the next paragraph, the ancestors of the Psocids were apparently very similar to the Protorthoptera) and since the Psocids, Zoraptera *The figure in the left hand column between Figs. 3 and 7 is Fig 5, The label was lost from this figure, having been pasted on too insecurely.



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19221 Crampton-Reldiowhip of Hmipkru-Homoptwu 29 and EmbiicIs apparenty sprang from the same source, it is very probable that their common mcestms were very like the Pro- torthopbra in many respects.
That the fore wing of a Psocid could be readily derived from a Probrthopteron protatype may be wen by comparing the fore wing of the Psocid shown in Fig. 2 with that of the Prohr+hop- kron shown in Fig. 4, @me the venation of the two wings is strikingly similax, and the Prokorthopkron type is evidently the more primitive one, since it is one of an older and lower group, and the branching of the veins in generd begins newer the base of the wing-which is usually a more primitive character than for the branches to come off nearer the apex, since the latter usudy indicates a degree of cdescence, and hence a specid- ization, in the veins. The three anal veins are much dike in Figs. 2 and 4, and the forking of the cubitus in the Protor- thopteron shown in Fig. 4 (or b&kr still in the Protmthopteron shorn in Fig. 26) is strikingly Iike that of the Psocid shown in Fig. 2, The three branches of media, and the two branches of & are also strikingly similar in the insects shown in Figs. 4 and 2, and the nature of the first branch of radius and the subcostal vein is much the same in both. The Psocids and Protorthoptera thus apparently have many devdopmmtal tendencie~ in com- moq and prohbly inherited them from a common ancestry which was very like certain Protorthoptera in may respectsy and as was mentioned above, the ancestors of the Zoraptera and Embiids probably also reseinbled the Prohrthoptera in many respects. As will be shown in the next paragrpah, the Psocids and Hemiptma-Hornoptera have so much in common, that they also in all probability were derived from the same type of an- cestors which must likewise have resembled the Prokorthoptem in many respects> although the ancestors of the Hornoptera in dl probabihty resembled the Protoblattids a well, and the '?oob7' of the Hornopteron stem apparentIy strike somewhat more deeply down into the Pal~odictyopterous t.ypes. The peculiar bulging antefrontal region of the head incorrectly called the r'clypeus'' in Cicadid Hornoptera and Fsocids, the peculiar lengthening of the segments of t,he mtem~, whioh, so



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i30 Psyche [~ebruar~
far as I am aware) occurs exactly in that fashion only in the Homoptera and Psocids, the nature of the thoracic terga and ,wing bases) the nature of the tarsal segmentation) and other regions of the leg) the nature of the abdominal segments in .general, the segments of certain males and the ovipositors of certain females in particular) and many other features too numerous to mention at this point) all clearly indicate so close a relationship between the Psocids and Homoptera) that it would be stretching the laws of probability and chance far beyond the breaking point to claim that the marked similarity in all of these structures from a11 parts of the body) and extending through a wide-ranging series of forms) is merey the result of "conver- *gence))' and it would be very interesting to learn from those who continually cry "convergence)) whenever similarities are pointed out between the Psocids and Homoptera) just how ('convergence)) could be brought about in so wide a range of forms and in such a multitude of details from all parts of the body! That the many similarities in structures from other parts of the body extend to the venation of the wings as well, in the Psocids and Homop- tera) is shown in the series of insects figured in Figs. 17 to 24, which includes some of the most primitive) and the most highly special- ized, as well as the intermediate types of venation, in the two groups of insects. Thus, the peculiar ((broken" character of the venation of the apical portion of the Psocid wing shown in Fig. 24 is paralleled by the wing of the Homopberon shown in Fig, 23) al- though the fore wing of the Homopteron Cercopis sp*) figured by Handlirsch) 1909) would have been better for a comparison with the Psocid shown in Fig. 24, than is the case with the Homopteron shown in Fig. 23. The broader more primitively veined Psocid wing shown in Fig. 22 is paralleled by that of the Hornopteron shown in Fig. 21, and the venation in the two is quite similar. Turning next to the intermediate type of venation shown in Fig, 18, it is quite evident that the Psocid shown in Fig. 18 is approached by the Homopteron shown in Fig. 20) especially in the char- acter of the anals) and the branching of cubitus and media) which is strikingly similar in the two groups of insects, and there is evidently a tendency toward the formation of a pterostigma



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19221 Cramp f on-Relationship of Hemiptera-Homopteru 3 1 between the first branch of radius and the anterior margin of the wing) as well as a tendency for Rs to turn forward toward the .anterior margin of the wing. In order to make the series include as wide a range of types as possible) I have included some of the most specialized types as well, and) as one may see by com- paring Figs. 17 and 19) in which radius and media are practically the only veins retained in a well develped condition, there is a marked parallelism in the more highly specialized members of the two groups) as well as in the intermediate and more primitive representatives of the Psocids and Homotera. This parallelism in a wide range of wing types, as well as in a multitude of structures from all parts of the body, can be explained only as the result of the operation of the same developmental ten- dencies (i.e. the expression of the presence of the same genes) determinants or factors-albeit these are modified to some extent in the derived groups by the influence of other factors) inherited from a common ancestry.
From the foregoing facts) I would conclude that the Psccids and Hemiptera-Homoptera were descended from very similar ancestors) and since the Psocids were apparently descended from ancestors closely resembling the Protorthoptera in many res- pects, it naturally follows that the ancestors of the Homoptera must also have resembled the Protorthoptera in many respects, The fact that the saltatorial Orthoptera) which are the modern representatives of the Prot~rthoptera~ have likewise retained many features suggestive of affinities with the Hemiptera- Homoptera is also in harmony with such a derivation of the Homoptera; but there are other factors involved) which further complicate the question of the origin of the Homoptera. The primitive type of venation exhibited by the fore wing of the Homopteron Hotinus sp.) figured by Handlirsch) 1909) appears to be of a lower type than that of most Protorthopterous fore wings) and suggests affinities with the Neuroptera and Proto- blattids, The venation of the Homopteron Ownenis is also very suggestive of that of certain Neuroptera such as Psychopsis, particularly in the peculiar arrangement of certain small cross veins which unite end-to-end to form a paramarginal line extend-



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Psyche
ing parallel to the margin (but at some distance from it) in the fore wing. The nature of the thoracic sclerites of the Homop- tera would lend further weight to the view that the ancestors of the Homoptera were very like those of the Neuroptera) and the fact that many insects descended from the common Neurop- teroid stem) such as the Mecoptera (and even the Siphonaptera) exhibit very similar tendencies in the specialization of their mouth-parts (which tend to lose the ligula) while the labial palpi become approximated and unite to some extent, and the maxil- 1% become much elongate and somewhat stilet-like) would suggest that they and the Homoptera inherited these tendencies from a common ancestry. Furthermore, the fore wings of certain primitive Trichoptera and Mecoptera) which were derived from a common Neuropteroid stem) show undoubted affinities with certain types of Homopterous fore wings, and lend further weight to the supposition that the ancestors of the Homoptera resembled those of the Neuropteroid insects in many respects. Thus, the Trichopterous fore wing shown in Fig. 27 is remarkably like that of the Homopteron shown in Fig. 29) especially in the character of the anal and cubital veins; and the other veins of the wing are also of much the same type in the two wings under con- sideration. A11 of these facts, which indicate that the ancestors of the Homoptera and Neuroptera were very closely related, are in harmony with the fact that the Homoptera and Psocids are also very closely related) since the Psocids themselves are clearly related to the Neuroptera) and their line of development apparently merges with that of the Neuroptera near its point of origin) thereby involving the line of develpoment of the Homoptera with that of the Neuroptera through their mutual relationship to the Psocids, as well as through the more direct affinities of the Homoptera themselves with the Neuropteroid insects. I have therefore maintained that the ancestors of t,he Homoptera were intermediate between those of the Psocids and those of the Neuroptera) and the present study of the fore wing venation would uphold the correctness of this view. If one compares the wing of a Neuropteron such as the one shown in Fig. 34, with the wing of a Protoblattid such as the one



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'3 6 Psyche [~ebruar~
another living insect belonging to a more primitive group; and on this account it is amazing that Mr. Muir should accuse me of deriving living Psyllids from living Psocids especially since I definitely state in a paragraph which he quotes, that the lines of descent of the Homoptera, Thypanoptera, Psocids Hymenoptera and related forms "apparently arose from an- cestors intermediate between the Zoraptera (with the Isoptera) on the one side, and the Coleoptera (with the Dermaptera) on the other." In other words, the ancestors of the Homoptera, Psocida, Hymenoptera, etc., were very similar to the Prot- orthopteron-like and Protoblattid-like ancestors of the Zoraptera and Coleoptera. This is surely a very different matter from claiming that the Homoptera were descended from living Psocids! I have always been careful to state that the Psocids were in many respects verg like the ancestors of the Homoptera, just as the chimpanzees are in many respects verg like the ancestors of man (i.e. the Pithecanthropus-like forms), yet such a statement by no means implies that men were descended from living chimpanzees-and the same principle holds true in the com- parison of the Homoptera with the Psocids, abeit the groups compared in the latter case belong to different orders instead of belonging to different families of the same order, and the differ- ences are naturally somewhat greater in the one instance than in the other. The idea which I intended to convey is that the Psocids and Homoptera are very closely related (i.e. t'hey have both inherited many tendencies in common which cause their lines of development to parallel each other quite closely) and since the Psocids have evidently departed less than the Homop-