fee & 7 = ; c i A NATURAL HISTORY OF THE BRITISH LEPIDOPTERA A TEXT-BOOK FOR STUDENTS AND COLLECTORS BY gmt? [iam Le We POULT, FES. - lt) Author of ‘‘ The British Noctuse and their Varieties,” ‘‘ Monograph of the British Pterophorina,” ‘“‘ British Butterflies,” ‘‘ British Moths,” etc. VOL. I. LONDON: SWAN SONNENSCHEIN & Co., Paternoster Square, E.C. BERLIN : FRIEDLANDER & SOHN, 11, Carlstrasse, N.W. JANUARY, 1899. PREFACH. In submitting this volume to the entomological public, the author trusts that the method of treatment will commend itself. The recent work that has been accomplished in the classification of the Lepidoptera by Chapman, Dyar, Packard and others, has rendered a radical re- arrangement necessary. In commencing with the more generalised, and proceeding to the more specialised, superfamilies, the author con- siders that he has adopted a logical course that will meet with the approval of those best qualified to judge in this matter. It has been considered better to complete thoroughly a few superfamilies rather than to attempt to deal with a large number superficially, and it is hoped that the separate treatment of the main points in the life-history of each species dealt with, will be of advantage to the various classes of entomologists—synonymists, systematists, biologists, and those that study the subject under its geographical, or any one of its philosophical aspects. on large part of a work of this description is necessarily more or less a compilation, and the author wishes here to express his obligation to those authors to whose works he is indebted for information, as well as to the very great number of entomologists (rather more than 200 in number) to whom he is indebted for local lists, and to those who have supplied him with other items of interest that have added to the usefulness and completeness of the volume. These have always been acknowledged, he believes, in the body of the work. There are many, however, who have done much more than this. To Messrs. J. H. Durrant, W. F. Kirby, L. B. Prout and Lord Walsingham, for their help in dealing with matters of ‘‘synonymy,” to Messrs. A. Bacot, W. H. B. Fletcher, Drs. T. A. Chapman and J. H. Wood, for the vast amount of information relating to the ‘‘ life-histories’’ of the insects described, to Mr. G. C. Bignell for notes on the ‘ parasites” affecting them, to Mr. F. Lemann for copious translations from German works, to M. Oberthir for the gift and loan of many rare Anthrocerids, and to Mr. C. Fenn for the generous use of his voluminous note-books, the author tenders his sincerest and grateful thanks. Although essentially a work on British Lepidoptera, it is trusted that it will have an interest for other than purely British lepidopterists. The chapters on each superfamily cover the whole fauna included in the superfamily, and should, therefore, be of use generally to students of these superfamilies. The ‘distribution’ of each species, too, outside the British Isles, is considered separately from the recorded localities within the limits of our own country, and should be useful to students of geographical distribution in all parts of the world. The author is fully aware that in a book containing so much detail, there must necessarily be many sins of commission and omission. He can only hope that these are not serious, and assure his readers that he has taken the greatest care to eliminate them. The trouble to which the author has been put, and the hours of comparatively waste time that he has spent, in compiling the lists of localities, synonymic tables, distribution, etc., and in unearthing records of the rarer varieties and aberrations, owing to the incomplete and imperfect indexes of entomological magazines in general and works on Lepidoptera in particular, have led him to index every reference to super- families, families, genera, species, varieties, etc., mentioned in the book. It is trusted that this will be found of great time-saving value to all who have need to refer to the volume. The publication of a purely technical book of this description would be practically impossible but for the generosity of a section of the entomological public who take an author on trust, as it were, and practically guarantee him against any serious financial loss. 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CLASSIFICATION OF LEPIDOPTERA Part II. THE SPHINGO-MICROPTERYGID STIRPS ... 0566 THE MICROPTERYGIDES ee THE NEPTICULIDES THE COCHLIDIDES (oR 5 BUCLEIDES) THE ANTHROCERIDES INDEX BSE Tne | 102-112 ee hs 129 162 360 383 547-560 Lemann, Frederick C., F.2.s. Llewelyn, Sir John T. D., Bart., m.a., M.P., F.L.S. Lloyd, Alfred, F.c.s., F.E.s. Lloyd, R. Wylie, F.£.s. Lowe, Rev. Frank E., M.A., F.E.8. Lucock, Frank Luff, W. A. Marsden, H. W. ( 6 copies) Mason, Philip B., M.R.c.s., F.L.S., F.E.S. Massey, Herbert T., v.n.s. (2 copies) May, H. H. Maze, W. P. Blackburne-, F.E.s. McIntyre, F. Merrifield, Frederic, F E.s. Moberly, J. C., m.A., F-E.S. (2 copies) Moore, Harry, F.u.S. Morton, Kenneth J., m.A., F.E.S. Moss, Rey. A. M., ma. Mousley, H., F.n.s. Nevinson, Basil G., M.A., F.Z.S., F.E.S. Newland, C. Bingham Nicholson, Charles, F.£.s. Nicholson, William E., F.z.s. Ovenden, Joseph Page, Herbert E., F.n.s. Pearson, (Mrs.) C. N. Peed, John Phillips, Hubert C., u.n.c.s., F.E.S. Pitman, M. A. 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Woolley, H.§., r.z.s, Wright, Dudley, F.R.¢.s., F.B.S. Ashby, Herbert, F.2.s. Nonpareil Entomological Society. Pits ee PIDOP TERA: CHAPTER I. THE ORIGIN OF THE LEPIDOPTERA. For many years entomologists have attempted to work out the line of descent by which the Lepidoptera have been evolved. Mclachlan, in 1865, and Speyer, in 1870, pointed out certain broad affinities between the Trichoptera (caddis-flies) and some families of the Lepi- doptera. Packard, in 1863, had also suggested a relationship between the two orders. ‘The co-ordinal value. of the two orders, however, was maintained by all these writers, and it was not until 1896 that Sharp, commenting on the pupa of a species of Micropteryx (probably semipurpurella), stated that he ‘‘ considered the pupa to be that of a _Trichopterous insect,” and that Micropterya should be referred to that order, and that, if this course were not adopted, he felt clear that Trichoptera could not be maintained distinct as an order from Lepi- doptera. Chapman had previously described* at length the pupal jaws of Micropterya, and pointed out that they exhibited characters quite unique among the Lepidoptera. There is, however, a group of Lepidoptera, in some respects, pro- bably, more generalised than the Microrrerycipes. These are the ERriocePHALIDES—comprising the British species, calthella, seppella, aruncella, thunbergella and mansuetella. Walter} discovered that the imagines of HK. calthella had maxille constructed on the type of those of biting or mandibulate insects. Chapman has describedt the way in which the jaws are used in eating the pollen. The generalised mouth-parts of Hiiocephala consist of maxillary lobes, mandibles, etc., but not only do they differ from all other Lepidoptera in this par- ticular, but the thorax and abdomen of the imago are also more generalised. Both the Micropreryeres and the HriocerHatipes have the fore- and hind-wings united by a jugum, and, in this respect, as well as in the highly generalised condition of the neuration, they resemble the Trichoptera. Another super-family with Trichopterygid affinities is the Hmpra- LIDES. Speyer, in a very interesting paper§, refers to the similarity of * Trans. Hnt. Soc. London, 1893, p. 263. | Jenaische Zeitschrift, 1885. t Trans. Ent. Soc. London, 1894, p. 338. § Stett. Hnt. Zeitwng, 1870, 9, BRITISH LEPIDOPTERA. the neuration of the Hepialidae and Cossidae, and remarks that they resemble the Trichoptera no less than the Micropterygidac, though the Hepialidae exhibit other close analogies with the Trichoptera. He also adds that the middle cell of the wing in the Phryganeidae is not fundamentally different from that of the Heptalidae, Cossidae and Micropteryyidae, whilst the hind-wings of the Psychidae exhibit similar characters. This brief summary indicates the directions in which it has been suggested that the Lepidoptera are allied to the Trichoptera. The nature of the alliance has been variously discussed, but the general conclusions reached fall into one of two lines :—(1) That the Lepi- doptera have descended by way of the Micropreryeipes, Hrpranimes, and Psycurpes directly from the Trichoptera. (2) That the Trich- optera and Lepidoptera have developed from a common ancestor. To discuss this matter satisfactorily we must first consider the similarities between Lepidoptera and Trichoptera. The resemblance between their larve is very strong, their external structure being almost the same, the principal difference being that the lepidopterous larva possessesabdominal prolegs. These, however, are absent in Micropterygid larvee, as well as in other lepidopterous larvee whose habit itis to mine into their food-plants. The similarity of the pupa of Micropteryx to that of the Trichoptera has been already noticed. The abdominal seements of both are more or less freely movable upon each other. They form the ‘‘ Pupz Liberee”’ of Packard, whilst those generalised lepidopterous pup, which have a considerable number of free (movable) abdominal segments, the ‘‘ Pupe Incompletz”’ of Chapman, are much nearer to the ancestral forms than the ‘‘ Pups Obtectz,”’ which represent the more specialised forms. The lepidopterous pupa has been looked upon as presenting a sub- imaginal condition of a type midway between the ametabolous and metabolous orders of insects. This has been suggested by the con- dition of the pupal wing-cases, which are similar to those of metabolous nymphs, such as Dermaptera, Vermitidae, Psocidae and Hemiptera. Spuler has shown that the neuration of the lepidopterous pupa is almost identical with that of the Blattidae and Fulgoridae. Packard says that the ‘‘ wings of the lepidopterous pupa may be said to be in the nymph stage of the ametabolous insects mentioned, since they are direct outgrowths from the tergites of the segments from which they arise.” He further says that ‘‘if the wing-cases of any lepidopterous pupa, together with the meso- and meta-thorax are, before the larval skin is moulted, removed and spread out,’’ it will be seen that ‘‘ they bear, as Spuler shows, a striking resemblance to those of a beetle, Vvrmes, Psocus, or any hemipterous insect.’’ He further points out that the pupal neuration, as well as the appendages—mazxille, labium and lees—are ancestral and phylogenetic, showing considerable differences when compared with the corresponding structures in the more specialised imago. The importance of the pupa, as bearing on the origin of the Lepi- doptera, is also very evident when the more generalised forms of the lepidopterous pupa are compared with the more generalised forms of the dipterous pupa, as exhibited by the Dibionidae, Tipulidae, etc. Packard asserts that the close resemblance between the orthorhaphous dipterous pupa and Tineid pupa, affords strong evidence that the two ORIGIN OF LEPIDOPTERA. 3 orders are not only very closely allied, but even that they may have originated from a common ancestry, the loss of thoracic, and of abdominal, limbs, and the reduction of the head and its appendages in dipterous larve, as well as the reduction of the hind-wings, being due to modification from disuse. In the dipterous pupa, as exemplified by Culev, the hind pair of wings is nearly as well-developed as are those of lepidopterous pupe. There appear to be many Neuropteroid characters in the imagines of the more generalised Lepidoptera, and these have been, of course, those from which the phylogeny of the order has been principally studied. ‘There are the square head, the small eyes, the vestigial mandibles; the retention of the maxillary palpi, and of the lacinia and galea (or rather the homologues of these in the form of the maxillary lobes) in the Eriocepuanipes ; the large meta-thorax with separate scuta, the exserted large male genital armature of the Micropreryeies and the Psycuipss; the Trichopterigiform neuration of Hepialids and Hiriocephalids, etc. As we pass from the more genera- lised to the more specialised forms of Lepidoptera, these characters become exceedingly modified, and are often entirely lost. We have before pointed out that Speyer was one of the first to show the resemblance of the Hepialid, Cossid, Micropterygid and Psychid neuration to that of the Trichoptera. He also pointed out the fact that there were certain Lepidoptera—Heteroyenea, Adela, Micropteryx — whose pupz possessed free limbs, and also that certain species of both orders spin a cocoon. Speyer, however, was inclined not to consider the Lepidoptera as descending directly from the Trichoptera, but that both had a common origin, the latter being the first to appear, and that the common ancestor probably had an aquatic larva. He further noticed that their mouth-parts were, in reality, very similar. The close relationship between the Trichoptera and Lepidoptera was also shown by Muller, who claimed that there was the closest affinity between the Phryganeidae and the Lepidoptera, and that both had proceeded from a common stock. Packard, however, shows* that there is considerable difference between the mouth-parts of the two orders, and concludes that, with respect to the structure of the maxille, the Lepidoptera are nearer the ametabolous mandibulate insects than the Trichoptera. The same author also compares the neuration of the Er1ockEPHALIDES and the Micropreryerpes with that of Amphientomum, a generalised Psocid, and he considers it ‘‘ not impossible that these insects, with their reduced pro-thorax and concentrated or fused meso- and meta- - thorax, together with their maxillary fork, may have had some extinct allies, which were related to the remote ametabolous ancestors of the Lepidoptera.”’ Hermann Miller has also suggested a close relationship between the Tipulariae, the Lepidoptera, and the Phryganeidae, and compares the similar neuration of Limbnobia and Ctenophora with that of the Phryganeids, and states that ‘‘it is far easier to deduce morphologi- cally the proboscis of the Tipulae from the buccal organs of the Phryganeidae than from those of any other order of insects.” Chapman's studies of the pupa have led him to make some im- — * Bombycine Moths of America, 1895, p. 55. 4 BRITISH LEPIDOPTERA. portant statements* on the probable origin of the Lepidoptera. He considers that the history of the evolution of the lepidopterous pupa has been largely an attempt to solve the question as to how to escape from the pupa without the aid of imaginal jaws. Without going into the question of how the quiescent pupa of bees or beetles was derived from the active larva-like pupa (if the term, indeed, is at all applicable), such as those of bugs and crickets, he shows that ‘ the great mass of Coleoptera and Hymenoptera have a pupa of very uniform type, help- less from its quiescence, and hence resorting for protection to some cocoon or other cavity ;’’ these pupe haye (as a rule) a very delicate cutaneous structure, and possess no hard chitinous parts. There are many exceptions in these two orders in which the pupa is exposed, and consequently of harder external texture. So far, then, there is considerable similarity in the needs of many of the pupe of Lepidoptera, Coleoptera and Hymenoptera, and the necessity of special modification to allow the imagines in all to escape from the cocoon is evident. In the Hymenoptera and Coleop- tera this is effected by the imaginal jaws, for the imago becomes per- fect within the cocoon, and it not only throws off the pupal skin within the cocoon, but remains there till its appendages have become fully expanded, and more or less completely hardened. In some instances—the Cynipidae—the jaws are required for no other purpose. Chapman states that one or two of the Neuropterid families appear, in this particular, to have followed out precisely the same lines as the Coleoptera and Hymenoptera, whilst others, having developed a quies- cent pupa of delicate structure, have retained well-developed mandibles, by means of which the pupa escapes from the cocoon immediately previous to the emergence of the imago. This peculiar structure - associates, of course, the Neuropterous insects possessing it, the Phryganeidae, and the Microrreryemrs. Although the connection between the two latter is evident, yet Chapman points out that there are objections to Sharp’s proposal to class the Micropterygids with the Phryganeids, the most important of which is, that the former have lost the imaginal jaws, and possess a distinctly lepidopterous haus- tellum. The phytophagous habit, too, although strong in the Phryganeids, is absolute in the Micropterygids, so that the affinities of the latter are rather with the Lepidoptera than the Trichoptera. The Coleoptera and Hymenoptera, however, as a rule, require imaginal jaws for the purpose of obtaining food. ‘This is not so in the Lepidoptera, nor in the other highly specialised order, the Diptera. Having no special use for imaginal jaws, these orders have not retained them simply to escape from the cocoon, but have met the- difficulty of escape from the cocoon, without the aid of imaginal jaws, by various modifications. Up to a point their solutions were very similar, although in the most specialised Diptera one or two remark- able advances haye been made, of which there is no trace in the Lepidoptera. Taken as a whole, then, there is much similarity between the lepidopterous and dipterous pups. Chapman states that he sees every reason to believe that the Diptera also originated from a Neuropterous base with the Lepidoptera. As throwing further light on the affinities which exist between the Lepidoptera and Trichoptera, Kellogg records that the mode of tying * Trans, Ent. Soc. Lond., 1896, pp. 567-569. a ORIGIN OF LEPIDOPTERA. 5 the fore- and hind-wings together by a jugum, such as exists in the Hepialids and Micropterygids, is the same as obtains in many of the Trichoptera. He further found, in a study of the scales of the Lepi- doptera,* that, in addition to the ordinary specialised lepidopterous scales, there was, on the wings of the Micropreryeiprs and Hepratmss, a covering of very fine hairs, differing radically from the scales in size, arrangement, and mode of attachment to the membrane, and he con- siders that these hairs are practically identical with the clothing of the wings of the Trichoptera, only that they are in a more generalised state. On the other hand, he finds on the wings of the Trichoptera, in addition to the fixed unstriated hairs, a sparse covering of specialised hairs, striated, set in sockets, and easily rubbed off, which he looks upon as the lepidopterous scale in a generalised state. He concludes that the stem-form of the Lepidoptera possessed a wing-clothing very much like that now exhibited by the Trichoptera. In another paper}, Kellogg shows that the mouth-parts of the Trich- optera bear considerable affinity with those of Lepidoptera. He says that ‘the maxille and labium in general characters are similar in the two groups,” whilst ‘‘ the matter of the mandibles is of special interest. In certain species of Micropteryx (i.c., in the Hriocephalids) they are present as functional organs, although the tendency towards their reduction is fully displayed within the limits of the genus. In Trichoptera, functional mandibles have not yet been found, although the distinct rudiments of mandibles are present. Manifestly now, as the tendency of specialisation in both groups is towards a reduction to complete atrophy of the mandibles, the Juaarm cannot be looked upon as in any way lineal descendants of the Trichoptera. ‘The affinity of the two groups must be of the character of two dichoto- mously divided lines of descent, diverging from a racial type, which possessed conditions of mouth-parts, wing-neuration, wing-clothing and thoracic structure, of a character suggested by the present con- ditions of the organs presented by the generalised members of the two groups.” Still another papert by this author throws considerable light on the subject under discussion. By the comparison of the lepidopterous neuration, as exhibited in Micropteryx and Hepialus, with that of the Trichoptera as exhibited by Newronia, as also with that of Panorpa, he shows that the similarity of the neuration is very considerable, and states that, on the fore-wings of all, ‘‘ the simple unbranched subcostal (nervure), the five-branched radius, the persisting stem of media coalescing at its base with cubitus, the three branches of media, and the reduced anal field, are common characters. In the hind-wings, the general character of the neurational uniformity is only varied by differences which, in themselves, are additional evidences of a com- munity of plan.’ It is impossible here to discuss this particular phase any further, and we can only state the author’s conclusion, that the Trichopterous and Lepidopterous wings ‘“‘may have had a generalised prototype very like the Mecopterous wing.” Meyrick also refers to the close similarity existing between the * The Taxonomic value of the scales in the Lepidoptera, pp. 45-89. + ‘‘ The mouth-parts of Lepidoptera,” American Naturalist, 1895, p. 546 et seq. {The affinities of the lepidopterous wing,” American Naturalist, 1896, p. 709 et seq. 6 BRITISH LEPIDOPTERA. neuration of Palaeomicra, a New Zealand genus of the ErtocePHALIDES, and that of Rhyacophila,a genus of Trichoptera. The only important difference is, that in Rhyacophila there 1s an additional nervure arising out of 4 (lower median, Meyr.) in the fore-wings, although it 1s interest- ing to observe that this very nervure has disappeared in the hind-wings. Nothing at all approaching this form of neuration is known in any other order of insects, and Meyrick considers that it is highly impro- bable that so complex a type could have originated twice independently. It may be observed from the above summary of the latest facts at our disposal on this subject, that the opinion is pretty generally held that the Lepidoptera and Trichoptera originated from a common neurop- terous stock. It is not probable that either originated directly from the other, but it is very possible that they branched quite indepen- dently, and so represent two distinct lines of descent, originating from a common ancestral base. ‘There is also considerable probability that the Diptera originated from the same source, as this order shows considerable affinity with the Lepidoptera. CHAPTER Il. THE OVUM OR EGG. Ir would appear that there is a tendency for the eggs of all organised beings to assume a more or less ovoid or spherical form. Among the eges of Lepidoptera this general tendency is well maintained, and we find them roughly divisible into two forms: (1) Ovoid, longer than high, with the long axis horizontal, a shorter axis vertical. (2) Up- right, more or less spherical, with the horizontal axes practically equal, the vertical axis equal, longer, or shorter than the horizontal. The primeval lepidopterous egg was probably ovoid, colourless and transparent, with no sculpturing on its cell wall. This form of egg is practically that which is laid by the Micropterygids, Adelids, and other Lepidoptera that cut out a pocket in a leaf and deposit their eggs in the soft cellular tissue of the leaf. This form of egg would, if laid in an exposed situation, soon undergo modifications in many directions, arising from the need of protection and concealment, and it is possible that, under these conditions, one may find isolated examples of almost any form in any of the families, although the simplest form of egg must generally be found in the lower families, and no highly-developed structure can occur, except among the species of those families that have undergone a large amount of specialisation and elaboration. The egg of a lepidopterous insect consists of an outside shell, en- closing protoplasm, which is, at first, homogeneous. The shell, which forms a thin pellicle, is usually divisible into a base, walls, and apex. At that pole of the egg, usually termed the apex, there is, as a rule, a microscopic depression, from the base of which minute canals lead into the egg, and carry the spermatozoa for the purpose of fertilisation. This is called the micropyle. It will be at once observed that this definition, so far as relates to the micro- ff THE OVUM OR EGG. pyle being placed at the apex of the egg, is quite conventional, for, although the micropyle is actually at the apex in spherical, or, as they are usually termed, ‘‘ upright,”’ eggs; on the other hand, it is at one extremity of the long (horizontal) axis in ovoid, or, as they are usually termed, ‘flat,’ eggs. Since the ‘ upright” egg has more probably been evolved from the ‘‘ flat’? form, than vice versd, it follows that, when we use the term ‘‘ base”’ in the two forms of egg for that side by which the egg is usually attached to the surface of the food-plant, or other object on which it may be deposited, by the parent, the sides are not homologous in the two structures. In general, we speak of the side opposite the micropyle as the base. It follows, therefore, that we speak of a Noctuid egg as being laid on its base, and, to get rid of the anomaly, we speak cf a Geometrid or Lasio- campid egg as being laid on its long side, whereas, as we have already suggested, the older form of egg is probably that which is laid on its long side, which should then, in reality, be called the base. The greater number, by far, of the families which used to be included under the title of Micro-Lepidoptera have ‘ flat’ eggs; such are the Micropterygids, Tineids, Pterophorids, Gracillariids, Gele- chiids, Pyralids, etc. With this group the higher Geometrids and Brephids, which also have flat eggs, may be considered. Another important group with flat eggs, consists of the Zygenids, Lasiocam- pids, Saturniids and Sphingids. The Lepidoptera with upright eggs are the Cossids, Cymbids (Chloéphorids), Notodonts, Noctuids, Liparids, Arctiids, Hesperids and Papilionids. ‘There are, undoubtedly, a few of the so-called Micro-Lepidoptera with upright eggs, e.g., Chrysocorys festaliella, but very little is known of the eges of these moths. The base of a lepidopterous egg, then, as hitherto used by ento- mological authors, is a doubtful quantity. It has been considered by some as that side by which it is attached to its food-plant; it has been considered by others as that side opposite the micropyle. We use it in the latter sense, as tending to preserve correctly the homologies of the egg structures. The side by which an egg is attached to any object is usually flat and devoid of characteristic markings, but the walls are generally sculptured in some form or other, although they are, in a few cases, quite smooth. The flat eggs are, as a rule, ornamented only with rough pittings, worked up in some cases into a roughly polygonal reticulation ; they rarely have longitudinal ribs, although certain Geometrids—Gnophids and Acidaliids—exhibit this style of orna- mentation. The eggs of Geometrids offer many remarkable modifica- tions in their sculpture, from the almost smooth egg of Tephrosia, to the marvellous polygonal reticulation (with a white knob at each angular point) presented by Hurranthis plumistraria and Hemerophila abruptaria. The Zygenid egg is characterised by its bright yellow colour, with one pole quite transparent; the Lasiocampid egg by its tiny raised points at the angulations of the finest conceivable reticula- tion, and by its opalescent markings. The Sphingid egg is almost devoid of markings, the micropyle often being practically indistinguishable. In the upright eggs, however, the ornamentation becomes much more complex. The pitting takes the form, generally, of hexagonal cells, and longitudinal ribs stand out from the surface of the egs, and run from the base to the apex of the egg, the ribs being generally lost 8 BRITISH LEPIDOPTERA. on the edge or rim of the micropylar depression. In the Noctuids this hexagonal cell structure, which is separated by the longitudinal ribs, is entirely lost, and there is a series of transverse ribs running parallel to the base, dividing the depressions between the longitudinal ribs into a series of ladder-like spaces. This is also a common form of sculpture in the Pierid and Nymphalid eggs. The micropyle is usually placed at the base of a slight depression situ- ated at the summit of an upright egg (‘.c., at the extremity of its vertical axis), and at one of the ends of the long (horizontal) axis of a flat egg. It consists of a number of delicate microscopic canals, which vary in number, but there are rarely less than four or more than six. ‘They radiate from a minute depression, surrounded by a rosette or circle of cells of the greatest delicacy. In some eggs, even when viewed under a powerful lens, no alteration in the ordinary outline of the egg is caused by the micropylar depression; in others, however, where it is more depressed it is readily distinguished. In some eggs, again, there is a considerable micropylar basin, the micropyle proper being situated at the base of this. The upright egg, as we have seen, exhibits what is probably the most specialised type, and we find the eggs of some Noctuids and Papilionids very highly specialised. The Noctuid egg is usually of a hemispherical shape, somewhat flattened at the base, but those of the Xanthids have raised ribs rising above the central point, or apex, and curving down thereto; they are, therefore, not unlike, in a general way, the egg of a Vanessid. The egg of Phytometra viridaria (aenea) is cut up by two sets of oblique lines into diamond shaped spaces, at each point of which there is a large red-brown spine, standing perpen- dicularly to the surface of the egg. But the eggs of certain Papilionids are, probably, the most specialised. Among these, the Vanessid egg is of a barrel-shape, with eight or ten highly developed longitudinal ribs. The nine-pin shaped eggs of the Pierids may have as many as thirty or forty longitudinal ribs, whilst the tiarate eggs of the Liycenids have a most complicated ornamentation, owing to the prominence of the longitudinal ribs, and the depth of the transverse pitting. The egg of Polyommatus corydon, with its dahlia-like appear- ance, must be seen under a microscope to be appreciated, whilst those of P. icarus and Plebeius aegon are equally complicated and beautiful. The egg of Thecla w-album has a series of layers of prominent white pointed cells forming a saucer-like base, which holds a flat, truncated cone of a dark reddish colour, with a conspicuous, circular, micropylar basin at the summit. The egg of Limenitis sibylla is covered with fine transparent hairs, resembling spun glass. In cross-section, too, the Lycenid egg gives a polyhedral or hexahedral appearance, and not the more or less circular one common to butterflies. There are other peculiarities that may now be briefly noticed. The typical Geometrid egg is usually oval or ovoid in form, with a de- pression on the upper face, but in H’nnomos, it assumes the appearance of a rather square-based parallelopiped, and a somewhat similar shape is seen in the egg of Crocallis elinguaria. Brephos and Thyatira, which have been placed by various systematists among the Noctuids, have eges of Geometrid appearance. The eggs of Tortricids and Cochlio- podids have the appearance of flat scales, and so have those of many Pyralids. THE OVUM OR EGG. 9 We have seen that certain families are characterised by their species possessing a flat egg, za that others are characterised by their Species possessing an upright eg The Lasiocampids have a flat egg, yet the eggs of Hriogaster ie and Clisiocampa neustria and C. castrensis have the appearance of upright eges, so far as their position with regard to the twig on which they are laid is concerned. This, however, is not really so, for the eggs are laid upon their long sides, on each other. A case of precisely opposite character occurs among the Noctuids, the eggs of Leucania littoralis being laid on their sides upon (or against) each other, although theoretically, no doubt, they may be assumed to be laid uprightly upon the edge of the fold of the leaf, in which they are placed. There is considerable difference in the thickness of the eggshell of various lepidopterous eggs. In many species, it is so thin that the development of the embryo can be distinctly traced through it. The egos of Tortricids and Pyralids are specially remarkable for the thinness of their shells; but, even in the same super-family, there is consider- able difference. Among the Papilionids, the shells of Vanessa io, of Pararge and of Nemeobius, are very delicate; those of the Lycenids and Pamphilids are particularly tough and opaque. The egeshells of Leucania littoralis among the Noctuids, of Callimorpha hera and Huthemonia russula among the Arctiids, of all the species of the Zygenids, are all exceedingly delicate. When the egg is first laid, the outer pellicle is soft and yielding, and, if it be disturbed ever so slightly, an impression is made in its external appearance. In some cases, the egg, when first laid, is ex- ceedingly soft, and looks asif it were ‘almost fluid. Such eggs, laid on glass, apply themselves to it, and have a very regular and almost perfectly circular or oval outline ; but if laid on a leaf or other irregular surface, they apply themselves to its irregularities, and become them- selves irregular, both in relation to the surface to which they are applied, and also as regards their disturbed outlines. Chapman refers to the evident irregularity observable in eggs laid by Scopula decrepi- talis on a Teucriwn leaf. The base of the eggs of Colias sometimes spread considerably ; the eggs of Gonepterya ‘rhamni are often flatter on one side than the other. EKgegs of Pieris and Huchloé also show a basal flattening that would probably not occur if they were quite free. The ege of Calligenia miniata, which has a very Pierid appearance, varies much in shape, some eges being much stumpier than others. The variation in the shape of the eggs of Tephrosia bistortata and T. crepuscularia (biundularia), even when laid quite free, is considerable ; whilst the eggs of these species, as well as those of Anchocelis litura, A. pistacina, Orrhodia vacciniit, O. ligula, Dicycla oo, and others, pushed into crannies of bark, may sometimes become so altered by the process, that the typical shape and ribbing are entirely lost. This is the case also with the eggs of Leucania littoralis, which are laid, as before noticed, in the folded edge of a leaf. In eggs of this descrip- tion, it need hardly be said, the change in shape eas, no injurious effect on the development of the embryo. There is, sometimes, considerable difference in ny size of eggs, even when laid by the same moth. Harwood has noticed differences in the size of the eges among the Notodonts, and is inclined to associate the difference in size with a difference in sex, assuming that 10 BRITISH LEPIDOPTERA. the larger eges produce females, the smaller, males. Hellins observes that of about twenty-three eggs laid by a female Smerinthus populi, the last laid eggs were only two-thirds of the size of those first laid. Chapman has recorded that there is considerable. variation in the size of eggs laid by the various species of Acronyctid moths. In Triaena tridens there are, apparently, at least two races which lay differently sized and differently ribbed eggs, whilst the eggs of Pharetra euphorbiae var. myricae also vary very much in size. The eggs of Lepidoptera do not vary much in colour when first laid. They are usually whitish, pale yellow, or pale greenish in tint, but, after they are laid, they change colour very quickly, and the colour then probably becomes of that hue which will most exactly harmonise with the surroundings among which the egg is usually laid. The eggs of Thecla w-albun are laid above, or directly below, an aborted leaf-bud, and harmonise so exactly with the colour of the bark of the elm-twig on which they are placed, that only an entomolo- geist could possibly detect them. They appear to be placed always on the old, and not on the growing twigs, and thus everything tends to aid in their protection. . The first colour-change of the lepidopterous egg usually takes place within a few hours (12-72) of an egg being laid. After this first colour-change, many eggs undergo a whole series of complicated colour- changes, due to the development of the embryo within, the changes being easily followed through the transparent egg-shell. Robson says that the change of colour of the newly-laid Hepialid egg, from white to black, isa change in the colour of the shell only, and this is so, for the egg-shell remains black after the young larva has left the egg. Many eggs, however, like those of the Hepialids, change colour but once (directly after being laid). The egg of Huchloé cardamines is yellow when laid, becomes deep orange in about twenty-four hours, and, with the excep- tion of a slight change just before hatching, remains of this tint. The egg of Endromis versicolor is pale green when laid, rapidly becomes yellow, then changes to orange, and finally to purple. Jordan records an opaque white ege of Cerura vinula, instead of the usual chocolate- ” coloured egg. Hellins observes that eggs of the same species vary in colour, and do not always go through the same changes of colour when approaching maturity. He instances Oryyia antiqua, Cerura vinula, Hepialus sylvinus, and Chetimatobia brumata. The changes which Chapman has chronicled* as taking place in the Acronyctid eggs while maturing, are exceedingly interesting. These changes may vary according to temperature, the colouring of Pharetra runiicis, which is assumed in two days in warm weather, taking a week in cool weather. The egg of Leucania littoralis is at first pale yellow, then it becomes orange, then mottled with reddish, and at last slightly purplish, at which stage the shell itself is seen to be perfectly trans- parent, and the embryo may be observed within the egg-shell. The ege of Acontia luctuosa is pale yellow, then whitish with a row of red- brown spots just above its equator. The egg of Phytometra viridaria is pearly white, then it develops two bright claret-coloured rings, one of which surrounds the micropylar area and the other the shoulder of the egg; after this the red areas become enlarged, and tend to join. Many eggs exhibit a similar wide series of colour-changes during the development of the embryo. * Entom. Record, etc., v., pp. 140-146. THE OVUM OR EGG. il It will be at once manifest, if an ege be kept under observation under the microscope, that most of the colour-changes taking place within the egg are very closely connected with the developmental pro- eress made by the embryo. The first change, which occurs very soon after the egg is laid, probably represents the transition of the egg- contents from their primal homogeneous condition, to that which is reached when the blastoderm layer is developed, and which is accom- panied by the separation of the contents from the egg-wall. There is, at this stage, sometimes, a distinct change of tint, at others, the whole surface becomes completely covered with black dots. The second change appears to take place with the formation of the germinal band, and appears to be intensified as the growth of the embryo continues. ‘This probably accounts for the general darkness of the colour assumed at this stage ; dark brown, red, purple and leaden are tints frequently met with, and these sometimes last for a con- siderable length of time. The third change of colour usually exhibits an intensified foc of that occurring in the previous stage, except that the apex, and fre- quently the base of some eggs, becomes pale again. Sometimes, at this stage, the egg-shell is quite transparent, and the movements of the embryo are readily observable. This is particularly the case in many eggs just previous to the escape of the larva. Eggs also vary in their ornamentation. We have already suggested that the primitive lepidopterous egg was smooth, and, at the present time, with the exception of minute pitting and faint polygonal reticu- lation, the majority of flat eggs are comparatively smooth. The Geo- metrid ege appears to be more generally highly ornamented than that of any other flat-egged family, except, perhaps, those of the Crambids. There is, however, a very considerable amount of variation in the detail of the ornamentation, even in this group, e.., the ege of Hemerophila abruptaria is covered with a network of hexagonal “cells, with a glistening white knob or button at each angular point, but here and there heptagonal and pentagonal cells exist side by side, where one of the knobs has migrated to an adjacent cell; this is a common form of variation in this type of ornamentation. In the groups with longi- tudinal ribs*the number of these often varies; thus, in the ege of Catocala fraaini the number varies from 22-27, in Polygonia egea there may be 9 or 10, in Leucophasia sinapis 11 or 12. Chapman says that, as a rule, the egg of Hwyonia polychloros has eight ribs, but that sometimes there are only seven, also that Polyyonia c-album may have ten or eleven ribs, and Edwards gives the same numbers for the allied P. interrogationis. Chapman finds that in Pharetra (Acronycta) auricoma the number of ribs varies from 57 to 60,in P. albovenosa from 41 to 45, in Tviaena tridens the average number is 38, but that sometimes there are as many as 44, whilst one batch of eges of this species had from 49 to 52 ribs. In T. pst the number is rarely fewer than 45, and some specimens have as many as 54; in Acronicta leporina the number varies from 41 to 68, whilst in Apatela aceris the number may extend from 50 to 75. It appears to be, indeed, a very general form of variation in almost all eges with a moderate number of longitudinal ribs. The variability in the number of ribs is almost equalled by that of their arrangement. The egg of Cirrhoedia werampelina has 24 or 25 longitudinal ribs. Normally, these ribs should be alternately long 12 BRITISH LEPIDOPTERA. and short, the former running from the base to the summit, the latter stopping short at about one-fourth the distance from the top. Really the arrangement is rather irregular; in one egg examined there were two short ribs between two successive long ones, whilst in another case the short one was missing. In the egg of Tiliacea (Xanthia) aurago there are 15 ribs running from base to apex, each alternate one failing before reaching the summit; but there is considerable variation in their arrangement,.one, two, and even three of the shorter ones being sometimes obsolete in one egg. Theoretically, the 27 longitudinal ribs of Dasycampa rubiginea should be alternately long and short, but frequently two short ones are adjacent, more rarely two long ones. The manner in which the longitudinal ribs unite just before reaching the micropylar area is also very variable.. The number of eggs laid by various species differs greatly, and, among different individuals of the same species, there 1s considerable variation. Hellins records 1,200 as the number laid by a female T'i- phaena fimbria; Riding gives 700-800 as the number laid by 7. pronuba; Hollis says that Spilosoma lubricipeda lays from 400 to 500; Nicholson gives above a thousand as the number laid by three Peridroma saucia; Zeuzera pyrina is reported to lay between 1,000 and 1,100; a female Dasychira pudibunda laid 274 eges ; whilst Hpunda lichenea is accredited with laying above 200. There is no doubt that the average number laid by many species is a very high one. The eggs are laid in a variety of ways and positions. The Hepialids drop their ova among the herbage loosely, the tiny eggs quickly finding their way to the roots of the plants on which the larvee feed. Lasiocampa quercis does the same, and so does one of the most highly specialised of our British butterflies, Melanargia galatea. A large number of moths lay their eggs solitarily on, or near, the food-plant of the larvee, whilst others lay them side by side in clusters. The Zygenids often heap their eggs in two or three layers. Clisio- campa (Malacosoma) neustria, C. castrensis, Eriogaster lanestris, and Anisopteryx aescularia lay their eggs in rings around the twigs of their respective food-plants, forming a kind of necklace around the stem. The Amphidasyds (A. betularia and A. strataria), and the Tephrosiids (7’.. bistortata and T. crepuscularia), like Aeuzera pyrina, are provided with long ovipositors, to enable them to lay their eggs deep in the crevices of the bark of the trees on which their larve feed. The egg of Z’rochilian bembeciforme is laid on the underside of the leaf of an osier, although the larva is a borer, and feeds on the solid wood. The female Leucania littoralis folds over the edge of a grass leaf, and lays her eggs in a string within the fold. The Geometrid moth, Jodis vernaria, lays its eggs one upon the other in rouleaux, seven or eight in each row, and resembling a slender twig or tendril of Clematis, on which plant the eggs are laid. Polygonia c-album and P. interrogationis have a precisely similar habit. The eges of the Pyralids usually partially overlap, and the same imbricate arrangement is found in certain Geometrids, e.g., Hinomos quercinaria, and certain Noctuids, e¢.g., Mellinia circellaris (ferruginea), the Acronyctid tribe, Viminidi, etc. This method, of course, depends largely upon the flatness of the egg. The Micropterygids and Adelids are provided with a most complex cutting apparatus, with which they cut out pockets in a leaf, and then insert an egg (or eggs) within the THE OVUM OR EGG. ifs) pocket, in the soft cellular tissue of the leaf. Sufficient examples have been given to illustrate the almost endless variety that exists in the ego-laying habit among Lepidoptera. The egos of Lepidoptera are usually laid upon or near the food- plant of the larva, but this is not always the case. T'riphaena pronuba frequently chooses a piece of wire (in a fence), or cord hanging loosely in a garden, for the purpose. Riding reports batches of eggs of this species in two successive years (1895, 1896), on the meshes of a lawn tennis net. Chrysophanus phlaeas and Polyommatus icarus frequently deposit eggs on objects adjacent to the food-plant, so also, more rarely, do Pararye egeria, P. megaera and Pieris napi. Many ground feeding Noctuids lay on the stems of dead plants, leaves of trees, etc., and so also do Arctia catia, Spilosoma menthastri, and many other Arctiids. Riding records the finding of eggs of Macrothylacia (Lasiocampa) rubi on the trunk of a pine, at a height of nearly six feet from the ground, whilst a couple of the linear leaves of a Weymouth pine were girdled by 70 or 80 rows (10 eggs in each) of the eggs of a Noctuid moth, which turned out to be those of T'riphaena pronuba. Acidalia perochraria appears to follow the habit of the Hepialids, Melanaryia galatea, Pararge achine, etc., and to sprinkle her eggs on the ground. In the case of eggs laid naturally upon the leaves of deciduous trees or anuual herbaceous plants, the egg-stage is usually a short one. On the other hand, when the eggs are laid upon the stems, leaf- buds, ete., of plants, the egg-stage may last a considerable time. The former is the method usually adopted by Geometrids, Noctuids, Sphinegids and their close allies, although the Xanthids, Catocalids, Knnomids, ete., will occur to the mind at once as exceptions. It is remarkable that those eggs laid on leaves, and on grass stems are, as a rule, of a white, yellow, or greenish hue, whilst those on the twigs of bushes and trees are of a dirty white or grey, and frequently assume a purplish or red-brown tint, e.g., Thecla w-album, Ennomos autwnnaria, Lindromis versicolor, Tiliacea aurago, Cirrhoedia xerampelina, Dichonia aprilina, etc., and it will be found, as a general rule, that those species which hybernate in the egg-state, have eggs, which rapidly change to some dark hue that corresponds well with the colour of the stem or twig on which the egg is frequently deposited. Those that are scattered on the ground are usually of a dirt-colour, or have a pearly appearance; in fact, with a few apparent exceptions, the colour of lepidopterous eggs rapidly becomes such as to make them difficult of detection by the various predaceous creatures that prey upon them. The peculiar resemblance of a rouleau of the eggs of Lodis vernaria to a broken tendril of Clematis vitalba, the plant on which the eggs are laid, has already been noticed. ‘The easy way in which Tephrosia bistortata, Biston hirtaria, Amphidasys strataria (prodromaria), Orrhodia vaccinit, Dicycla oo, and their allies, pack their eggs deep into the bark crannies out of sight, attracts attention at once, because of the protection afforded. Anisopteryx aescularia, Kriogaster lanestris, Porthesia similis, P. chrysorrhoea and Porthetria dispar cover their eggs thickly with silky hairs from the extremity of the abdomen. Leucoma salicis covers its egos with a substance that has a salivary-looking appearance, but which is quite solidified, and various other devices have been developed by individual species for the protection of their eggs, and, as a rule, it appears probable that less destruction takes place in this, than in 14 BRITISH LEPIDOPTERA. the early larval stage of lepidopterous insects. It may be that natural selection protects one species more perfectly in one stage, another species in another stage, but, so far, young larve appear to be the particular form against which destructive agencies are most active. However well eggs may be protected, it is evident that consider- able destruction does take place in this stage, and it must be admitted, especially in the case of eggs laid in large batches, that if an attack thereon be made by some voracious entomophagous enemy, the de- struction is absolutely complete. Scudder records that ants destroyed the eggs of a Pyrametis cardut, that he had enclosed on a thistle. Spiders, ants and mites, are great offenders in this direction, but probably their combined destructive efforts fall much below those of the true egg parasites—minute Hymenoptera of the genera T'richo- granma and Telenomus—which lay their eggs in the ova of lepidopterous insects, and whose larve find sufficient nourishment therein to enable them to reach the imaginal condition. Nicholson mentions the rearing of 380 Telenomus phalaenarum from some eight eggs of Iacrothylacia (Lastocampa) rubi ; Bacot records the destruction of a whole batch of Arctia caia eggs by the same species, whilst Bignell states that he bred 2,100 imagines, of the same parasite, from 200 eggs of IM. rubi, an average of more than ten to each ege; Dimmock mentions the breeding of 830 hymenopterous parasites from a single egg of Smerinthus excaecatus. Numbers of parallel cases have been recorded in the various entomological magazines. The duration of the egg-stage varies greatly in different species. Buckell, Fenn and Prout have given** comprehensive lists of the duration of the egg-state in a great number of Geometrid species. The shortest periods recorded are two days, in the case of Acidalia virgularia, four days for Timandra amataria and other species. On the other hand, many species, that hatch the same year, pass a much longer period in the egg-state, e.g., Selenia tetralunaria, 23 days; Amphidasys strataria, 80 days; Boarmia abietaria, 19 days; B. gem- maria, 20 days; Hybernia leucophaearia, 88 days ; Larentia caesiata, 24 days, etc. In some species the length of time varies in different years, probably depending on meteorological conditions. Thus, biston hirtaria may take from 17 to 87 days; Hemerophila abruptaria, from 14 to 26 days; Selenia lunaria took 7 days in 1865, 12 days in 1861, and 15 days in 1886—all of the first brood. Selenita bilunaria has the following record :—1880, first brood, 16 days; 1888, first brood, 28 days, second brood, 16 days; 1890 and 1891, second brood, 15 days. But different broods of the same species may vary in the same year ; thus, in 1865, one batch of Camptoyramma fluviata took 5 days, another 10 days, and a third 21 days. Of those species which pass the winter in the egg stage, the time is so great that the combined larval, pupal, and imaginal periods are comparatively very short. Thus the egg stage of Mpione apiciaria lasts as long as 92 months; of Hnnomos autwnnaria, 72 to 10 months ; of Himera pennaria, 5 months; of Oporabia jiliyrammaria, 42 months ; of Cidaria testata, 8 months; of Chesias spartiata, 44 months. The ego stage of Thecla w-album and Zephyrus quercis lasts from July to early May; of Thecla pruni, from June until late April; of Plebeius aegon, from July to April; of Trichiura crataegi, from September to * Entom. Record, etc., iii., pp. 175-176; iv., p. 255; iv., p. 292. THE OVUM OR EGG. tS April; of the Catoealids, from July and August to April, and so on. The condition of the egg during the hybernating period is very interesting. In some species, such as Aryynnis adippe, Pamphila comma, Parnassius apollo, etc., the fully formed caterpillar remains coiled up within the shell all the winter ; in others, the eggs appear to remain until spring, almost in the same condition, so far as the con- tents are concerned, as that in which they were laid. Buckler records that eggs of Bombyx mori, Trichiura crataegi, Ennomos (alniaria) tiliaria, I. quercinaria, Cheimatobia brumata, C. boreata, Scotosia vetulata, Ptilophora plumiyera and Polia chi, have been examined from time to time until the middle of January, and nothing but the faintest traces of the future larvee have been detected by a microscopic examination of their still fluid contents. In the case of Tiliacea (Xanthia) awrayo, however, an egg was found to contain a partially developed larva on January 14th. It occasionally happens, as in the case of Polia wanthomista var. niyrocincta, that part of a batch of eggs, which should normally hybernate during the winter, hatches in the autumn, and the larve attempt to feed up, whilst the remainder of the batch goes over normally. It is recorded, also, that in a batch of Orgyia antigua eggs, the hatching takes place most irregularly, a few larvee appearing at a time, and the emergence of the whole brood thus spread over a long period. This happensalso in Hpione apiciaria, Lasiocampa trifolii, Catocalia species, etc. The influence that temperature has on the hatching period, and on the vitality of lepidopterous eggs, has been well shown by Merrifield. He has recorded that eges of Selenia bilunaria, and those of Selenia tetralunaria, were quite uninjured by exposure to a temperature of from 80° F. to 90° F., their development, on the contrary, being ereatly accelerated. Spring-laid eggs of S. bilunaria began to have their vitality affected after being ‘‘iced”’ (at a temperature of 32° I’., when they were in the central red stage), for 28 days, and none hatched after 60 days’ icing. The result was even worse with spring- laid eges of Selenia tetralunarvia, none of which survived 42 days’ icing, and some summer-laid eggs of the same species, exposed to the same conditions, fared no better. In all the experiments, up to 60 days’ exposure, nearly all the eggs, after being removed from the ice, matured so far as to admit of the formation of the young larva, which could be seen through the transparent shell. The failure was a failure to hatch. Standfuss has recorded that eggs of Arctia fasciata, Dasychira abietis, Odonestis (Lasiocampa) prunt and Dendrolimus pint, which were exposed to a temperature of 80° C. (93° F.), during the process of laying by the female, and up to the time of hatching, produced larvee in two-thirds or less of the normal time, and there emerged as perfect insects in the same year, é.c., without hybernation of the larva, in the case of A. fasciata, 71 per cent.; of D. abietis, 90 per cent.; of OU. pruni, 100 per cent.; and of D. pini, 81 percent. ‘The larve and pup of the broods were kept, as far as possible, at a mean temperature of 25° C. The eggs of the same females as those used in the above exper!- ment, which had already been laid at a normal temperature (22° C.), and were left in this until hatched, afterwards remaining in the same mean temperature of 25° C., as the other larve and pups, produced a considerably smaller number of perfect insects, without hybernation of 16 BRITISH LEPIDOPTERA. the larvee, viz., A. fasciata, 23 per cent.; D. abictis, 12 per cent. ; O. pruni, 64 per cent. ; D. pint, 28 per cent. It has been suggested that the sex of the imagines reared from eggs can be determined by the conditions in regard to abundance of food, or the reverse, under which the larve are reared; that, under a specially nutritious diet, lepidopterous larve tend to produce female imagines, whilst a starvation diet tends to the production of males. This, of course, assumes a neutral condition as regards sex in the newly-hatched larva, but the experiments that are supposed to have proved this simply show that male larve will stand more starving than those of females, or, in other words, that the minimum food which will allow male larve to just pupate, is, in the same species, often insufficient to allow the process in female larve, which die under such extreme treatment. The sexual organs of newly-hatched larve are moderately well-developed. Another theory which has been assumed, viz., that eggs laid suc- cessively by the same female are of opposite sex, has been entirely disproved, and experiment has shown that the relative proportion of the sexes is subject to immense fluctuation on the separate dates on which eggs are laid. As regards eggs laid on any one day, the sexes generally succeed each other in little groups of irregular size. It is further recorded that the pups obtained from different batches of Vanessa to had a large proportion of a certain sex, some batches pro- ducing almost entirely males, others consisting almost entirely of females. The eggs of Lepidoptera are developed in the ovaries of the parent, whence they pass down the oviduct into the vagina. In connection with the vagina are one or more pouches called receptacula seminis, in which the spermatozoa are stored after copulation. As the eee passes along the vagina to the ovipositor, the spermatozoa, or sperm- cells, are released from the receptacula, and certain of them enter the eee through the micropylar tubes, one of which fertilises the egg. Fertilisation, then, takes place at the time that the egg is being laid, by the spermatozoa entering the micropylar pores at the time that the ege passes the pouches. It is sometimes noticed that the latest-laid eges of a moth are infertile, a result probably due to the supply of spermatozoa being exhausted before all the eggs are laid. It is well- known that many Lepidoptera pair more than once. Anticlea ber- berata, Tephrosia bistortata, and various Zygenid species have been observed to do so repeatedly. No doubt, the habit is of common occurrence. CHAPTER III. EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. Iv may be well now to briefly consider the changes that take place in the fertilised ovum or egg, and that have, as their result, the pro- duction of an individual resembling its parents. These changes are of the utmost importance, and the embryological studies made by various entomologists have done much to throw light upon the wider biological problems which embryology presents. EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. 17 It is well known that all animals during their embryonic life undergo a series of remarkable changes, both in form and structure. The earliest embryonic appearance of widely different animals is such that it is difficult to say even to what class the embryo belongs, but as development proceeds, the characteristic features of the class are developed. When we come to consider the embryonic conditions of genera and species we find that the similarity of their early stages is much more pronounced, the likeness extending even to small matters of detail. It is possible to limit the study of the embryology of insects to the changes that take place within the egg, but it is well known that the larvee and pup of lepidoptera are essentially embryonic conditions, leading up to the production of the imagines. At the same time, their independent life, their competition in the struggle for existence, and the different conditions of their environment, have led to the formation of habits, and given rise to peculiar characters, which more or less obliterate, as it were, their true embryonic characters. It is necessary, therefore, in dealing with these stages (larval and pupal) to bear in mind two points:—(1) Whether the similarities which one sees are phylogenetic, that is, whether they are due to the transitory re-appearance of the characters of a bygone epoch in the ancestral history, or, (2) Whether they are cecological in their origin, and due to a similar relationship of the animals to their organic and inorganic environment. The characters manifested in the ege-state must almost of necessity belong to the first division; those in the active larval (considered as an embryonic) condition may belong to the first or second. It will be seen, then, that such phylogenetic conditions as the embryological stages of insects offer, indicate the lines of descent through which the species have passed. The complete study of em- bryology must, in time, give us much more correct notions of actual relationships than any other line of enquiry ; for it is highly probable that the embryonic stages show us, more or less completely, the lines through which the ancestral form has been developed, to produce the present condition of its offspring. It is to embryology, therefore, that we must look to furnish the clues to the true relationships which exist between animals, and a true genealogical classification can only be formulated by the aid of the knowledge which it contributes. We aim at obtaining a ‘‘natural”’ system of classification of insects, 7.e., an indication of the line of descent of the various species we study, and their connection with each other, and, hence, for this purpose, the structure of the embryo is often of more importance than that of the adult. Darwin says :—‘‘ In two or more groups of animals, however much they may differ from each other in structure and habits in their adult condition, if they pass through closely similar embryonic stages, we may feel assured that all are descended from one parent form, and are, therefore, closely related. Thus, community in embryonic structure reveals community of descent; but dissimilarity in embryonic development does not prove discommunity of descent, for, in one of two groups, the developmental stages may have been suppressed, or may have been so greatly modified through adaptation to new habits of life, as to be no longer recognisable. Liven in groups in which the adults have been modified to an extreme degree, community of origin is B 18 BRITISH LEPIDOPTERA. often revealed by the structure of the larve..... As the embryo often shows us, more or less plainly, the structure of the less modified and ancient progenitor of the group, we can see why ancient and extinct forms so often resemble, in their adult state, the embryos of existing species of the same classes... .. Embryology rises greatly in interest, when we look at the embryo as a picture, more or less obscured, of the progenitor, either in its adult or larval state, of all the members of the same great class.” We may now look briefly at the embryonic life of a lepidopterous insect from the time of the fertilisation of the ovum, until the larva hatches from the egg. This can only be done by the aid of a micro- scope. A very simple instrument with two lenses, a 2 and 4, is sufficient for ordinary purposes, although, of course, many other accessories are exceedingly useful. To get eggs for this purpose, take an ordinary glass tube and enclose a few females of some common Tortricid moth. These moths will usually lay their eges on the glass, and their eggshells are so trans- parent that the changes may be readily observed. Among the butter- flies, eges of Pararge megaera and Nemeobius lucina are not at all unsuit- able for observation. _ It is sometimes inconvenient to study the embryological changes which go on in an ege under a microscope, at the time that they actually occur. Two very good methods have been described in detail, by which the eggs may be killed and preserved for future observation. One of these is the distribution of the eggs in phials, one phial to be filled with carbolic acid, an ege put im, and the phial stoppered on each day, until the final one contains the newly-hatched larva. The other is to kill by heating in water at 80° C., then puncture the eges with a fine needle, and stain with ‘‘ Grenachar’s borax carmine”’ or ‘* Czochar’s cochineal.”’ It is an established fact of science, that every living being is evolved from a single unicellular germ. The egg in insects is not the earliest condition of the creature, because the primitive ovule can be traced back to the ovariole, or even to the primitive ovary, before the ovariole is developed. There is no need here to enter into the development of an ovum from the primitive ovary, as it is fully de- scribed elsewhere.** Suffice it to say, that the ovum at last is formed in the egg-chamber, and consists of a mass of yelk surrounded and embedded in protoplasm, and containing the female pronucleus, whilst at the time that the egg is laid, the main mass of it is made up of yelk-spherules. These spherules become granular, and the granules sradually replace the spherules, and are themselves again changed into yelk-cells, the probability being that they are thus changed in order to form suitable nourishment for the young embryo. At this time, the newly-formed blastoderm-cells begin to pass towards the circumference, leaving the degenerated yelk-cells in the centre. In addition to these yelk-spherules, the egg contains a homogeneous fluid, which has the ordinary composition of protoplasm, and consists essentially of the chemical elements, carbon, hydrogen, oxygen, nitro- gen, sulphur, phosphorus, lime, soda, potash, and other substances in minute proportions. The great characteristic of this Drotopme zi Entom. Record, vol. v., p. 212, EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. 19 fluid is its vitality, its ability to break up and sub-divide, to develop cellular structure, and to build up tissue from the cells produced by cell-division. After fertilisation, the protoplasmic fluid inside the Ovum remains in a homogeneous condition for a certain time; this varies for different species, but is comparatively constant in the same species. The first change that the protoplasm undergoes is that of the ordinary yelk segmentation, but, once this is set up, development continues generally with more or less rapidity. The segmentation starts at a point on the surface of the yelk called the ‘‘ first segmenta- tion nucleus,” and this nucleus undergoes cell-division in such a manner, as to form a superficial blastodermic layer. Side by side with this process of segmentation, the yelk separates from the outside cell- wall, and appears to become enveloped in a sac. The blastoderm layer (or layer of segmentation cells) has an elongated ventral plate formed in it, and in this the development of the embryo commences. This ventral plate broadens anteriorly, but the posterior part is divided transversely into segments. ‘This development is at once followed up by the formation of a longitudinal depression, the outer sac gradually enclosing this depression on either side, until, at last, the opposite sides of the epiblast, or outside layer of cells undergoing segmentation, unite over the depression, leaving it as a longitudinal tube. This becomes detached as a solid cellular mass, which splits into two longitudinal (mesoblastic) bands. At this period it would appear that the amnion is formed. Of this, Osborne says : ‘‘ After the yelk has become surrounded by the growth of cells called the blastoderm, and, after the germinal stripe, or foundation of the embryo, has been differentiated along one side of this blastoderm, a double fold of the latter grows up all round the cir- cumference of the germinal stripe, and finally closes in over it, the edges of the fold fixing together, and the two layers (of blastoderm) of which it is composed, at the same time separating from one another. The inner of these, continuous with the embryo itself, and lying im- mediately over it, is the amnion; the outer, continuous with the blastoderm surrounding the yelk, is the serous membrane. ‘Two sacs are thus formed, the one within the other, and between them lies the yelk. In the lepidopterous egg, the yelk next finds its way into the space between the amnion and the serous membrane, flowing over the former and depressing it and the embryo beneath it, till both are completely submerged in yelk, and consequently hidden from view.” After this the mesoblastic bands become divided into somites, and the first traces of the abdominal segments may be noticed, followed by the appearance of the three thoracic segments. The somites coalesce, and the common body-cavity thus enclosed, is called the celom. The three thoracic segments bear legs. The head, which appears to be formed of four segments, and the eye-spots, of which there are two clusters (each made up of six ocelli), placed one on either side of the second segment of the head, reckoning from the front, are then developed, followed in turn by the ventral prolegs. The inner part of the hypo- blast is absorbed to form the alimentary canal. The cells, now con- tained between the outside wall of the egg and the newly-formed alimentary canal, divide up into clusters, which are gradually differ- entiated into the various internal organs. The first of these to be formed is the dorsal vessel, which is so called because it is placed in 20 BRITISH LEPIDOPTERA. the dorsal part of the larva; this corresponds with the heart of the higher animals. The other organs gradually undergo differentiation, and the mouth organs also become developed. At this period of development faint pulsations of the dorsal vessel are discernible. The separation of the alimentary canal into an esophagus, a widened sac or stomach, and another contracted tube or intestine is clearly discernible, whilst the outer proteid part of the ege-contents is probably absorbed by cutaneous endosmosis. The trachez are developed from the spiracles inwards, but do not become visible until injected with air. Such are the broad outlines of the larval development within the ege. Froma tiny mass of protoplasm in the yelk of the egg, we get a larva produced such as we know it when newly-hatched. The egg- shell of most of our larger species is too opaque to allow these changes to be seen, but they can be readily observed, as we have already stated, in the eggs of Tortricids or Pyralids, owing to the thinness of the walls of the eggs in these groups. During the first stages of embryonic development, the ventral side of the embryo is external, or lies along the inner concave side of the egg, development commencing (as is usual in the Articulata and Vertebrata) on the ventral side of the insect. As development proceeds, the embryo changes its position, on account of the turning of the anal segment and its gradual upward movement, and that of the growing segments behind it, along the venter. In this manner the ventral part of the embryo gets turned towards the centre of the egg, whilst the dorsal part is turned towards the outside. Our observations of these movements were made on the embryo of Peronea (Tortrix) ferrugana. We found that when the embryo begins to show traces of segmentation, the thoracic segments are seen to develop three pairs of jointed buds or legs. At this time the embryo occupies a somewhat curved position, with the head slightly bent round towards the anal extremity, but with the legs outside, 7.c., the larva is bent back on itself so as to form a curve agreeing roughly with the curvature of the shell, with what afterwards becomes the ventral sur- face of the larva outside, and the dorsum towards the centre. The embryo then gradually changes its position, the anal segment curling round and being pushed by the growth of the preceding abdominal segments, slowly up the ventral surface of the larva; whilst the dorsum gets pusbed out, as it were, towards the centre of the egg. During this process the embryo becomes shaped something like the letter G, the movement continuing until a complete reversal of the embryo has been effected. The next stage is that in which the head and anus are in contact, each half running almost parallel, and this again is followed by an almost circular position, in which the dorsal area is now outside, and the ventral surface (with the legs) on the inside. The head, during all this time, scarcely changes its position. Very little further change in position takes place, the embryo, by this time, occupying all the available space in the egg. With regard to the change in position that the embryo undergoes in the egg, Chapman says that at the time that the ventral surface is towards the margin of the egg, the dorsal surface, or rather dorsal aspect, is still applied to the yelk-sac. At this time the dorsal sur- face is still broken by the umbilical opening, but, when the latter closes, EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. Pall the young larva is truly a larva, possessing no organic connection with the other egg structures, and may no longer be regarded as an appen- dage to the yelk-sac. The first use it makes of this liberty is to assume the S or pot-hook shape, continuing until at length its position is reversed, the dorsum being along the circumference of the ego and the venter being central. The head and tail sometimes merely meet (in the flattest eggs), sometimes slightly overlap, whilst in the dome-shaped eggs, the head so overlaps as to take, very often, a central position in the vertex of the ege, forming a dark spot there, as in Acronycta, Callimorpha, Hesperids, and many others. The essen- tial importance of this observation is that it shows that the em- bryonic position of the nervous system is the same in insects as in vertebrates, and since it must, therefore, be.identical also in the mature animal, it follows that the venter of insects corresponds, ana- tomically, with the dorsum of vertebrates and vice versé. Another important point with regard to this movement is, that whilst the larva is still truly an embryo, t.c., attached to the yelk and egg-structures, it has the venter outwards, but when the embryo becomes free, it moves as it likes, although this particular movement goes on so slowly, and without any apparent voluntary or even muscular effort, that it appears to be due to the mere force of the growth and development of the larva. During all this time, the disappearance of yelk has been taking place, but just when the embryo has attained its full growth, voluntary efforts to swallow are apparent, and the remainder of the yelk dis- appears. The remaining fluid is either absorbed by the larva through the skin, or evaporates through the shell; the trachez become visible by becoming filled with air, and the larva usually begins soon after- wards to commence eating its way through the shell. It would appear from Jeffrey’s observations* that the tracheze come rather suddenly into view, at the time that they are first distended with air. He states that ‘‘ the filling of the trachese commenced in the posterior segments, a sort of cloud gathering at the band where it is close to the head and in a line with the eye.” He says: ‘‘ I saw an apparently dark flood start from this spot, and, creeping along with a spasmodic effort, filling the branches, in its course, till it reached the head, and the whole of the traches became conspicuously visible on that side of the body.” The same observer describes how the dorsal vessel (heart) became visible in an embryonic Botys hyalinalis, on the tenth day after incu- bation. The pulsations were at first (8 a.m.) very faint and feeble, taking place somewhat irregularly at long intervals of 20 and even 30 seconds; but, after a few hours, they became more distinct, with shorter intervals between each beat, and became still more ac- celerated by the evening of the same day. ‘Two days afterwards, a beautifully clear view of the heart and its action was obtained, the pulsations being timed at 40 per minute, increasing to 60 a few _ minutes before the larva escaped from the egg. The important part played by the blood-tissue in larval nutrition, together with the supposition, entertained for many years by certain eminent naturalists, that circulation of the blood did not take place in * Ent. Mo. Mag., vols. xxii. and xxiii. 22, BRITISH LBPIDOPTERA. insects, has led to-considerable discussion. The origin of the ‘‘blood- tissue ’’ was worked out at length by Graber,* who concludes that the whole of the structures forming this ‘ tissue,” viz., oenocytes (certain cell-masses), fat-body and blood-corpuscles, are ectodermic structures. He further finds that the oenocytes are metamorphosed into the fat- body, and that the blood corpuscles arise from the fat-body, and, probably, also directly from the oenocytes. Wheeler,;+ however, looks upon the fat-body as a thickened part of the inner coelomic wall, due to an accumulation of fat-vacuoles in the cytoplasm of the mesoderm-cells.’’ He further concludes that the fat-body is not derived from the oenocytes, is of mesodermal, not ectodermal, origin, and concludes that there is no evidence for the origin of the blood from the oenocytes. Wheeler also remarks that—‘‘ Few insects appear to be better adapted for tracing out the origin of the oenocytes than the Lepidoptera. Thisis especially true of the larger Bombycid moths. That the segmental cell-clusters arise by delamination from the ecto- derm was conclusively made out in the embryos of Platysamia cecropia and Telea polyphenus. Hach cluster is several cell-layers in thickness, and lies just behind, and a little ventral to, an abdominal stigma. The succulent cells constituting the cluster are at first polygonal from mutual pressure, but, as the time for hatching approaches, they become rounder and more loosely united. I have not traced them through the larval stages, and merely record these fragmentary obser- vations because they completely confirm Tichomiroff’s and Graber’s observation on the origin of the oenocytes from the ectoderm.” The study of the lepidopterous embryo has given us many other interesting morphological particulars. Kowalewski found ten ab- dominal somites in the embryo of Smerinthus popult, all bearing pro- legs; whilst Tichomiroff detected eleven abdominal somites in the embryo of Bombya mori, all provided with prolegs except the first. Graber also found the abdomen of the lepidopterous embryo to consist of eleven true segments, and observed that the abdominal segments of Hutricha (Gastropacha) quercifolia were at first devoid of appendages, and that, when they did appear, they developed only on those seg- ments on which they persist in the adult. The mode in which the earliest development of the generative organs in the embryo of insects takes place is very obscure, but it would appear that the primitive ovaries are composed of a mass of cells, produced by an infolding of the ectoderm. Some writers, however, consider them to be derived from the mesoderm, whilst others trace their origin back to certain so-called pole cells, which originate even before the blastoderm is formed. However this may be, it would appear that they are, in that early stage, quite indistinguish- able from the other blastoderm cells. As development proceeds, the great mass of cells become differentiated into various structures, which subserve a special purpose, or perform a certain function. Certain cells in the ovary, however, retain their primitive condition, and, with it, the power, under suitable conditions, of forming another in- dividual of the same species. On this subject, Woodworth writes : ‘About the time of the completion of the blastoderm, the already * «Ueber die embryonale Anlage des Blut- und Fett-gewebes der Insekten,”’ Biol. Centralvl., Bd. ii., Nos. 7-8, pp., 212-224, + Psyche, vol. vi., p. 255 et. seq. EMBRYOLOGY OF A LEPIDOPTEROUS INSECT. 23 differentiated ventral plate infolds at a point on the median line about two-thirds from the upper end, and forms a very narrow pocket. The cells composing it look like the rest of the cells of the ventral plate at this time; they are almost round, and have a lining on one side, made of the grey matter. which originally bordered the whole egg, but which became a part of the blastoderm cells. The pocket remains open but a short time, but there is a long depression at the upper end of the bunch of cells. The mass of cells is soon cut off from the ventral plate, and they are then free in the body cavity, but remain in contact with the ventral plate at the point where they were produced. Later stages show that these cells produce the generative organs. The gerierative organs thus appear to be pro- duced by an infolding of the ectoderm, or possibly of the blastoderm, before the ectoderm is produced, but from a portion which is later to become ectoderm. The general idea has been that the generative organs in insects are produced from the mesoderm, although Metsch- nikow, as early as 1866, showed for certain insects a different origin.” Those further interested in the details of this subject would do well to refer to the writer’s chapter on the ‘‘ Embryology of a lepidop- -terous insect,” Hint. Record, vol. v., 1895. CHAPTER IV. PARTHENOGENESIS OR AGAMOGENESIS IN LEPIDOPTERA. Iv is generally necessary, among the Lepidoptera, that the two generative elements should unite before the fertilisation of the ovum can take place, and, since these elements are always developed in different individuals, it follows that copulation between the sexes is necessary for fertilisation, and for the subsequent production of young. It appears, however, that under certain conditions copulation is not necessary to ensure the production of young, since, occasionally, eges will produce larvee without the union of the sexes, and larve thus pro- duced have been recorded ag developing in the ordinary course into fully matured and fertile imagines. It is a well-known fact that, under ordinary circumstances, the eggs of almost all lepidopterous insects undergo certain changes after being laid. Some of these are common both to fertilised and unfertilised eggs, and since they must be looked upon as the outward sign of a change that is taking place within the egg, it is probable that the first changes which take place in the egg, i.e., the very first stages of embryonic growth, are independent of fertilisation. The changes which take place in the unfertilised eggs of some species are much greater than those which take place in others, and there are, as previously stated, cases on record in which development has proceeded so far, that the growth of the embryo has been completed, and a larva has hatched from the unfertilised egg. We see, then, that, under special conditions, nature produces progeny from virgin females without the intervention of the male. The production of such progeny among bees has long been known, 24 BRITISH LEPIDOPTERA. Vireil refers to it in the Georyics, and the old authors termed the phenomenon, ‘‘ Lucina sine concubitu.”’ It is now known as “aga- mogenesis’”’ or ‘‘ parthenogenesis.” It must be confessed that scientific experiments, conducted with sufficient care, relating to this subject, have been rarely performed, and that the evidence rests largely on chance observations. Still, there can be no doubt that some of the experiments, at least, have been sufficiently accurate to necessitate a scientific explanation of the phenomenon. Tt would be out of place here to discuss the general question of reproduction in the lower Invertebrates, a brief summary of which may be found, Hntom. Record., v., pp. 219 et seq. It need only be mentioned that fission or cleavage, gemmation or budding, and encystation are the more general means by which it is effected. In the Hydrozoa, reproduction is carried on all the summer by gemmation, but in the autumn, sperm cells and germ cells are produced in the same individual, the former fertilising the latter, which then become ova, in which stage these creatures pass the winter. ‘This method of sexual reproduction (i.c., with both sexes in the same individual) is very common in the lower animals, but among the higher invertebrates the sexes are usually differentiated in separate individuals, and, as a rule, coition is necessary for reproduction. This is the ordinary condition among insects. Among the Crustacea such species as Polyphemus oculus, Apus can- crifornus and Limnadia gigas consist, Newman says, almost entirely of female individuals, the presence of a male being the exception. Daphnia has males as well as females, but, according to Lubbock, the females appear equally prolific in the absence of the males. Newman also states that insome Arachnids the fertility of the female is not dependent on coition with the male. He instances [peira diadema, which he states invariably produced fertile eggs without union with a male. Among insects, the agamic reproduction of Aphides has long been well understood. This, however, is rather different from the partheno- genetic phenomenon presented by Lepidoptera, Hymenoptera, etc. In the former, viviparous young are produced by the females; in the latter, eggs are laid, and produce larve in due course, without the usual intervention of the spermatozoa. Most of the records of the occurrence of parthenogenesis in Lepi- doptera are, from a scientific point of view, most unsatisfactory, and based on chance observation, rather than on specially devised experi- ments. This is, perhaps, due to the fact that those entomologists who inbreed insects in the largest numbers, do so in order to obtain fine specimens for collections, and, as a matter of course, pair the females with males in order to ensure the due fertilisation of the eggs. It must also be borne in mind that, so far as our observations have gone, those species that show a parthenogenetic tendency, only lay a very few eggs in an occasional batch, that will produce parthenogenetic young. A very large number of female moths, therefore, would have to be sacrificed in order to obtain a very small number of parthenogenetically fertile eges. This does not apply, however, to the Psychids, where parthenogenesis, in some species, appears to be the rule rather than the exception. This has been clearly shown by Jourdan in the case of Bombya: PARTHENOGENESIS OR AGAMOGENESIS IN LEPIDOPTERA. 25 mort (Comptes Rendus Hebdomadaires des Séances de U Académie des Sciences, Paris, liii., 1861, pp. 1093-1096), where he remarks that it has long been customary, in the silk-producing countries of France, to regenerate a worn-out race by using ‘‘la graine vierge,”’ t.e., eg@s pro- duced from females that have not been paired with males. He details certain experiments made in 1851, which show the proportion of female moths that give fertile eggs parthenogenetically. From these experiments we learn that he had 300 yellow Milanese cocoons of a form of B. mori, that gives only one generation per year. The results work out as follows :—June, 1851—800 cocoons selected, each cocoon placed in a small cardboard box covered with gauze, so as to com- pletely imprison the moth on emergence. ‘The 300 cocoons produced 147 females and 151 males. The boxes containing males were re- moved and the females carefully preserved without being uncovered. Of the 147 females, six gave fertile eggs. ‘Two gave 7 eggs each, two others 4 eggs each, one gave 5 eggs, and one 2 eggs. These 29 eggs, preserved in their respective boxes without being uncovered, to render error impossible, hatched May, 1852. Many other eggs, it is men- tioned, passed from the pale yellow (colour when newly-laid) to the slaty-grey hue, which replaces the former after some days in fertile eggs. ‘The summarised results of this experiment worked out at :— 147 females, laid about 58,000 eggs, of which 29 produced larve, 7.e., about 1 : 2,000. Another experiment was made by Jourdan, in July, 1851, on white cocoons from South China, of a form of B. mori, giving five or six successive generations in one year. Fifty cocoons were separately isolated, as in the last experiment. From these emerged 23 females and 26 males. Seventeen of these females gave completely fertile eggs. One gave 113, and the least productive 12. The total number of eggs laid was 9,000, of which 520 produced larve. This gives a proportion of 1: 17. They hatched seventeen days after being laid. Although these experiments proved conclusively that some virgin females of B. mort could reproduce their kind without copulation, it was evident from the results, that the parthenogenetic reproductive power was exceedingly feeble. Of the two different races experimented upon, that with five or six successive generations per year was much more productive, parthenogenetically, than that with a single generation. One of the earliest essays on this subject was that of Von Siebold (translated by Dallas), entitled: On a true parthenogenesis in moths and bees. Siebold was led into his enquiries by some observations made on the reproduction of a species of Psychid moth, which, he noticed, propagated without copulation. He followed this up with observations on bees and B. mori, and found that the phenomenon of reproduction by virgin females was not at all uncommon. For this, he adopted the term “‘parthenogenesis,’’ which had previously been applied by Owen to the phenomenon now known as “ alternation of generations.”’ According to Siebold, we learn that the oldest communication relative to reproduction by female insects, sine concubitu, was made by Albrecht of Hildesheim, who (in 1701) relates that he found a brown pupa in a cocoon on a black-currant bush, and preserved it to see what moth would emerge from it. At the endof July, a moth of yellowish- white colour was disclosed, and in a few days laid a great number of eggs, and then died. In April of the following year, Albrecht was 26 BRITISH LEPIDOPTERA. astonished to find young black caterpillars in the box, instead of the eges. His communication to the Leopoldine Academy of Naturalists shows that he was satisfied that copulaticn had not taken place. In 1772, Bernoulli recorded that Baster had obtained fertile eggs from an isolated female of Gastropacha quercifolia, that had been bred from a caterpillar ; and further, that a caterpillar of Hpisena (Diloba) caeruleo- cephala, having changed to a pupa, the latter was left in a closed box, and that, about fifteen days after, he was surprised, on opening the box, to find, besides the enclosed moth, a family of young caterpillars, which had ‘already devoured the pupa-case of their mother, and a portion of their own egg-shells. Denis and Schiffermuller pointed out, in 1776 (Syst. Verz. der Schmett. der Wiener Gegend, etc., p. 2983) that these cases were possibly errors of observation; whilst Von Scheven considered that the larvee were probably from eggs laid by another female moth, previously confined in the same box. Siebold, being very dissatisfied with what was known about the subject, turned his attention to the ‘‘ case-bearers,’’ Solenobia lichenella and SS. triquetrella, and during the years 1850-1852 (the date of Jourdan’s experiments on 6. mori) he collected several hundred cases. None but females emerged from these-cases, and they commenced almost immediately to lay eggs. They ‘‘ possessed such a violent impulse to lay their eggs, that, when I removed them from their cases. they let their eggs fall openly. If I had wondered at the zeal for oviposition in these husbandless Solenobia, how was I astonished when all the eggs of these females, of whose virgin state | was most positively convinced, gave birth to young caterpillars, which looked about with the greatest assiduity in search of materials for the manufacture of little cases!”’ Parthenogenetic reproduction in Solenobia lichenella had also been observed by Wocke and Reutti. For many years the female of Apterona crenulella (Psyche helix) only was known,* and Siebold, to make sure that none of the ‘‘ wingless and footless moths ” were males, dissected many. He satisfied himself that all were females, and their unfertilised eggs were found to develop larve in the same ear. In 1795, Constans de Castellet, general inspector of the silk industry in Sardinia, had reported to Réaumur that he had reared caterpillars from unfertilised eges of Bombyx mort. ‘ Hx nihilo nihil fit,’ was Réaumur’s sceptical reply. Herold, in 1838, reported that amongst the unfertilised eges of b. mori, some here and there passed wholly or partially through the same changes as fertilised eggs, although they failed to hatch, and he distinguishes (Dis. de anim. vert. caren. in ovo formatione, Fase. 11., 1888, Tab. 7, fig. 31) between the foetus developed from fecundated, and that developed from unfecundated eggs, the former escaping as a larva, whilst the latter perishes in the egg- shell. He distinguished readily, also, various degrees of the faculty of development of unfertilised eggs, which manifested themselves by infinite differences in the disposition, number, form, and strength of the coloured portions of the egg. Herold was able to extract a foetus from one of these unfertilised eggs in the middle of winter. According * The male of Apterona crenulella (Psyche helix) was re-discovered by Clauss. He described and figured the larval case of the male, the difference between the pupe of the sexes, and the male imago in Zeits. Weiss. Zool., xvii., p. 470. Until then it does not seem to have been noticed since the time of Réaumur. PARTHENOGENESIS OR AGAMOGENESIS IN LEPIDOPTERA. 27 to Herold, embryos were not developed in all the unfertilised eggs examined, nor did he know of any case in which such embryos emerged from the egg. As far back as 1669, it may be mentioned that Malpighi was well acquainted (Marc. Malp. Diss. de Bombyce, Lond., p. 82) with these differences. He also then knew that the eggs of Lepidoptera were not fertilised at the time of copulation, but that each one was afterwards fertilised separately. Siebold quotes, on the authority of Filippi, that Curtis had received an isolated chrysalis of Telea polyphemus from America, from which a female emerged, all of whose eggs developed, adding that he believed a similar occurrence sometimes took place in BL. mori. Filippi relates that, in 1850, he observed the phenomenon in that variety of the latter species known as trevotini, which has three broods in a year. He also states that Griseri had also observed that many eggs of virgin females of B. mori developed. Siebold observes that various silkworm breeders in Breslau and Munich gave him similar information, and that he himself noticed exactly the same well-known change of colour, which took place in the fertilised eggs of this species, occurring in a large number of unfertilised eggs, although many stopped at various stages, only becoming reddish or violet, whilst only a very few went through the entire series of colour-change to slaty-grey. Siebold ob- tained no larve from them, but, in 1854, he received unfertilised eggs from Schmid, which produced larve. He tells us that he expected to breed only males, due to his having read Lacordaire’s account of Carlier’s observations, that ‘‘ he obtained, without copulation, three generations of Porthetria (Liparis) dispar, of which the last gaye only males, which naturally brought the experiment to an end.”’ Siebold, however, bred both males and females, which copulated freely, and appeared to have the ordinary amount of vitality. Kipp had pre- viously recorded the rearing of both males and females from some unfecundated eggs of Smerinthus popult. A brief summary of what has been observed in this country (with a few incidental outside observations) may now be useful. Newman in 1856, gave a list of Lepidoptera in which the phenomenon of par- thenogenesis had been noticed up to that date. These were :—Sphina ligustri, Smerinthus popult, S. ocellatus, Porthetria dispar, Psilura monacha, Diloba caeruleocephala, Telea polyphemus, Saturnia pyri, S. _pavonia, Orgyia gonostiyma, O. antiqua, Bombyx mort, Lastocampa quercts, Arctia cata, A. villica, A. casta, Dendrolimus pint, Cosmotriche (Odonestis) potatoria, Hutricha (Gastropacha) querctfolia, Sterrhopteria hirsutella (Psyche fusca), Apterona crenulella (Psyche helix), Canephora unicolor (Psyche graminella), Fumea casta (Psyche nitidella), Solenobia triquetrella, S. clathrella, S. lichenella. The observations on which this list were based are sometimes of a very unsatisfactory nature, but others are more convincing, e.y., Tardy’s experiments with L. querctis, in which three generations of perfectly vigorous and full-sized moths were reared without a single coition having taken place. Mory of Basle (Ent. Rec., vi., p. 209) recently obtained larvee from unfertilised eges of this species. A note in the Ent. Weekly Int., iii., pp. 175-176, states that parthenogenetic females of Solenobia inconspicuella had been bred, whilst in the Ent. Rec., vi., p. 89, Freer records the rearing of Talaeporia pseudobombycella parthenogenetically. Douglas (Substitute, p. 78) states that he has bred 98 BRITISH LEPIDOPTERA. Fumea nitidella from what he believed to be unfertilised eggs; the evidence, however, is here very unsatisfactory. Newman (Entom., ii., p. 28) records larvee from unfecundated eges laid by a female Phiyalia pedaria. These in due time became pup, but no imagines were reared. Haton (Hntom., iii., p. 104) records an instance in which parthenogenetic progeny of Orgyia antiqua were reared to the third generation. The details are:—First generation.—F rom a pupa found at Venn Hall, Sherborne, Dorset, in the autumn of 1864, a female imago emerged, which laid eggs. Second generation.—Of the above- mentioned eggs, ten hatched in the spring of 1865, but of these larve, one only, the largest from the first, came to maturity; this produced a female which laid eggs. Third generation.—Five larve from these eggs attained the pupal state of development, and one of them pro- duced a female imago by the middle of October. No further details are given. It may now be well to summarise some of the records under the various families to which the species belong :—Sotenosupes.—Solenobia tmeonspicuella, vide Ent. Rec., vol. vi., p. 5, where it is stated that par- thenogenesis in this species is well known. S. clathrella, mentioned by Newman in Phys. Characters in Classif., 1856. S. lichenella, Wocke anu Reutti (teste Siebold). S. triquetrella, Siebold’s experiments on this species, and S. lichenella, have already been detailed, see Hint. Rec., Vv., pp. 292-8. Talaeporia pseudobombycella, Freer, Ent. Rec., vi., p. 89, very many parthenogenetic larvee obtained. Psycuines.—Apte- rona crenulella (Psyche helix), was experimented upon by Siebold, and dissections of the parthenogenetic females were made. At this time, the male of this species was unknown. Canephora unicolor (Psyche yraminella) and Sterrhopteria hirsutella (P. fusca) are both mentioned in Newman’s list. Fwmea casta (nitidella) rests as a par- thenogenetic species, on Douglas’ unsatisfactory evidence. Noropon- tipES.—Diloba caeruleocephala, Bernoulli, 1772, records the hatching of unfertilised eggs. Notodonta dictaeoides. There is a record made by Alderson, as to the probability of this species being parthenogenetic, Eintom. Rec., vol.i., p. 96. Cerura vinula. Alderson notices unfertilised eggs of this species hatching, Hint. Rec., i., p. 95. LipartbEs.— Porthetria dispar, Carlier {teste Lacordaire), records three generations without copulation having taken place. Pearce, Hnt., xii., p. 229, obtained larvee May 6th, 1879, from unfertilised eggs. Weijenbergh, Archives Néerlandaises, v., 1870, pp. 258-264, records that fertile eggs of autumn, 1866, hatched April, 1867, and produced imagines, August, 1867 ; from these, without fecundation, eggs hatched April, 1868, and imaginesappeared August, 1868; from these, again, without fecundation, egos hatched in April, 1869, imagines in August, 1869; from these, without fecundation, eges did not hatch in spring of 1870, but dried up. Laelia coenosa. Brown, Entom., v., p. 395, an isolated female emerged, laid more than 50 eggs, which duly hatched and were sent to Hellins. Orgyia antiqua. Eaton, Hntom., 11, p. 104, data already given. O. gonostigma and Psilura monacha. Mentioned by Newman, Essay Phys. Charac., ete. ArcruprEs.—Arctia catia, A. villica and A. casta, are mentioned by Newman in his Essay Phys. Charac. Spilosoma mendica. Bowell, Ent. Rec., i., p. 174, obtained a batch of ova from female just out of pupa case, of which 15 hatched. Nocrumrs.— Anarta myrtilli. Watson, Hntom., xv., pp. 261-2, records putting a PARTHENOGENESIS OR AGAMOGENESIS IN LEPIDOPTERA. 29 pupa in a closed box, that the latter was opened some time after, and contained a female imago and many young larve, dead. Lasio- CAMPIDES.—Lastocampa quercius.—Tardy (teste Newman) bred three parthenogenetic broods of perfectly vigorous and full-sized moths. Mory of Basle, Soc. Hnt., April 1st, 1895, also records many larve from unfertilised eggs. JL. trifolit is recorded by Bouskell, Trans. Leices. Lit. Soc., iv., p. 422, as laying a few unfertilised eggs in 1896, which hatched in the following spring, and shortly afterwards died. Hutricha (Gastropacha) quercifolia. Baster (teste Bernoulli) ob- tained fertile eggs from an isolated bred female, Cosmotriche (Odonestis) potatoria and Dendrolimus pint, are both mentioned by Newman in his Essay Phys. Charac. Bompyciprs.—Bomby« mori. Many cases have already been dealt with at length. SarurnimxEs.—Saturnia pavonia. Noticed by Newman, Fssay Phys. Charac.; also by Bouskell, Trans. Leic. Lit. Soc., iv., p. 422, who mentions that a female laid six eggs in her cocoon, she being unable to get out ; these all hatched. S. pyri is mentioned by Newman, Issay Phys. Charac. Telea polyphemus. Curtis (este Filippi) obtained fertile eggs from a moth that emerged from a single cocoon in his possession, and that had come from America. Spxinemrs.—Smerinthus ocellatus. Newman, Mssay. Phys. Charac. Class.; Brown, Entom., v., p. 895; Headly, 7'rans. Leices. Tit. Soc., iv., p. 421, the latter mentions that of the eggs laid, 75 per cent. hatched. S. populi. Kipp (teste Siebold) reared both sexes from unfecundated eggs; Newman, Mssay Phys. Charac. Class.; Bouskell, Trans. Leices. Lit. Soc., iv., p. 421, mentions twenty out of seventy eges hatchimg. 8S. tiliae. Brown, Hnt., v., p. 395, no data. Acherontia atropos. Geddes and Thompson, Evolution of Sea, no data given. Sphinv ligustri. Newman, Essay Phys. Charac. in Classif. ; Nix, Hntom., iv., p. 3238, all eggs hatched in this brood. Cloge, Entom., v., pp. 856-7, fifty eggs hatched out of the brood. Gromerripzs. —Phigalia pedaria. Newman, Entom., ii., p. 28, records the laying of many eggs by three unfertilised females at end of February, 1864, and states that, on April 17th, the cage was swarming with newly-hatched larve. He failed, however, to get imagines. Although it may safely be assumed that parthenogenesis does occur in Lepidoptera, yet, as we have just said, it must be confessed that the material based on true scientific experiment is not large, and that many careful observations based on the most exact experiments are required. ‘The elucidation of the peculiar phenomena presented, is worth all the patience with which the entomologist must attack this subject, and he would have the reward of knowing that he had helped to make clearer one of the greatest mysteries of insect life. The phenomenon of parthenogenesis appears to me to be explicable only by supposing that the potency of the male element is handed down generation after generation, and that former fertilisations affect the embryo, independently of the actual union which fertilises the ovum. The male element must be looked upon as possessing, not only a great and direct influence on the development of the eggs im- mediately fertilised by it, but also on the eggs of successive issues not directly fecundated. That this is probably so, is shown by the fact that the unfertilised ege often undergoes varying conditions of deve- lopment, short of the actual development of a perfect embryo. This was foreshadowed in our notes on ‘‘ the ovum,’’ where the variation 30 BRITISH LEPIDOPTERA. and change of the colour of the egg are dealt with. In cases of par- thenogenesis, the influence must be powerful enough to cause full development, not only for one generation, but for one or more genera- tions beyond the one normally reached, and in this way may be explained the phenomenon that some species, which usually do not multiply without sexual intercourse, occasionally produce partheno- genetic young, even in cases like Sphinw ligustri, Bombyx mori, etc., where it could scarcely be expected. It is remarkable that, in most orders of insects, the parthenogenetic progeny is usually male, but, in the Psychidae among Lepidoptera, helotoky, or the production of parthenogenetic females, alone takes place. I may mention, in conclusion, that the great difference that exists between parthenogenesis (1) in the Psychids, where it appears to be, in some species, the rule rather than the exception, as it is in some Cynipids and in bees (as regards male eggs), and (2) in all other Lepi- doptera, where it is a rare and occasional phenomenon, is somewhat striking and important. This difference, no doubt, is only one of degree, but so great a degree as to be parallel to a difference in kind. It is quite possible, too, by means of the Psychids, to ally the partheno- genesis that takes place in Lepidoptera with that known to occur in the Cynipidae, and the phenomena might perhaps be brought into connection with a more primitive method of reproduction, e.g., gem- mation. I am quite clear that the modus operandi of parthenogenesis in Lepidoptera is still as obscure as ever, and that the explanation I have offered does not help matters much. It, however, is the only logical explanation that has occurred to me, and must be taken for, and only for, what it is worth. CHAPTER V. THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. Ar the time that the lepidopterous larva escapes from the egg, it possesses true insect characters. Its body is composed of a series of segments, containing the muscular, digestive, circulatory, respiratory, and nervous systems. It breathes by means of trachem, a series of fine tubes composed of an elastic membrane, and kept open by a spiral structure, which passes throughout their whole length. The four segments of the head are now welded into an almost inseparable whole, and, although the first three body-segments are assigned to the thorax, there is no well-marked separation between the thoracic and abdominal regions. The skin of the newly-hatched larva is very soft, but it quickly becomes harder, owing to the solidification of the horny substance called chitin in the outer cuticle. Usually larve have a somewhat colourless skin when just out of the egg; but the harden- ing of the cuticle is frequently accompanied by the production of a difference in colour, and by the development of the distinct markings which are characteristic of the larval cuticle, so that an almost colourless larva may, within an hour of hatching, become almost black, This hardening does not affect the sutures, and the interseg- THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. bl mental membranes allow the segments to move freely upon each other. The body segments are usually sub-divided into subsidiary rings or sub-segments, which also move more or less freely upon each other. The sub-segments are divided again into still smaller solid portions, which have a certain amount of freedom, and are technically called sclerites. A general description of a typical caterpillar or larva now becomes necessary. We find that the caterpillars of Lepidoptera are usually long and cylindrical, being, however, somewhat flattened on the yentral surface. ‘They may be considered as being composed of a head, thorax and abdomen, as in the imago or perfect insect, although the distinction between thorax and abdomen is not, as previously noted, distinctly marked. The cylindrical shape of the larva depends upon the fact that the larval skin contains fluid under considerable pressure. The head is a somewhat horny, compact, oval case, and is furnished with a number of appendages about the oral opening. It is made up of four (or more) segments, which, however, are not distinguishable after hatching. On each side of the head are, usually, six simple ocelli, arranged in lunular form on the cheeks. ‘Tle mouth consists of a labrum, mandibles, maxillee (with maxillary palpi) and labium (with labial palpi). The thorax is composed of three segments (those following the head), which are known as the pro-thorax, meso-thorax, and meta- thorax (or post-thorax) respectively. In all larvee which burrow under- sround or feed internally, and in many others, which do not, the dorsum of the pro-thorax is protected with a hard, corneous plate, often, indeed, extending to the meso-thorax and meta-thorax. Hach of the three thoracic segments bears on the ventral surface a pair of more or less horny legs (the true legs), which have five joints and terminate in a single claw. The abdomen consists of the last ten segments of the caterpillar’s body. ‘They are very similar, in general appearance, to the thoracic seoments, but the tubercles, or little chitinous hair-bearing knobs which they carry, are usually somewhat differently arranged, and they never give rise to true legs. Some of the abdominal segments, however, bear on their ventral surface a pair of stout fleshy protuberances, called pro-legs or claspers ; these prolegs are really extensions of the integu- ment, and have, on their free surface, a number of hooks. The number and development of the prolegs, and the arrangement of their terminal hooks vary considerably, different patterns distinguishing the several families, and even genera. Very little use is made of the true legs for purposes of progression, this being accomplished almost entirely by means of the prolegs. The terminal segment of the abdomen is known as the anal segment. On either side of the first thoracic, and of the first eight abdominal segments, is a tiny opening called a spiracle. ‘The spiracles are round, oval, or longitudinal in shape, and are the channels through which respiration is carried on. Reguiarly placed on certain parts of the body are to be found little chitinous, hair-bearing knobs (sometimes modified into fleshy elevations), which we have already said are called tubercles. These may give rise to single hairs, but sometimes to exceedingly close and dense fascicles. _ These tubercles are often strikingly modified at each successive ecdysis or change of skin. 32, BRITISH LEPIDOPTERA. The lepidopterous larva, by its active, independent existence, under- goes special modification and development, in order to protect itself from its various enemies. Hence the larve of different species assume, by modification, a manifold variety of shapes, and of arrangement of the various external structures—hairs, tubercles, etc. As the most specialised larvee present, therefore, such wide divergences from the original type from which they have sprung, it becomes necessary for us often to homologise the complex structures which they now bear with the simple structures from which they originated, and to do this a comparison must be instituted with those larve which, from the exigencies of their environment, are but little changed from the more ancestral larve. ‘The newly-hatched larve of many species, which are very specialised in their adult stages, have the specialised structures in a very simple condition, both as to form, structure and arrange- ment; whilst many boring and case-bearing larve are still more simple in the structure and arrangement of the tubercles, hairs and pro- legs, which are especially prone to be changed by external conditions. Larve which show this simple arrangement of tubercles, hairs and prolegs, are often spoken of as generalised, in contradistinction to those in which the structures are complicated, and which are termed specialised, larve. It must not be forgotten, however, that the most generalised of all lepidopterous larvee must be far in advance of the larvee of those insects (Orthoptera, etc.), with incomplete metamor- phoses. There can be little doubt that insects belonging to these orders, in which the metamorphoses are carried on within the ver narrowest limits, and in which the various stages present but little change, inter se, are much more ancestral than the insects belonging to those orders in which the metamorphoses are distinct, and in which the various stages bear but little resemblance to each other. The Lepidoptera which have the most generalised form of larvee are the Eriocephalids, Micropterygids, Adelids, Tineids, Sesiids, Psychids, Hepialids, Zeuzerids and the Tortricids. A comparison of these with each other, and with larve belonging to more specialised super-families, soon gives us a clue as to the lines on which modifica- tion has proceeded in the higher groups. Having glanced at the general structure of a lepidopterous larva, we may deal with a few of the organs in more detail. The head of a caterpillar is divided into two lateral halves by a suture, which divides, however, in the centre of the face, and leaves between its forked branches a triangular space. ‘This frontal triangle is termed the clypeus, and is very often distinctly and characteristically marked. Just within, and parallel to the central facial suture, is a deeply-grooved furrow, which is the reverse of a ridge that faces in- ternally, and to which the muscles of the head are attached. The true sutural line is but little developed in newly-hatched larve. Just below the clypeus is a short inconspicuous piece of chitin, welded to the clypeus. This is very distinct in some butterfly larvee (e.g., the Papi- lionids), andis known as the epistoma. ‘To its lower edge, the usually bi-lobed labrum or lip is attached by a fleshy hinge, enabling it to move freely backwards and forwards upon the mandibles. These latter are arranged on either side of the mouth; each consists of a stout, swollen, short, horny, plate, which is broader at the base, and becomes somewhat pointed at the apex, which varies considerably in different THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 30 species. In some, the apex is chisel-like ; in others, serrated ; in yet others, pointed. Below and behind the mandibles or upper jaws are found the fleshy bases of the maxille or lower jaws, each of which bears a short fleshy joint, to which the maxillary palpi are attached. The inner palpus consists usually of only one or two joints, and is in- conspicuous; the outer is more conspicuous, and consists of three joints, of which the two outer are somewhat horny and minute. The under surface of the head, lying between the basal portion of the maxillx, is occupied by the labium or lower lip. The labium bears, near its tip, on each side, a pair of minute two-jointed palpi, which, from their position, are termed the labial palpi ; their basal part is long, and the upper very minute. The apex of the labium is strangely developed into a small horny tube, from a hole in the tip of which the fluid which is secreted, and which ultimately forms silk, is passed, the tube itself being known as the spinneret. In the caterpillar, the antenne are very small and ill-developed. ‘They consist of a pair of four-joimted organs, one on each side of the face, placed just outside the base of the mandibles. The basal joint of the antenne is large and fleshy, the remainder being much more slender, and varying somewhat m shape. The third joint usually carries a long bristle. On each cheek are to be seen the six ocelli, placed just above the base of each antenna ; each one looks lke a smooth, hemispherical, protuberant wart, and they vary in colour in different species. Five of them form, usually, a somewhat regular curve, and are placed close together, whilst the sixth lies a little further away, often towards the centre of the cheek. As may be expected, the detailed characters of the head-parts vary somewhat in the different super-families of the Lepidoptera, but the general characters hold good. The head, too, varies greatly as regards the clothing and secon- dary organs that it bears. Ib is usually more or less tuberculated, the tubercles bearing hairs, and there can be no doubt that an aginiel ontogenetic relationship exists between these and the tubercles of the body seements. ‘The head segment nearest to the thorax, which forms the summit of the head, is sometimes ornamented with long pointed chitinous horns, spiny tubercles, ear-like processes, etc., all of which are prolongations of the corneous head structure. These undergo as varied and as different changes at each exuviation as do those of the body segments, in which simple hair-bearing, warty tubercles become developed into most complicated structures as some larvee approach maturity. We have already stated that the head is composed of at least four seements. We are so accustomed to look for organs in all animals having a somewhat similar function to analogous parts in our own body, ‘that it is easy to overlook their real morphological significance. There can be no doubt that in insects the mouth proper is a simple hole, and that the mandibles, maxille, etc., are simply modified appen- dages on the various segments of which the head is builtup. We may see how the modification has been brought about by a careful study of the limbs of a Crustacean (e.g., a crab or lobster). The mouth-parts, it is clear from such an examination, are undoubtedly limbs, modified first to hold, then to break, and lastly to masticate, the prey. Ideally, the head is made of several segments, each bearing a pair of organs— labrum, mandibles, maxille, labium—which are homologous with the true legs, C 34 BRITISH LEPIDOPTERA. Scudder draws special attention to the confusion which has arisen among entomologists as to the application of the terms ‘‘ maxille”’ and ‘‘ maxillary palpi.’ He says that ‘ideally, and sometimes actually, the maxille of insects bear three palpi, any one of which may become specially developed and receive the name of maxilla, while the others are termed palpi, thus the organ called maxilla in one group is not always strictly homologous with that which bears that name in another group. The segments of which the thorax and abdomen are composed are very much like one another, especially in the earlier stages, but they sometimes become considerably modified in size, shape and appearance, as the caterpillar gets older. The segments, both of the thorax and abdomen, are usually more or less distinctly subdivided transversely into sub-segments or annulets. The first thoracic segment is some- times considerably modified, constricted in Hesperid larve so as to form a neck, swollen in the larve of Lycenids, Papilionids, and many moths, so that the head is quite retractile. In Papilionid larve, also, it bears on its dorsum a forked scent-gland or osmaterium, hidden in a narrow transverse slit when not in use; in the larve of butterflies, Notodonts and Noctuids, it frequently bears on its lower surface a remarkable structure, known as the ‘‘ chin-gland.”’ This is an eversible gland, and one modification of it is found in the syringe of the Dicranurid larve. This, the larva of Cerura vinula uses as an offensive weapon, ejecting formic acid from it with considerable force. Of the abdominal segments, the last, the anal segment, is the most modified. The spiracles or stigmata, as we have already seen, are placed in pairs, one spiracle on each side of the first thoracic and first eight abdominal segments. Chapman was the first to discover that they were, occasionally, found in lepidopterous larvee on the second and third thoracic segments. Packard afterwards discovered the clustered tracheal tubes, belonging to these segments, in a Sphingid larva, and in that of Platysamia cecropia, but without any external sign of the spiracles. Scudder found spiracles on the second and third thoracic segments in the young larva of Pamphila mandan. The cause of the usual absence of spiracles on the meso- and meta-thorax, is probably due to the fact that, on these segments, the future wings are, during the larval existence, in process of development. Chapman observes (Ent. Rec., ix., p. 219) that, although there is no larval spiracle on the meta-thorax in Charawes jasius, yet, when the larva undergoes its final ecdysis, and becomes a pupa, a tracheal lining is drawn out between the 2nd and 8rd thoracic segments, where the imago has, but the larva has not, a spiracle. Chapman states that, although the casting of a tracheal lining from the 2nd thoracic spiracle had not been observed by him before he saw it in this species, he had inferred that such occurred, because he had seen it many years ago in numerous larval moultings (first, in the large silkworm, Antheraca yama-mat). and had also demonstrated the existence of this spiracle in the imagines. The spiracles are placed laterally, usually, a little below the middle of the sides, in the centre, or a little in front of the centre, of the seg- ments of the abdomen. ‘The pro-thoracic spiracle is placed near the hind margin of the pro-thorax. They are sometimes very distinct, at other times inconspicuous, usually with thickened lips, frequently of an oval shape and with a raised outer margin. ‘The spiracles on the THE EXTERNAL STRUCTURE OF. THE LEPIDOPTEROUS LARVA. 35 first thoracic and eighth abdominal segments are sometimes larger than those on the other segments. This is supposed to be due to the fact that the air-tubes from these spiracles ramify over a greater area of the body than do those from the others. The tubes or trachew which branch from the spiracles, carry air to almost all parts of the body. The tracheal tube, or atrium, which leads into the body from each spiracle, is provided with a muscular apparatus for excluding foreign bodies, and for the control of the admission of air into the tracheal system. ‘These are, as it were, muscular valves, and Landois describes the mechanism for this pur- pose as consisting of four principal parts—the bow, the lever, the band, and the muscle. The contraction of the latter, acting on the lever, causes the band and bow to meet and thus to close the passage. When the muscle relaxes, the natural elasticity of the parts causes them to separate again, and thus leave the tracheal tube open. The spiracle, then, leads into the atrium, which passes, by means of a muscular valve, into another chamber or vestibule, which, by means of another valvular arrangement, leads into the tracheal tubes proper. Lowne con- siders that the vestibule acts as a pump to force air into the trachez. The true legs of insects are prolongations of the body wall, and consist of :—(1) The tarsus (or foot). (2) The tibia (or shank). (8) The femur (or thigh). (4) The trochanter. (5) The coxa (or base). The lepidopterous caterpillar has three pairs of true legs, one pair being attached to each of the thoracic segments. ‘They are five- jointed, the two basal joints being, usually, larger than those which follow ; these joints are of a fleshy structure, whilst the three beyond are leathery or horny. The terminal joint is armed with a small, usually curved, simple unguis or claw. Packard states that, besides the terminal claw on the larval foot, there is apparently a second rudimentary one at the base, which he calls a spine-like ‘‘ tenant hair,’’ and sometimes also flattened lamellate seta. The use of the claw and tenant-hair, as grappling organs, is quite apparent; the use of the sete (which may be identical with Chapman’s ‘“ battledore palpus’’) is not known. The prolegs are also extensions of the integument, and consist, usually, of two large, stout, fleshy joints, which are generally retrac- tile within each other and the body-wall. The character of the pro- legs is very important, and the arrangement of the hooks which termi- nate them has recently been shown to have a distinct bearing on the relationships of the various super-families of the Lepidoptera, and to give important clues to their lines of evolution. In butterfly larve there is usually to be found on the inner side of the tip of the prolegs a pair of thickened pads, which move laterally. These usually bear a row of minute, but in some instances, very powerful hooks. The prolegs are found in most lepidopterous larve on the third, fourth, fifth, sixth and terminal abdominal segments, the last or anal, pair, passing both downward and backward, and being, sometimes, more plentifully supplied with little hooks than the other prolegs. These hooks are embedded in the skin, and are arranged usually in three rows, of which, however, sometimes only one and sometimes two are developed. ‘The hooks can be apparently extended at will, and the tip of the foot, between the pads, may be so inflated in some butterfly larvee as to bring the rows of hooks outside, and then the 36 BRITISH LEPIDOPTERA. pads can be opened and shut, so that the larva can cling with great tenacity to anything upon which it is resting. Among the moths the arrangement of these hooks appears to follow well-defined, general rules. Chapman has discovered that the prolegs of the ordinary external- feeding larvee of the Leprpoprera-HEtTEROcERA are essentially of two types, which he calls respectively the ‘‘ Macro,’’ and the Pyraloid or ‘‘ Micro” type. The former has a series of hooks on the inner side of the ventral prolegs only, and this appears to be characteristic of exposed-feeding larve (Sphingids, Bombycids, Nolids, Noctuids and Geometrids). The Anthrocerids (Zygzenids), although classed as IncompLetm, have prolegs of the ‘‘Macro”’ type. ‘The latter (Micro type) has a complete circle of hooks to the ventral prolegs, and appears to be characteristic of concealed-feeders (Pyralids, Phycids, Crambids, Gelechiids, Plutellids, and Cicophorids). The most remarkable pro- lees are those of the ErtocepHatipEs. In the larve of these moths, eight of the abdominal segments bear a pair of minute jointed legs of the same type as the thoracic. Chapman thinks that he finds some suggestion of the probable development of prolegs and their hooks in the Adelids—Nematois fasciellus and Adela rufimitrella. In the larve of these species there are ‘‘series of chitinous points beautifully arranged in rows, like the teeth of a shark, toe larger in front, those in each row alternating with those in the next rows, and gradually getting smaller, till they merge in the fifth or sixth row, in the ordinary integumental points. In the ordinary position of each proleg there are two sets of points facing each other along a transverse line. In Jncurvaria muscalella, the prolegs have two rows of hooks facing each other in this way along a transverse line. In J. (Lampronia) capitella, the young larva has no hooks, but the full-grown larva has hooks placed in a circle, yet with gaps showing that they are still an anterior and posterior set. In the Tortricids, the row of hooks is usually double; that is, there are longer and shorter hooks, but they are always in one perfect row; but, in other families, we find that traces of the multiple row of Nematots persists. This is the case in Hepialus. In the Sesiids, again, the circle of hooks is flattened antero-posteriorly, and is weak or wanting at the outer and inner ends, showing a relationship to Incurvaria. The anal prolegs very rarely have more than the anterior half developed. In Hepialus the circle is fairly complete. The Crambids have hooks of alternate size, like the Tortricids. Crambus often has three sizes of hooks alternated in one row.” Attention is also drawn to the fact that the larvee of the Hesperids show, in their three rows of hooks, a persistence of Adelid (or, at least, very low) structure, whilst the adult larvee of the true butterflies have the same structure as the true ‘« Macros.” The same observer finally concludes that ‘‘the proleg seems to reach its full development with a complete circle of hooklets. A higher development of the insect is not only accompanied by a fuller deve- lopment of the inner half of this circle, but also by the degeneration and disappearance of the outer half. This may often be followed out in ‘ Macros,’ usually among the butterflies, where the young larva has ‘Pyraloid’ prolegs, which often suddenly (at one moult), or more gradually (in two or three), assume, in the full-grown larva, the THE EXTERNAL STRUCTURE OF THE LEPIDOPTHROUS LARVA. 37 unilateral ‘Macro’ type’ (Trans. Ent. Soc. London, 1898). Prout has noticed that, in the Geometrid genus Oporabia, the newly-hatched larva has a complete circle of. hooks. We have already mentioned that the segments which usually bear the prolegs are the third, fourth, fifth, sixth and tenth abdominal. The Geometrids, however, usually have them only on the sixth and tenth abdominal segments. In the early stages of many Noctuid larvee, we find, however, only the merest traces of prolegs on the third and fourth abdominal segments; these, however, usually develop com- pletely at the later ecdyses. The peculiar method of progression, characteristic of Geometrid larvee, is due entirely to the absence of the prolegs on the third, fourth and fifth abdominal segments, and those Noctuid larvee which do not develop prolegs on the third and fourth abdominal segments, until late in life, resemble the Geometrid larvee in their mode of progression, whilst a whole group of Noctuid moths, which never do develop them, retain the looping habit throughout, and have been called, on this account, by some entomologists, Hxm- GEOMETERS. In some Geometrid larvee, prolegs appear on other than the abdo- minal segments normally carrying them. The larva of Himera pennaria obtains a pair of ill-developed ones, on the fifth abdominal segment, at the first moult; these persist after the second and third moults and disappear with the fourth moult. In larve of Anisopterya aescularia, prolegs are developed on the same segment, but these continue through- out the whole larval existence. The larva of an American moth, Lagoa crispata, described as being like a hairy Limacodid (Heterogenea) larva, with the head retracted, the body short, and the legs so rudimentary as to impart a gliding motion to the caterpillar when it moves, has seven pairs of short abdominal prolegs, the second and seventh abdominal segments each bearing a pair of rudimentary prolegs, in addition to those which normally carry them. Burmeister found exactly similar prolegs on the second and seventh abdominal segments of Chrysopyya undulata. According to the figures of Kowalewski and Tichomiroff, the embryonic larve of Sphinw and Bombyx mort have, at first, a pair of prolegs on each abdo- minal segment, but half of these are absorbed again before the larva hatches. Some very peculiar methods of progression are to be noticed among the larve of certain species of lepidoptera, none, however, is more peculiar than that of the Cochliopodids, of which our two British species, Hetero- genea cruciata (asella) and Apoda avellana (testudo) are very fair representatives. Resting on the upper surface of the leaves of their food-plants, with the body inflated to form a dome-like structure, they look very little like lepidopterous larve, and bear, in fact, a strong resemblance to the pup of ladybirds (Coccinellidae). The almost evanescent character of the prolees makes progression on the smooth upper surface of a leaf difficult, and Poulton has suggested that the remarkable undulatory movement by which the Cochliopodid larvee now progress was due originally to the larve first walking ‘‘ with adhesive claspers,’’ that these gradually became shorter and broader, thus yielding increased support by extending the area by means of which they adhered. Finally the claspers, he considers, would be altogether lost, and the whole of the ventral surface, from which they formerly 8 BRITISH LEPIDOPTERA: UN projected, would take part in locomotion. The modification of the prolegs and the method of progression, is, without doubt, designed to enable the larva to move freely over the smooth upper surface of leaves, which it could not well do under ordinary conditions. The sticky condition of the abdominal surface supports this view, but there can be no doubt that they spin some small quantity of silk on which they walk, as do so many other lepidopterous larve. Besides the tubercles, which have fairly fixed positions on the seg- ments, the skin has, scattered more or less regularly over the body, little elevations, resembling, somewhat, a fine pile or covering of minute hairs. This pile is a very common feature in butterfly larve, is sup- ported by very minute papille, and is generally distributed with con- siderable regularity, usually in a transverse, though sometimes in a longitudinal, direction. It is, however, occasionally scattered irregularly all over the body. When itis arranged transversely, it is usually some- what closely related to the subsegmental divisions into which the seg- ments are divided. Bacot says that this pile, which appears something like a clothing of short pointed spines, is very common in lepidopterous larvee in their first skin, and, in some, is so fine that a one-fourth lens (or even higher power) is required to detect it. The minute spines or hairs are often only visible at a certain angle, or when the edge of the dorsum is silhouetted against a bright background. In some larve this coat is lost at the first, or at a subsequent, moult; in others, it persists throughout the whole larval existence, becoming just a trifle coarser at each moult. The larve of Dicycla 00, Dianthoecia carpo- phaya, and Taeniocampa pulverulenta (cruda), among many others, illustrate this phase of its development. Bacot is of opinion that primitive and secondary hairs are of different origin, the former arising from the primitive setz or tubercles, the latter from the minute hairs forming the pile just described. He is also of opinion that the bifid shagreen hairs of Smerinthus, the dense clothing of short secondary hairs in some Lasiocampids, the short pyramidal granulations of cer- tain Liparids, and the highly specialised secondary hairs of some butterfly larve, are evolved from the minute hairs, which in their simplest condition, form the pile above described. That this pile is found rather generally among larve is proved by the following, very incomplete, list furnished by Bacot. ZyemymEs :— Adscita statices and Anthrocera trifolii (both in first skin). Lastocam- PIDES: Trichiura crataegi. Bompycipes: Bombyx mori (very fine). GEOMETRIDES: Phorodesma smaragdaria (first stage, skin granular later). Puatypreryeipes: Drepana cultraria. Notopontipes: Letocampa (Pheosia) tremula (dictaea), black in first skin, no trace in second, except on horn, Diloba caeruleocephala (in first stage), Odontosia carmelita (faint traces in third skin), Phalera bucephala (in first and second skins, (?) developed into secondary hairs later on). -Liraripes: Dasy- chira fascelina (in first skin), Demas coryli (strong in first, small in second to fourth skins), Orgyia antiqua (distinct but fine), Lewcoma salicis and Psilura monacha (in first and second skins), Porthesia similis. ArctupEs: Spilosoma lubricipeda (first to third skins, small), S. fuligi- nosa (first and (?) third skins), Arctia villica (first to fourth skins), Callimorpha dominula (strongly developed), Huthemonia russula (first to fifth skins), Huchelia jacobaeae (first skin). Noxipes: Nola cuculla- tella (in later stages rather granules than prickles). NocrumpEs;: Hk EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 39 Acronicta leporina (slightly in first skin), Cuspidia megacephala (in fourth skin, very noticeable and long, almost secondary hairs), Pharetra euphorbiae var. myricae (first to third skins), Pachnobia leuco- yrapha (weak in first skin, no trace after), Triphaena pronuba, T. comes, T. fimbria, I’. ianthina (just traceable in first skin, then absent), Peridroma saucta and Ayrotis puta (first skin, very small), Dianthoecta carpophaga (to full-grown, very long), Taentiocampa miniosa (large and distinct in first skin, only traces after), 7’. gracilis (very fine, black, in first skin, no trace after), 7’. pulverulenta (strongly marked throughout), Calocampa exoleta (in first, no trace in fourth, skin), Aporophyla australis (absent, or exceedingly fine in first skin), Calymnia affinis (strong in first, small in third, skin, no trace later), Polia chi (slight traces in first skin), Dicycla oo (strongly marked throughout), Plusia festucae (present in third skin). Paprzionipes: Zephyrus quercus (strong when, and not until, full-fed), Aylais wrticae (strong, in early stages). Since the observations, on which this list is compiled, were made off- hand, and when studying other characters presented by the larve, it can be readily understood how common an occurrence is the presence of this pile in lepidopterous larvee. Bacot says: Most of the Noctuids lose the character very early, yet in some it persists strongly throughout the larval life. Dianthoecia carpophaga exhibits it from the youngest to adult stage, yet adult D. cucubali shows no trace of it. 7’. pulverulenta retains, but T. miniosa soon loses, it. Scudder believes that ‘‘ the use of this clothing is tolerably clear, since this pile must prevent the too rapid evaporation of the heat from the surface of the body, for, although caterpillars are classed among the cold-blooded animals, they, nevertheless, have an internal heat above that of the surrounding atmosphere, which originates from the activities of the organs and the respiratory functions, and which they would lose more rapidly but for this investing pile.”’ On the dorsum of the thoracic (and more rarely the abdominal) segments of the larva, a hard chitinous shield is found. This is par- ticularly noticeable in all wood-boring larve, such as those of the Cossids, Hepialids and Sesiids, as well as in Crambids, Tortricids, and many Noetuids and Tineids. It is, however, more general and most marked on the pro-thorax, and hence it is often spoken of as the pro- thoracic shield. Since this structure is equally well-developed in the larve of the Cerambycidae and other Coleopterous larve which also bore into hard substances, it appears probable that this hard chitinous plate serves to protect the head, and parts of the body underlying the shield, from injury. Its appearance, too, in larve belonging not only to different families of the Lepidoptera, but also, to different orders, suggests that it has been developed in response to the external stimulus supplied by continual friction, an excess of chitin having been deposited (or developed) by the hypodermal cells of the tergal arch of the pro- thoracic segment. It is not unusual to find the shield, in some form of decadence, in larve which now feed fully exposed, especially in certain Noctuids, and occasionally the shield is present in the first larval stage, but lost in the later ones. These occurrences generally take place in larvee some of whose allies have, or had, boring habits. The value of this shield to boring larve for leverage purposes must also be very great, since it gives a solid fulcrum for the head. The excessive 40 BRITISH LEPIDOPTERA. development of the dorsum of the pro-thorax in the larva of Cerura ap- pears to have no phylogenetic significance, nor any close connection with the chitinous pro-thoraci¢ shields of boring larve. It is certainly smooth and shining, but appears to have been modified independently, for protective purposes, in this particular genus. Still, its probable use for the moulding of its hard cocoon must not be altogether overlooked. The anal segment has caused much discussion as to its structure and homologies, especially with regard to the suranal plate, the infra-anal lobe, the paranal lobes and the paranal tubercles. The supra-anal, or ‘‘suranal,” plate of Packard, is the ‘‘podex” of Kirby and Spence, and both in its shape and ornamentation would appear, especially in Bombycid and Geometrid larve, to afford specific characters. It varies much, also, among the Notodonts and Satur- niids, and is especially well-developed in those larve which constantly use the anal legs for grasping, while the front part of the body is more or less raised. It appears to be correlated with enlarged anal pro- legs. According to Packard, this plate, morphologically, appears to ‘‘ represent the dorsal arch of the tenth or last abdominal segment of the body, and is the ‘anal operculum’ or ‘lamina supra-analis’ of different authors. This suranal plate is, in the Platyptericidae re- markably elongated, forming an approach to a flagellum-like terrify- ing appendage, and, in the larva of Aylia tau, forms a long, promi- nent, sharp spine. Its shape, also, in Cerura caterpillars, is rather unusual, being long and narrow. In the Ceratocampidae, especially in Anisota, Dryocampa, Hacles and Citheronia, this plate is very large, the surface and edges being rough and tuberculated, while it seems to attain its maximum in Sphingicam pa, being triangular, and Snug | in a bifid point” (Bombycine Moths, p. 25). The ‘‘ paranal lobes ”’ are the « homologues of the two anal valves observed in the cockroach, and occur in all, or nearly all, insects,” according to the same author. They are the ‘‘ valvule”’ of Bur- meister, and the ‘ podical plates’’ of Huxley. They are fleshy and papilliform in Geometrid larvee, and appear as if projecting backward from the base of the anal legs. In the larve of the Dicranurids they are similar, and each ends in a seta. : The ‘‘paranal forks” or ‘‘ es tubercles’ are two bristles arising from the end of a papilla, directed backward. They are found in the larve of most arboreal caterpillars, being especially well- developed in those of Notodonts and many Geometrids, whilst they are wanting in the larve of Noctuids, Sphingids, Rhopalocera (?), and some Geometrids and Incometerm (Micro-lepidoptera). In the American Choerodes, they are very large; so also are they in the larva of our common Uropteryx sambucaria, where they become papilliform and setiferous. Their use was discovered by Hellins. In his description of the larva of Cerura bifida, he writes of them :—‘‘ At the tip of the anal flap are two sharp points, and another pair underneath, which are used to throw the pellets of frass to a distance.” Packard has seen the frass pellets held by the two spines of the paranal tubercles in Cerura borealis, whilst Dyar says that he has seen the caterpillars throw their pellets, with the aid of these spines, away from them, so as to strike against the side of a tumbler in which they were confined. The ‘‘infra-anal lobe” is described by Packard as a ‘‘ thick conical fleshy lobe or flap, ending often in a hard chitinous point, and situated THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 41 directly below the vent. In appearance, it is somewhat like the ege- guide of the Acrydit, though the latter is thin and flat.’’ Its use is, evidently, to aid in tossing the pellets of excrement away, so that they may not come in contact with the body. Packard, in an article describing the larve of certain species of Cerura, gave it as his opinion, that the ‘‘stemapoda”’ or filamentous anal pro- cesses of these caterpillars were homologous with the anal prolegs of other Notodonts, and, to show this, figures the anal prolegs of Dasy- lophia anguina in its first larval stage. He points out, in his comparison, that it is intermediate in form between the normal anal proleg and the stemapod, and remarks that it ‘‘has no crochets, but the planta, of which the flagellum of Cerwra seems to be the homologue, is re- tracted, and the retractor muscles, one of which is divided, are much as in the filamental legs of Cerura. It, however, is not the general opinion of British entomologists that the stemapoda are modified anal prolegs. Hellins regarded them as ‘dorsal appendages, somewhat after the fashion of the anal spines of the larve of the Satyridae.” Packard discusses this view, and concludes :—‘‘ After repeated com- parisons of the filamental anal legs of Cerura with those of Macrwro- campa marthesia, and comparing these with the greatly elongated anal legs of young Heterocampa unicolor, as figured by Popenoe, and taking into account the structures and homologies of the supra-anal and paranal flaps, one can scarcely doubt that those of Cerwa are modified anal legs.” There appears to be no doubt whatever that Packard is quite right, and that the view hitherto held by British entomologists, is &@ wrong one. The ancestral lepidopterous larve probably lived, at first, on grasses and low growing plants, and the arboreal habit was possibly assumed at a comparatively late period of larval evolution. This view is fully borne out by the geological evidence, for it is generally considered that flowering plants and trees were probably developed in the Cretaceous or Tertiary periods, and that our present race of lepi- dopterous insects became evolved side by side with the great changes that then took place in the flora of the world. Many of the most highly developed groups of Lepidoptera—most of the Noctuids, Arctiids, Pierids, Satyrids, etc.—feed, even now, almost exclusively upon low plants, and we find that, amongst larvee with this particular habit, the caterpillar is usually devoid of spines, and smooth or covered with a short, dense, velvety pile, whilst the markings consist chiefly of longitudinal lines of various shades of ereen, grey, etc., running from the head to the anus, dorsally, laterally, and ventrally. There are, of course, many very hairy and spiny larvee that feed on low plants, but these live usually a more or less exposed life—neither hiding under leaves (like the Satyrids) nor stones (Noctuids and Crambids) by day—and the great development of hairs, pencils, spines and bristles, appears to be due often to the cater- pillars having changed their mode of life from a concealed to an exposed condition, the change having frequently been accompanied by a move from a herbaceous to an arboreal feeding ground. Just as the caterpillars of grass-feeding larvee are green or grey in colour, and are chiefly ornamented with longitudinal lines of various shades, so the larve of arboreal caterpillars—Catocalids, Geometrids, etc.—have their bodies usually of a grey or ash colour, ornamented 42, BRITISH LEPIDOPTERA. with dorsal and lateral humps, so that they may assimilate more readily with the colour of the bark of the tree upon which they rest, and to small twigs bearing leaf-buds, ete. But such larve as are particularly protected in this manner do not lead such exposed lives as do those which, by the modification of the tubercles and sete of the more generalised larvee, have developed conspicuous spines, pencils of hairs, etc., or those which, by the development of bright warning colours, ocellated spots, etc., present an inedible, or even dangerous appearance to the avian, and numberless other, enemies which surround them on every side. Those larvee which live upon trees, and trust for their escape to their resemblance to pieces of stick, etc., are sometimes remarkably tuberculated. This is particularly noticeable in the Geometrids and Notodonts. On the other hand, those larve which are arboreal, but which trust for their concealment to leafy abodes which they make and in which they dwell—such as the Tortricids, Pyralids, ete.—have retained, in many ways, much more generalised forms of larve, both as regards colour, markings and tubercles. The adaptation of exposed larve to their surroundings is also very remarkably illustrated in the case of many ‘“‘plume”’ larve. No better illustration is needed than the similarity of the dermal clothing of the larva of Aciptilia galacto- dactyla to the woolly covering of the underside of the leaves of burdock (Arctium lappa), whilst Miss Murtfeldt quotes a parallel case among the American “ plumes,”’ stating (Psyche, iii., p. 890) that ‘‘ there is a very close imitation in the dermal clothing of the larve of Leioptilus sericidactylus to that of the young leaves of Vernonia, on which the spring and early summer broods feed.”’ The inedible nature of hairs needs no demonstration. That many birds are able to eat hairy larve is no detraction from the general principle. The fact that some birds do eat hairy larve leaves un- answered the fact that there are numbers of birds that cannot; and, undoubtedly, many small insectivorous birds that would eat a Tortricid larva with gusto, and make no objection to its simple setiferous hairs, would object to a larva of Arctia caia, or that of Acronicta leporina. We may take it for granted that the ultimate use of spines and hairs is for protection, and further, that they have been stimulated in their development by natural selection, indicating to insectivorous birds that the bristly armature is inedible; yet it seems that we have hardly reached the bottom of the question, if we look upon the special develop- ment of the sete and spines as due to protective needs, arising either from the attacks of birds or parasitic insects, but that we yet require some explanation of the initial cause of the development of such spines and specially developed hair structures. Fritz Miller, in 1864, maintained that the so called metamorphoses of insects, in which these animals quit the eggs as grubs or cater- pillars, and afterwards become quiescent pups, incapable of feeding, was not inherited from the primitive ancestor of all insects, but was acquired at a later period. Brauer, in 1869, divided** the larve of insects into two groups, the ‘‘ campodea ” form and ‘“ raupen ”’ form. In 1871, Packard} adopted these views, and gave the name of “ eruci- * « Betrachtungen iiber die Verwandlung der Inseckten, etc.,’’ Verh. K. K. Zool. bot. Ges. Wien, 1869. + American Naturalist, September, 1871. THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 43 form larve’’ to the cylindrical larvee of certain Coleoptera (weevils, etc.), as well as to those of Diptera, Lepidoptera, and Hymenoptera, con- sidering that the larve of all these were the result of adaptation, and were ‘derivatives of the primary ‘campodea’ type of larva.” Lubbock practically adopted** Brauer’s views in 1873. In 1895, Packard considered} that, ‘‘ while the origin of the eruciform larvee of the Cerambycidae, Curculionidae, Scolytidae, and other wood-boring and seed-inhabiting and burrowing coleopterous larve in general, is plainly attributable to adaptation to changed modes of life, as contrasted with the habits of roving, carnivorous campodeiform larvee, it is not so easy to account for the origin of the higher meta- bolous orders of Diptera, Lepidoptera, and Hymenoptera, whose larve are all more or less eruciform.”” He supposes them all to have arisen independently from groups.belonging to the Neuroptera (in the modern sense), or to some allied but extinct group. In 1895, we suggestedt that the earliest forms of lepidopterous larvee were hidden, and probably internal feeders. This view is not shared by Packard, who suggests that the earliest type was ‘‘ allied to some Tineoid which lived, not only on land, but on low herbage, not being a miner or sack-bearer.” This conclusion is arrived at by his consideration of the remarkable changes in form of certain Tineoid mining larve, described and figured by Chambers|| and Dimmock.§ These larvee were those of the Lithocolletids, Gracilariids, etc., and we quite agree that these apodous forms of mining larve are the result of adaptation to their habits. Our own idea of the ancestral form was, and is, one more closely resembling those of Hepialus, Cossus or Zeuzera, but the point matters little. What most authorities are agreed upon is—that by the time the ancestral larva was essen- tially lepidopterous, it was provided with prolegs that bore terminal crochets or hooks, and with simple fleshy warts or tubercles bearing simple hairs. The various forms in which the crochets are now arranged on the prolegs, and the many modifications which one finds in the arrangement and character of the piliferous tubercles, must be looked upon as more recent developments. Meldola first suggested{] that the green colour of many cater- pillars was due to the presence of chlorophyll in their tissues, and the matter was carried much further by Poulton* in his experiments on the larve of certain species of the genus Smerinthus. Packard thinks that the cuticle was at first colourless or horn-coloured, and suggests that ‘‘ after habitually feeding in the direct sunlight on green leaves, the chlorophyll thus introduced into the digestive system, and into the blood and the hypodermal tissues, would cause the cuticle to become green,” whilst, afterwards, ‘‘ by further adaptation and by heredity, this colour would become the hue common to caterpillars.” In view of Poulton’s more recent experiments} it would not do to labour this point too much, and we are inclined to agree with him, that the effect is rather « phytoscopic ’ * than ‘‘phytophagic,’’ inas- much as the colour of the surface of the leaf, rather than its substance, % oo” and Metamorphosis of Insects, 1873. {+ Bombycine Moths of America, 1895. t Entom. Record, etc., Vii., p. 6. || American le ili., 255-262 ; Psyche, i., 81, 137, 227, etc. § Psyche, iii., pp. 99-10 q Proc. Zool. Soc. of London, 1873, p. 159. * Proc. Roy. Soc. Lond., 1885, Pp. 269. } Trans. Ent. Soc. Lond., 1892, pp. 294 et seq. 44 BRITISH LEPIDOPTERA. acts as the stimulus, and this view has been materially strengthened by his experiments on larve, such as Rumia luteolata, etc., which show so much initial variation in nature, that some are green and some brown. His observations on larve of this species, as well as on those of Ennomos quercinaria (angularia), Selenia lunaria, Crocallis elinguaria, Phigalia pedaria, and, above all, Amphidasys betularia, show conclu- sively that the colour of some larvee is much affected by the surround- ing environment, and hence, as a general conclusion, we must assume, as far as our knowledge at present goes, that the general green colour of those larvee which essentially live among green leaves, is due rather to the influence of the particular environment surrounding them than to any direct action of the chlorophyll, which is consumed with their food. Commenting* on these experiments, Poulton says :—‘‘ Of the colour changes we must distinguish two main kinds: (a) Changes in the colour of the true animal pigments, leading to various shades of brown, grey, etc. (b) The change to a green colour modified from plant pigment, in the food. When such a change of colour is possible, the true pigments are always superficial to the green, and cannot be retained without concealing the latter, the degree of concealment depending on the amount and distribution of pigment. Thus, in Amphidasys betularia, the true pigments are chiefly placed in the epidermic cells, the green in the subjacent fat, whilst in many others, the former are in the superficial layer of the cuticle, the latter in the blood, or sometimes in the lower layers of the cuticle. But the appear- ance of the green is not merely the removal of a screen, although this must occur ; in some cases, at any rate, it also means the formation of the green colouring matter itself.” Probably the first attempt at ornamentation in the lepidaptecens larva consisted of longitudinal lines. These usually consist of (1) The dorsal or medio-dorsal line (a line running down the centre of the dorsum, throughout its whole length). (2) Sub-dorsal lines (one on either side of the medio-dorsal line). (8) Supra-spiracular lines (one on either side above the spiracles). (4) Sub-spiracular lines (one on either side below the spiracles). Sometimes there is a spiracular line running along and including the spiracles. The medio-dorsal line (as such) is probably, occasionally, due to the alimentary canal showing through the skin. Itis certainly so in many transparent-skinned larvee ‘(Hphestia kithniella, etc.), and it is just possible that, whatever form its modifications may now take, it originated inthismanner. Weismann has concluded, from his studies of the Sphingids, that the sub-dorsal line arose before thespiracular, and Packard} shows how, after the sub-dorsal and spiracular lines are formed, others are rapidly introduced—and some may as rapidly vanish, as necessary features of certain stages— which, when they become useless, are discarded. Weismann, in his Studies in the Theory of Descent, has shown that the primitive markings of caterpillars were lines and longitudinal bands. He further shows that larval spots are formed by interruptions, ‘“‘ the serial atrophy,”’ of the lines or bands. Packard says: The lines, bars, stripes, spots, and other colorational markings of caterpillars, by which they mimic the colours and shadows of leaves, stems, etc., have evidently been, in the first place, induced by the nature of the food * Trans. Ent. Soc. Lond., 1892, pp. 458-459. Bombycine Moths of America, p. 15, THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. A5 (chlorophyll), by the effects produced by light and shade, by adaptation to the form of the edge of the leaf (as in the serrated back of certain Notodonts), by adaptation to the colours of different leaves and to the stems, since shades of greens, yellows, reds, and browns, are almost as - common in the cuticle of caterpillars, as on the surface or cuticle of the leaves and their stems, or in the bark of the twigs and branches. He also adds that probably many have observed that the peculiar brown spots and patches of certain Notodonts do not appear until late in larval life, and also Jate in the summer, or early in the autumn, contem- poraneously with the appearance of dead and sere blotches in the leaves themselves. This phase of the subject will be dealt with at length in a later chapter. Tactile hairs, defensive setz, locomotive setee, and spines of various kinds, occur in worms; these, too, often arise from fleshy warts or tubercles. It is, therefore, not at all unlikely that the ancestral lepi- dopterous larva was provided with piliferous warts, and that many of the specialised spines, etc., now found in lepidopterous larvee, are modifications of these ancestral simple structures. It may be safely assumed that spines, hair-tufts, etc., serve to pro- tect the organism from external attack, probably also to strengthen the shell or skin. That even the most complex spines are modifica- tions of the tubercular structure is evident if one examines the cast skin of a Vanessid larva when it has just been thrown off, and the pupal state assumed. Packard, in a long argument,* suggests that ‘‘it is not improbable that tubercles, humps, or spines, may have in the first place been developed in a few generations, as the result of some change in the environment during the critical time attending or following the close of the Palaeozoic, or the early part of the Mesozoic age, the time when deciduous trees and flowers probably began to appear.’ The same author refers to Darwin’s significant remark} that ‘organic beings, when subjected during several generations to any change whatever in their conditions, tend to vary,” further, that ‘variations of all kinds and degrees are directly or indirectly caused by the conditions of life to which each being and, more especially, its ancestors have been exposed’”’ (p. 241) and again, that ‘‘ changes of any kind in the conditions of life, even extremely slight changes, often suffice to cause variability. Excess of nutriment is, perhaps, the most efficient single exciting cause.” Referring to the geological fact, that in the Cretaceous period, the forests consisted of oaks, maples, willows, beech, poplar, etc., Packard assumes that, in all probability, the low-feeding caterpillars of that time began to desert the herbaceous plants to feed on trees, and that they then experienced sufficient change to induce considerable variation, and that, to a great extent, tree-feeding necessitated isolation. He thinks, moreover, that the change from herbaceous to arboreal feeding, not only affected the shape of the body, causing it to become thick and fleshy, but also led to a hypertrophy of the piliferous warts, common to all lepidopterous larvae. We deal with this at length, not because we are inclined to agree with its assumptions, but because no other explanation of the actual origin of the cause of the modification has been offered. * Bombycine Moths of America, pp. 16 et seq. + Variation of Animals and Plants under Domestication, 2nd Haition, 1888, 46 BRITISH LEPIDOPTERA. We find, in definite positions on the larval cuticle, small buttons of chitinous material called tubercles. These usually bear a structure, formerly termed a ‘‘ hair,” but to which the term ‘“seta”’ is now usually applied, since the seta is not morphologically equivalent or homologous with the hairs of mammals. These sete arise through a modification and hypertrophy of the nuclei of certain cells of the cuticle. According to Dyar, the “ primitive form of tubercle consists of a little chitinous button on the skin, bearing a single long hair. It is found in the less specialised groups of Lepidoptera, and exclusively in the Jucarm and the Psychids. When this form is present, there are, in general, no other hairs on the body.” It would appear that in the phytophagous Hymenoptera (Tenthred- inidae), there are well-developed setiferous tubercles, apparently more generalised than those found in any Lepidoptera, but in the Lepidop- tera there appear to be, according to Dyar, two types of arrangement. (1) By far the more generalised, consists, on the abdominal segments, of five tubercles above the spiracle on each side, three in a transverse row about the middle of the segment and two behind, whilst below the spiracle are two oblique rows, containing respectively two and four tubercles. This type is found in Hepialus. (2) The second type con- sists of two dissimilar lines of modification of the first type, of which the fundamental arrangement consists of three tubercles on each side above the spiracle; three more on each side, below or behind the spiracle and above the base of the leg; and three (or four) on the base of the leg on the outside, and one on the inside near the mid- ventral line. As Dyar has made himself quite an authority on these setiferous tubercles, it may be well to glance at his nomenclature. Commencing from the dorsum, he calls the tubercles above the spiracles i, ii, i11,* the three below, iv, v, and vit ; the group on the outside of the leg is known as vil, and the single one on the inside of the leg as viil. Tubercles vii and viii, Dyar says, are present also on the legless abdominal segments (1, 2, 7, 8 and 9), in a position corresponding to those on the segments bearing prolegs. On the last two abdominal segments (9 and 10) the number of tubercles is always less than the fundamental number, even in generalised larve. This is evidently due to the fact that these segments have been partly aborted, being without spiracles. The reduction of the ninth abdominal segment has taken place on the anterior portion, whilst the tenth abdominal has lost the lateral part (Classification of Lep. Larvae, pp. 196-7). Dyar’s conclusions as to the relationship which the lepidopterous super- families bear to each other are based on (1) The position of the tubercles with regard to the sub-segments into which the abdominal segments are divided. (2) The tendency for tubercles iv and v (the post-spiracular and sub-spiracular tubercles) to coalesce or separate. As to their position, Dyar says that in the Jucarm (Hepialids) the three tubercles of the middle sub-segment are all present, and the upper and lower of the posterior sub-segment. In the Psychids, the three tubercles are retained on the middle sub-segment, but both are * | = anterior trapezoidal, ii = posterior trapezoidal, iii = supra-spiracular. + This is a secondary tubercle, absent usually in the newly hatched (gene- ralised) larva of the higher families. Hence its importance is less valuable than Dyar afterwards insists, when discussing the Psychids and Micko-FRENATH. THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 47 lost on the posterior one; the sub-stigmatal tubercles are retained and approximated, the anterior one of the four on the base of the leg seems to have been moved up, forming tubercle vi, which is thus anterior (=pre-spiracular). This explanation accounts for the possible formation of the pre-spiracular tubercle as such, for it will be observed that, whereas tubercle v of Dyar is the typical sub-spiracular tubercle of the more specialised families, tubercles iv and vi, typically originating below the spiracle, according to Dyar, become respectively the post-spiracular and pre-spiracular in special instances. In all the other families of the Lepidoptera, Dyar states that the middle tubercle of the three on the middle sub-segment is lost, but the upper on the posterior sub-segment is retained; the two (iv and vy) below the spiracle are also retained, as in the Psychids, but they are either approximated (sometimes even united to form a compound sub- spiracular tubercle, as is Margarodia), or separated so as to form two distinct tubercles, viz., the sub-spiracular and post-spiracular, whilst of the four tubercles at the base of the leg, the posterior one (not the anterior one, as is the case in the Psychids) is moved up to form tubercle vi. The tendency for tubercles iv and v to coalesce so as to form a compound sub-spiracular tubercle, appears to be characteristic of the larvee which comprise, in its broad lines, Comstock’s MicrorrenatH or GENERALISED Frenat®, whilst the tendency for tubercles iv and v to separate and form post-spiracular and sub-spiracular tubercles, re- spectively, appears to be characteristic of his SprcraLiseD Frenarz. Dyar notes, and if it held good it would be very curious, that ‘‘ itis a striking fact that we do not find a series of intergrading forms between the single-haired tubercle and the many-haired wart, though both may occur in different genera of the same family,’’ and he considers that this is explicable on the principle of discontinuous variation, which is insisted upon by Bateson. He says that in the lower (more generalised) families we have the simple and primitive form of tubercle ; in the more specialised families we find a modification, which consists in the tubercles becoming enlarged and many-haired. In these compound tubercles each hair arises from its own minute tubercle, and the whole are borne upon an enlarged base or wart. Modification then takes place in the higher groups, by a reduction in the number of tubercles, the reduction taking place :—(a) By coalescence. (6) By unequal development and final obliteration of particular ones. (This is discussed later in chapter.) We have seen that in some of the more specialised larvee there is a general tendency to the reduction of tubercles, so that some may entirely disappear. In some cases, however, the bases of the tubercles are developed into long fleshy processes, carrying aborted setz, as in the case of certain larvz of the Nymphalids, Papilionids, etc. In other cases, the setae remain as glandular hairs, in some instances secreting an urticating (? odorous) fluid, or the hairs themselves become highly specialised, and greatly increased in number, forming brushes, tufts, plumes, etc., as in the larve of Acronyctids, Liparids, Arctiids, etc. One of the most striking modifications of the tubercles is seen in the caudal horn of the Spuinerpes. This is an unpaired dorsal process on the 8th abdominal segment. A figure of the larva of Deilephila euphorbiae (Weismann, Studies in the Theory of Descent, Pl. v., fig. 38) in its first skin, shows that the two setze of tubercle i are borne on the 48 BRITISH LEPIDOPTERA. apex of the caudal horn. This would point strongly to the conclusion that the horn represents the base of the unconsolidated pair of tubercles i, the tubercles themselves havine disappeared. This disagrees with Poulton’s view,** for he looks upon the caudal horn as representing the consolidated pair of tubercles 1 of the Saturniids. The caudal horn of the remarkable genus of Plume moths, Agdistis, does not, according to Bacot, rise from the 8th abdominal segment, and bear the anterior trapezoidals of that seement, as in the Sphineids, but is situated on what is either a small 9th abdominal segment, or a large and distinct subsegment of the 8th abdominal, both the anterior and posterior trapezoidals of the 8th segment being in front of the horn, and in their correct position relative to the spiracle. The production of a central row of dorsal tubercles apparently un- paired, in certain families, is very remarkable. This is well seen in the medio-dorsal row of spines in the adult larve of certain Vanessids, where, too, the real nature of the spines forming this row may be readily learned, by comparing the adult larvze with those in their earlier stages. They are formed by the union of tubercle i on each side, consolidating on the central line of the dorsum. A similar arrangement also occurs in the Saturniids. The modifications which tubercles and sete undergo have been tabulated by Packard.t His table reads as follows :— A.—TUBERCLES. a.—Simple and minute, due toa slight thickening of the hypodermis, : and a decided thickening of the overlying cuticle; the hypodermis contains a large unicellular gland, either for the secretion of the seta or for the production of poison. 1.—Minute piliferous warts (most Tineid, Tortricid and Noctuid larvee). 2.—Enlarged smooth tubercles, bearing a single seta (many Geometrid and Bombycine larve). 3.—Enlarged spherical tubercles, bearing a number of sete, either radiated or subverticillate (Arctians, Lithosians). 4.— High, movable, smooth tubercles, having a terrifying function (Schizura, Xylinodes, Notodonta, Nerice). i 5.—Low and broad, rudimentary, replacing the ‘‘ caudal horn” (Choero- campa, Leiocampa (Pheosia) dictaea, and L. dictaeoides). b.—More or less spinulose or spiny (disappearing in some Sphinges after Stage 1). 1.—Long and slender, usually situated on the top of the eighth abdominal segment, with microscopic spinules in Stage 1. (Most Sphingidae and Sesiat). 2.—Smooth subspherical warts (Chalcosia, Kast Indies) ; or elongated, but still smooth (Attacus atlas). 3.—Subspherical or clavate spiny tubercles of many Attaci; the spinules usually short. 4.—Spinulated spines or elongated tubercles of Ceratocampidae and Hemi- lucidae (Automeris io and Hemileuca maia, etc.). 5.—Spike-like hairs or spines (Samia cynthia, Anisota, Hypsa (KH. Indies), Anagnia). 6.—Antler-like spines. Harly stages of Heterocampa biwndata, H. guttivitta and H. obliqua). * Trans. Ent. Soc. Lond., 1888, pp. 568-574. + Bombycine Moths of America, p. 21. { Packard does not use Sesia in the sense usually understood in Britain, 7.e., for the true Clearwing moths, but as a synonym of Macroglossa, THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 49 B.—SEt# (HAIRS, BRISTLES, ETC.). 1.—Simple, fine, short or long, macroscopic or microscopic sete, tapering hairs, scattered or dense, often forming pencils (many Bombyces, Zygaenidae,* Noctuo-Bombyces, Apatelae). 2.—Glandular hairs, truncate, spindle-shaped or forked at the end, and secreting a more or less viscid fluid [many Notodonts in Stages 1 and 2; many butterfly larvee; Pterophoridae (in last stages) ]. 3.—Long spindle-shaped hairs of Apatelodes (Apatela americana), and Tinolius eburneigutta. 4.—Flattened, triangular hairs in the tufts, or on the sides of the body of Gastropacha americana, or flattened, spindle-shaped scales in the European G. quercifolia. 5.—Spinulated or barbed hairs (most Glaucopides, Arctians, Lithosians, Liparids and many Bombycids). C.—PsrUDO-TUBERCLES. 1.—Filamental anal legs (stemapoda) of Cerura and Heterocampa marthesia. 2.—The long suranal spine of Platyptericidae. Before leaving our consideration of the hairs of larve, it may be well to mention the spathulate hairs of Jocheaera alnt. These are usually erect and conspicuous, but in the adult stage are spread some- what laterally. Chapman gives them as measuring, in the 4th larval skin: on pro-thorax, 34 mm., on 5th abdominal, 14 mm., on 9th abdominal, 24 mm.; in the 5th larval skin, on the same segments 6, 34 and 4 mm. respectively, and in the 6th larval skin (extra moulter), 7, 4, and 41 mm. respectively. The larva of Hutricha quercifolia and those of other species possess remarkable scale-like hairs, as mentioned above by Packard. The study of the newly-hatched larva is one of the most important factors in considering the phylogeny of the lepidoptera, for it happens that many species which have the most specialised adult larve hatch in a very generalised condition, and hence, comparison of the tubercles in the newly-hatched larvee, with the more specialised structures that replace them afterwards, gives many valuable clues to the origin of the complicated structures of the adult. From this, it would appear, that the more primitive arrangement of the five chief tubercles and sete occurring on the abdominal segments, is such that the three tubercles above the spiracle exist as the anterior trapezoidal, posterior trapezoidal, and supra-spiracular tubercle, respectively, whilst the sub- and post- spiracular tubercles are both placed beneath the spiracle. Dyar remarkst :—‘‘ Curiously enough, the most generalised condition is ex- hibited in the first stage of the butterflies (Rhopalocera). This is to be accounted for by the fact, which was brought out by a comparison of the first stage of such genera as Danais and Grapta, with their later stages, viz., that the armature of the butterfly larva is not developed mainly from the primary tubercles, but almost entirely independent of them.” This is certainly too sweeping an assertion to comprise the facts re- lating to the armature of the Vanessid and Argynnid larve, and pro- bably some others. In many cases there can be no doubt that the armature is frequently developed from the primary tubercles, often, of course, with certain stages of the evolution left out. In some the process of development is comparatively simple, as may be seen, if the larva be * As used in America, this = our Huchromiidae, which are Arctiids, not the family British lepidopterists call Zygaenidae. + ‘* Additional notes on the classification of Lepidopterous larvee,” Trans. New York Acad. Sci., xxv., p. 52. D 50 BRITISH LEPIDOPTERA. examined carefully at each ecdysis. The case of Aglais urticae and others occur to me. The horn which characterises the Sphingid caterpillars is, as we have seen, placed on the dorsum of the eighth abdominal segment, and it is remarkable that when it is absent in allied forms, it is replaced by a small, low and flattened tubercle, the segment itself beimg somewhat swollen. Many Noctuid larve—Amphipyra, Mamestra persicariae, etc., have a prominent hump on this segment, so also have the larve of the Agaristidae, and others. In many Notodont larve the first ab- dominal segment bears a conspicuous hump, sometimes forked, often ending ina seta. It would appear, from Packard’s researches, that the three thoracic segments, and the first and eighth abdominal ses- ments, are those most usually characterised by tall fleshy tubercles, horns, etc. The same author shows that the first and eighth ab- dominal segments bear no prolegs, and that, when walking, these apodous segments are more raised than the others, and that, if it be true, as it appears to be, that these humps do frequently rise from the most elevated portions of the larva when crawling, then the move- ment of these conspicuous structures might tend to be of service in frightening away other creatures. He further suggests that the humping or looping of these segments may have had something to do with inducing the hypertrophy of the dermal tissues which enter into the formation of the tubercles or horns, whilst with regard to the mutant or movable tubercles, he suggests that the movement of these appendages would suffice to scare off an approaching ichneumon or Tachina. Larve are, of course, subject to the conditions involved by the struggle for existence, and to modification in relation to environment, and, hence, is due the modification of the setiferous tubercles, by which the larva is made to resemble different objects at different phases of its existence. Hvyveryone knows how different is the larva of Jocheaera alni* in its third skin, in what is known as the ‘‘ birds’-dropping ”’ stage, from the adult larva with its conspicuous bulbous-tipped hairs. This reference to a subject already discussed in a previous part of this chapter (p. 47) gives us a chance of explaining why we have thrown doubt upon Dyar’s statement that ‘“‘we do not find intergrading forms between the single-haired tubercle and the many-haired wart.’’ He probably had in mind some such change as that occurring in the Anthrocerids, in which the simple single-haired tubercle of the first skin becomes a many-haired wart in the second, increasing in size at each subsequent moult. It happens, as a matter of fact, that intergrading forms are exceedingly common in many species of Lepidoptera, a single-haired tubercle in the first skin ac- quiring some hairs at each subsequent moult, until it becomes a wart. In the Acronyctid larvee there are various stages in different species, even in the first skin, the differences extending from a one-haired tubercle, two-haired tubercle, etc., to a many-haired wart, and such cases are not at all uncommon. In the case of Anthrocera, it is pos- sible that some stages in the evolution of the many-haired wart are now missed, but, in others, the intergrading forms are, as we have said, by no means unknown. * Chapman, Entomologist’s Record, etc., vol. ii., p, 123, THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 51 The varied stages of development of the setiferous tubercles, some- times reached in allied genera in the egg, is of the highest significance, as is also their comparative development in the various stages of the larve of allied genera, as in Ornithoptera and Papilio, in Aglia and Citheronia ; whilst Packard** states that the ‘tubercles of the adult larvee of Saturnia (pavonia and pyri) are on the same plane with the embryo, just before exclusion, of the more highly specialised forms of the group Attacinae,” and, again, ‘whilst the late embryos of the Attacinae are, perhaps, paralleled by the fully-grown larva of Saturnia, the fully-grown larva of the most, or one of the most, generalised of the Attacinae, Platysamia, is on the same plane of specialisation as the larva of Callosamia in its third stage.”’ The larve of a large number of Lepidoptera are provided with what may be fairly termed glandular sete. They are more especially abundant in young larve, and occur in butterflies (Pierids and Satyrids), Geometrids (Ortholitha cervinata), Notodonts (Datana, Dasy- lophia), and many others. Packard describes the glandular hairs of newly-hatched larve of Ceratosia tricolor as ‘flattened at the tip, which is slightly tridentate, with grooves passing down the shaft from the notches between the teeth.” In the Pierids they form an open basin, fringed with cilia, supported on an exceedingly slender, hollow pedicel, the hairs looking as if tipped with dew. 3 In a preceding part of this chapter (p. 40), we query the absence of the paranal forks in the Rhopalocera. This is because Chapman has called attention to a well-known structure, called the ‘‘ anal comb,”’ which is possibly homologous with the paranal forks. It is found just under the anal flap in many Tortricid, Hesperid, and Pierid larve. Scudder figures the anal comb in Colias (Hurymus) philodice, but does not seem to mention it in the text. This should, of course, have been mentioned directly after the paragraph referring to the “ paranal forks.”’ It has been repeatedly noticed that certain larve, when confined, have a tendency to crawl upwards, and this is more particularly the case with some species than others. Larve of the genus Coleophora, Aglais urticae, Vanessa io and others, might be instanced as always taking possession of the highest possible point of any receptacle in which they may be placed. Poulton suggests that this is due to the fact that the larve in these movements are guided by an appreciation of the force of gravitation. That it is not always in order to seek food is evident, for the larvee will crawl over the food-plant in order to reach the highest available point. It is very possible that these movements are made in order to seek light, or air. At any rate, it is not yet at all clear how far the latter causes are factors in bring- ng about these movements, and how far the force of gravity has effect. Poulton further considers that the force of gravity has been potent in bringing about the characteristic ‘‘Sphinx-like” attitude that characterises the larve of certain Sphingids, Aglia, etc. This atti- tude, he says, bears a distinct relationship to the position assumed by these larve. The thoracic legs, in such larve as adopt this attitude, are not used for the support of the body, and, hence, when * “Studies in the Transformation of Moths of the Family Saturniidge,” Proc, Amer. Acad, Arts and Sciences, 1893. 52, BRITISH LEPIDOPTERA. the larva is clinging as is its wont, the weight of all the parts of the body anterior to the third abdominal segment is only indirectly supported by means of the claspers. He further points out that the young larve of all species which exhibit this habit, habitually rest on the underside of leaves, and, therefore, have the dorsal area pointing downwards. Under these circumstances ‘‘the organism reacts upon the strain, and the muscular body-walls strongly contract upon their fluid contents in such a manner as to produce compensating rigidity, and thus give to the body the curve which is characteristic of the attitude. The Sphinx-like attitude is to be explained as the com- bined effect of gravity and of muscular reaction upon the anterior un- supported parts of the body. The muscular arrangements, which are most favourable for counteracting these strains, are also made use of in the older larve for the maintenance of a feebly marked Sphinx-like attitude, when the larva is seated on the upper side of a horizontal twig. The attitude is most strongly marked when the larva is resting on a vertical twig, because gravity tends to draw the anterior part of the body backwards as well as downwards. ‘These large larve habitually rest on vertical twigs, with the head uppermost, because the twig itself is approached from its base, and gradually stripped of leaves towards its apex. The essential dependence of the attitude upon eravity is well seen, when a vertical twig, with a larva upon it, is carefully bent downwards, so that the strain is in the opposite direction, and tenas to bend the anterior part forwards instead of backwards. Under these circumstances the larva begins to yield to the strain in a few minutes (Trans. Ent. Soc. Lond., 1888, p. 675). An interesting subject of enquiry is the evolution of the Geometrid form. The fact that this form is found, in a more or less modified condition, in certain Noctuid larve, has suggested an alliance between the two groups. It seems very probable, however, that this similarity has been brought about by somewhat similar needs, the Geometrid form being, in many respects, a very specialised one. Many Noctuid larve that have the full number of prolegs when adult, are more or less Geometrid in form when young. It appears probable that this form has been developed in order to give these larve a greater reach (1) to obtain their food, (2) to travel from one twig to another. The Geometrids are essentially herbaceous and arboreal in their habits, remaining on their food-plants the whole of the day, so also are the Plusias and other Geometriform Noctuids. The Noctuids that have a Geometrid form of progression when young, also, at this period of their lives, remain on their food-plants, but when they gain the hitherto absent prolegs, they climb down the plants and hide at the roots, or under the ground by day, ascending the plant again to feed by night. The comparatively low-feeding Geometrid Jarve are, as a rule, small species, and the bushy herbs on which they feed, bear to their power of reach much the same proportion as the larger trees bear to the reaching power of the larger larve. Another view of the matter suggests itself, viz., the necessity of Geometrid larvee to travel more quickly than other tree-feeding larve. The Sphingids, Saturniids, Lasiocampids, Dicranurids, Catocalids, ete., are specially protected by spines, hairs, etc. The Geometrid larva is naked, usually only protected by the resemblance of its colour to its environment, and by its power to remain rigid and motionless, When THE EXTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 53 moving, therefore, it is helpless, and must travel from place to place with as much speed as may be possible. Livery observer knows that the tree-feeding larve of the other groups mentioned above are extremely slow in their movements. It is essential, above all things, that a tree-feeding larva should hold very firmly, and this it is enabled to do by spinning silken threads and ladders, and by the possession of remarkably strong and well-developed prolegs. The large Saturniids, arboreal Sphingids, Lasiocampids, etc., cling with amazing tenacity, but, at the same time, they walk with extreme slowness. With them, the opening and closing of their prolegs is a remarkably complex operation, in which a whole army of muscles is brought into play. The Geometrid larva has to cling as tightly as these. At the same time it has to move more rapidly, hence it has reduced its prolegs to the smallest possible effective number, and has, especially, anal ones of the very best kind. Thus it is able to obtain a long stretch for each step, and is able to progress with comparative speed. The young Noctuid larva, too, has often a considerable amount of travelling to do in search of food (eggs being often laid away from the food-plant, etc., ante, p. 18), and a certain amount of looping increases its activity by lengthening the step; and this is, perhaps, much more important in the young state when the larve have an arboreal habit. It may be, therefore, that rapidity and facility of progression is a great part of the object in view. An Arctiid larva, when travelling rapidly, hardly uses the prolegs at all, but progresses by a rapid looping movement, the ordinary progression, segment by segment, being altogether too slow for its needs. Hyery field naturalist has observed how a Geometrid larva will maintain its hold upon a twig and eat a leaf, and, for this, reach is also required. The difference between the way in which a tree- feeding Geometrid larva and a Sphingid larva will attack a leaf is remarkable. ‘The Geometrid stretches itself out to its full length, and eats as much as it can reach without moving, often beginning near the tip and devouring the whole leaf. The powerful Sphingid larva pulls the leaf towards itself, and thus does by greater strength what the Geometrid larva does by greater reach. The Geometrid form, therefore, appears to be correlated with habits of (1) greater reaching or stretching power, (2) greater speed. It does not seem to have any important phylogenetic significance. In a previous part of this chapter, we have referred to the fact that lepidopterous larvee have a certain number of ocelli on each cheek. Landois considers that these do not essentially differ from compound eyes, and states that if many of them were grouped together they could hardly be distinguished from compound eyes. In each ocellus, he says, the cornea is divided into three lenses, each corresponding to three nerves, each with a separate terminal enlargement, forming the so-called crystalline bodies. Each ocellus, therefore, might be re- garded as being, in reality, composed of three. On the other hand, the three arches of the cornea are so closely connected together, that they give the impression of forming a simple cornea. The three lenses are also very closely pressed, and the three nerves unite into one. Under these circumstances, Landois regards the ocelli of caterpillars as a connecting link between simple and compound eyes, and proposes for them the name of “ ocelli compositi.” Chapman says: That 54 BRITISH LEPIDOPTERA. the larval ocelli are descended from compound eyes, or are per- sistent from the embryonic form of compound eye, is undoubted. They often occupy a definite tract on the head, which probably repre- sents the area of the compound eye, of which some ocelli only are developed (in Jitt.). There has not, we believe, as yet, been any attempt to locate an organ of hearing in the larvee of Lepidoptera, although various authors have done so in the imago. Swinton summarises (Hut. Mo. May., x1y., p. 121) the various notes that have appeared on the aural apparatus of Lepidoptera. There is direct evidence that some larve, at least, show considerable sensitiveness to sound waves. We have noticed that larve of many species—Aglais urticae, Callimorpha dominula, Nemeophila plantaginis, and Lasiocampa querciis, among others—throw their bodies violently from side to side, if one speaks in a loud tone, when in their vicinity. CHAPTER VI. THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. Tuer external characters of the lepidopterous larva are, owing to the division of the body into segments, each with its own special organs and appendages, easily described, and the position of these structures located. The location of the internal organs is, however, more difficult, for they are not restricted to certain segments, but run longi- tudinally through the body, frequently extending from the thorax forward into the head, or backward into the abdomen. It is necessary, therefore, in dealing with the internal organs, to consider each separately, both as regards its position and function. The movements of the body are of the first importance, and we © find that larve have undergone great modifications in order to enable them to vary their movements according to their needs. Move- ment is dependent upon the muscular system, and by the muscles, then, the changes that take place in the external framework and appendages are brought about. The nutrition of the various parts is carried on by food, and to understand this we must study the digestive system. The absorption of the digested food into the blood and its carriage to all parts of the body necessitate a circulatory system, whilst the oxygenation of the blood introduces us to the respiratory system. This latter is so intimately connected with the excretion of waste, that one is insensibly led to consider the excretory system, whilst the organs, by which the whole of these various systems are governed, comprise what is known as the nervous system, and this has to be considered both in its relation to volition and sensation. ; These various systems comprise, then, the different organs (and their functions), by means of which the life of an insect is carried on, and their external results, as exemplified by their movements, etc., are the outward sign of their vitality. The reproductive system, which is not, however, matured in the larval stage, must take the highest place in relation to the continued life of the species. Closely related, THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 55 too, with the digestive, is the cellular, system, by means of which the caterpillar is able to store up large quantities of surplus material for use in the later stages of its metamorphoses. The voluntary muscular system of the caterpillar is that by means of which it is enabled to move about in order to obtain its food. The muscular fibres are usually arranged in the form of flat ribbons, or conical bundles. The latter make up almost the whole structure of the head, are fastened chiefly to the head walls, and end as fine tendinous cords, attached to the various organs which the insect is thus enabled to move. In this way, certain muscles reach down into the mandibles, which they close when they contract; whilst the mandibles are opened by muscles which are attached to their outer bases and to the head, just below the ocelli. Other fine flat retractor muscles draw the labrum inwards, whilst extensor muscles work in the opposite direction. A series of contiguous muscular cords, often forming a double band of simple, longitudinal muscular fibres, runs from one end of the body to the other, on each side, just under the skin, between the spiracles and the ventral area of the body. Mus- cular bands, too, run transversely and obliquely in the front of each seg- ment, and are attached to the medio-ventral line farther back in the segment. Above the spiracles on each side are other longitudinal bands, made of three layers, whilst between these and the skin, at the front of each segment, a transverse muscular belt encircles the body, passing at the spiracular region over the longitudinal tracheal vessel, which unites the contiguous spiracles, and straps it to the integument. The flexor muscles of the true legs arise just beneath the longitudinal straps, previously described as running between the spiracles and the ventral area, and extend to the opposite wall of the segment in which they take their rise. The muscles of the prolegs are somewhat different, flat bands forming, as it were, a muscular coating to the walls of the legs just beneath the skin. Usually, these pass directly down, narrow- ing as they go; the muscular fibres, too, appear not to cross to opposite sides of the leg. The involuntary muscular system is principally connected with the digestive and the circulatory organs. The cesophagus is provided with fine longitudinal bands of muscular fibres, and also with less well- developed transverse encircling bands. The inner coating of the stomach is enclosed in delicate strips of muscular fibre, crossing each other diagonally; besides these, longitudinal muscles run throughout its length, and well-developed transverse muscles encircle the stomach similarly to those found in the esophagus. The arrangement of the muscular tissue in the intestine, in longitudinal and transverse bands, is very similar to that in the other parts of the alimentary canal, but, in this, the longitudinal bands are often thick, white and glistening, whilst near where the small intestine joins the stomach, the walls are plentifully supplied with short longitudinal muscles. The diagonal bands found in the stomach have also their representatives here. The alimentary canal is held in its place by a series of muscular bands attached to the body wall, one set passing round that portion of - the intestine where it is connected with the stomach, another set being attached to, and supporting, the posterior end of the small intestine, these muscles stretching horizontally from the middle of one side of the 8th abdominal segment to the opposite side. 56 BRITISH LEPIDOPTERA. The mouth opens into a long narrow tube (the csophagus), into which several long tubules pass. These represent the salivary glands of the higher animals, and secrete a fluid, which is discharged into the cesophagus, and which is swallowed with the food. It dissolves the starch and cellulose of the food, and fits it to soak through the walls of the alimentary canal, so that it can enter the system. The ceso- phagus is composed essentially of muscular tissue, and expands into a crop (or food receptacle), and then into a gizzard. This is provided with hard plates, that help to grind up the food, which, after being so ground up, is passed through another short tubular passage into the stomach. The walls of the stomach secrete a fluid resembling the gastric juice of the higher animals; this changes the insoluble proteid of the food into a soluble peptone, which is readily absorbed by the walls of the stomach and intestine. The stomach opens into the intestine, the upper end of which is connected with a number of tubular glands. These are supposed to represent the liver of the higher animals. The intestine ends in a chamber called the ‘‘ cloaca,” in which the waste matters are collected, and from which they are expelled through the anus. In vertebrates, the nervous system is placed dorsally, and the circulatory and respiratory systems ventrally, in relation to the ali- mentary canal. These positions are exactly reversed in insects, the nervous system being placed ventrally, the circulatory and respiratory systems dorsally, the alimentary canal being still placed between them. It has, however, been shown that this difference is more apparent than real, the dorsum of the insect being really analogous with the venter of the vertebrate, but the position of the limbs is reversed. In the upper part of the body, and directly under the dorsal integument, is a longitudinal organ, somewhat like a long tube, which is known as the dorsal vessel. This corresponds with the heart of the vertebrates, and it consists essentially of only one chamber, although this is divided into 8 or 9 sacs, the latter, with openings along the sides, called ostia. It is composed chiefly of muscular tissue, and is connected with the roof of the body by short stout muscles, which keep it in position. It opens towards the head into a kind of arterial trunk. As the dorsal vessel contracts from behind forwards, the blood, which consists of plasma, or fluid, and colourless corpuscles, is driven forward into the trunk. The latter subdivides into smaller vessels, which are soon lost, the walls gradually becoming inseparable from those of the ordinary lacune, or depressions found between the tissues, and which are lined in many places with epithelium. As the blood passes through these lacune, it is brought into contact with the tracheal branches and aerated. At the same time the nutritious parts of the food, which soak through the walls of the stomach and intestine, enter the blood in the lacunz found near these organs. The great difference that exists between the blood of insects and that of vertebrates, is such that one feels that it is a great mistake to call two so dissimilar fluids, with different functions, by the same name. The blood of insects varies with the species, sometimes even with the various stages of the same insect. Its function is to carry the nutritious matters to the tissues, and to feed, as it were, the tissues it bathes. It is frequently filled with somewhat crude fatty matters, and Graber calls it ‘‘a refined or distilled chyle.”’ THE INTERNAL STRUCTURE OF THE LEPIDOPTHROUS LARVA. 57 Beneath the dorsal vessel, a fine membrane is stretched in such a manner as to separate the dorsal vessel from the surrounding organs, and, at the same time, leave a cavity around the dorsal vessel itself. This cavity is called the pericardial cavity or sinus. The membrane itself is incomplete, and when certain delicate muscles connecting it with the body-wall contract, they pull 1t down tightly upon the tissues below, and this, of course, at once increases the size of the sinus. The tissues thus pressed upon are full of chyle and blood, and the fluid is squeezed from these structures through the incomplete mem- brane, into the pericardial chamber, and from thence it re-enters the dorsal vessel again. The number of contractions of the dorsal vessel varies remarkably. They may amount to as many as a hundred per minute; they may cease altogether without death ensuing. It is recorded as pulsating from 48 to 52 times per minute in the larva of Triaena (Acronycta) psi, and 44 times per minute in the larva of Brotolomia meticulosa. In spite of the fact that Swammerdam, Réaumur, Bonnet, De Geer, and others, all speak of blood-currents, of fluids moving in the body, of pulsations of the heart or dorsal vessel, and of circulation, Kirby and Spence record their emphatic opinion that there is no circu- lation in insects. The idea of circulation taking place in the lacunze of the tissues does not appear to have suggested itself, and the early authors appear to have thought that definite tubes with definable parietes were necessary for circulation. Bowerbank, and others, placed the matter beyond dispute, and it is only necessary to refer to it here, because many entomologists still seem inclined to accept the state- ment of Kirby and Spence. The fat-body is a very prominent part of the structure of the lepi- dopterous larva. It consists of fat masses of various size, loosely connected together, and enveloping most of the organs. It varies in colour and appearance in almost every species of insect, and appears to consist of a reservoir of reserve material, which increases in the larval stage, when the insect is busily engaged in feeding, and upon which the insect can draw in the future, when it is unable for along period to take food, e.g., such periods as occur at each exuviation of the larval skin, and also at the more exhausting periods of metamorphosis. It must also be looked upon as a storehouse on which the insect can draw when in the more quiescent pupal stage. The respiration of the Lepidoptera has been partly dealt with in the preceding chapter, and we have seen that air is conveyed into all parts of the body by means of the trachea. The trachee are elastic tubes, held open by an inner chitinous layer, and they are all intimately connected. Large tubes connect the spiracles longitudinally, others pass from one side of the body to the other, whilst a set of trachez in the lower part of the body is connected with another set in the upper part by ascending tubes. ‘These main branches give out small branches, which fork in all directions, and hence the body is supplied most plenteously with air. The tubes have a white glistening appearance, and hence can be detected in a freshly killed Insect without difficulty. [In insects of strong flight, there are air-sacs connected with the trachez, and capable of holding sufficient air to decrease, when distended, the specific gravity of the insect.] The finest tracheal tubes are supposed to penetrate cells, but it is not known whether they terminate with open or closed extremities. 58 BRITISH LEPIDOPTERA. The activity of the respiratory system of the Lepidoptera may be readily surmised from the rapidity with which they are affected by agents, such as ammonia or chloroform, yet the exact manner in which breathing is carried on is unknown. Rapid movements of contraction and expansion of various parts of the body, accompanied by the opening and shutting of the spiracles, are often observed, and are supposed to be respiratory, but it is generally believed that, al- though the trachee must supply the tissues with oxygen, they do not carry off the carbonaceous waste from the tissues. Many consider that some of these waste matters are passed from the skin, and this is more probable than any other explanation yet offered. It is well-known that caterpillars, shut up and with insufficient air, throw off waste products most freely.from the skin, the process being popularly known as ‘‘sweating.”” Some entomologists consider that the skin is built up from within, and since chitin is composed largely of carbon and nitrogen, it is possible that certain of the waste matters may be used in the formation of chitin, and finally passed off when the larva exuviates or casts its skin. The Malpighian tubes, a number of coiled filaments found in the dorsum of the larva, used to be considered analogous with the liver of vertebrates, and were supposed to secrete a substance somewhat analogous with bile. They are now known to be excretory organs, and to remove various compounds from the system. It is not yet known how the tubes are emptied, but the material contained in those of some of the Lasiocampid and Saturniid moths, is supposed to be mixed with the silk of the cocoon, and to be used for the purpose of hardening the latter. It certainly seems to be so used in Malacosoma (Clisiocampa), Evriogaster, etc. The substance excreted is generally in the form of oxalate of lime, or some allied compound. Lepidoptera, in common with many other insects, have a very complicated nervous system, which may be conveniently considered as consisting of three divisions: (1) The cephalic system. (2) The ventral or ganglionic chain. (8) The accessory sympathetic system. These divisions are, of course, very intimately connected. The cephalic system consists of two masses. One is large, and placed above the cesophagus, and, hence, is termed the supra- cesophageal ganglion; the other is smaller, and placed below the cesophagus, and, hence, is termed the infra-cesophageal ganglion. These are united with nerve fibres, passing round the cesophagus, and forming what is often termed the cesophageal ring or collar. These cephalic ganglia are often spoken of as the brain, and, in these, the nerves which supply the eyes, antenne and tongue originate. The ventral chain consists of a series of ganglia. ‘These are small masses of nerve substance, placed longitudinally along the ventral side of the insect. They are arranged in pairs (theoretically one pair in each segment, although often various pairs of ganglia are united), and the ganglia are connected with the ganglia preceding and suc- ceeding by longitudinal nerve fibres or commissures. From these ganglia the motor nerves of the body are distributed to the muscles in the various parts of the body. In the larva of Tischeria angustico- lella, the paired ganglia are very distinct in each of the thoracic seg- ments, and in the abdominal segments 1-6. Scudder says that they are usually found in the lepidopterous larve as far ag the 7th ab- THE INTERNAL STRUCTURE OF THE LEPIDOPTEROUS LARVA. 59 dominal segment, in which there is a pair of ganglia, and here the neryous cord terminates. The nerve ganglia of Tischeria are placed -very nearly to the front of each segment. [In the lepidopterous imago the union of the ganglia in adjacent segments is sometimes very com- plete. In different families there appear to be sometimes two, at other times three, thoracic ganglia, but always four abdominal ganglia, with the exception of the Hepialids, which appear only to have three. | The sympathetic system consists of a median nerve cord, dilating at intervals into ganglia, and placed above the ventral system, with the commissures of which it is connected by nerve fibres. The nerves from this system are distributed to the various organs of the body connected with alimentation, circulation and respiration. It must be remembered that, although apparently so different, the development of the nervous system in the embryo is analogous with that in vertebrates, and that, although the nervous system of insects is apparently ventral, whilst that of vertebrates is dorsal, the ventral part of an insect corresponds with the dorsal part of a vertebrate, 7.e., in reality, opposite parts of the body are placed ventrally in insects and vertebrates respectively, owing to the limbs being turned in opposite directions in the two cases. It used to be a generally accepted belief that the lepidopterous larva had no sexual organs, and this, in spite of the fact that Réaumur, a century and a half ago, stated that he had discovered eggs in the larva of Porthetria dispar, and that Malpighius found them in the larva of Bombyx mori. The reproductive organs, however, are not difficult to observe in some larvee, and can usually be obtained by a little careful dissection. ‘The testes and ovaries are placed just beneath the skin of the 5th abdominal segment. They exist in pairs, one on either side of the dorsal vessel, just above the position of the alimentary canal. The testes form two lobes of a not very distinctly reniform shape, whilst the ovaries, which are only to be seen with a lens, and then in comparatively few species, are much smaller, and consist of tubes. The testes are generally much more readily observed than the ovaries, being, usually, yellow or brown, and may be seen distinctly in the larve of those species which feed internally, or which have fairly transparent skins. Weniger detected the blind terminations of the ducts from the sexual organs in the larve of Antheraea yama-mai, A. pernyt, Actias selene and Samia cecropia, ‘‘ on the underside of the last segment that bears a spiracle’’ (Sth abdominal). In the female of the first of these species is a black blotch, with a yellow central spot, whilst in the male is a similar black blotch, with a dark green central spot. Herold represented, as long ago as 1815, the changes which the essential reproductive glands undergo in the larva and succeeding stages of Pieris brassicae, but up to the present time there appears to have been no external openings, in connection with the sexual organs, discovered in any lepidopterous larva. Certain statements which have been made on this subject are mentioned here only in order to draw attention to them, in the hope that they will be disproved or confirmed. De Geer states that the brown larve of Triphaena pronuba produce males, and the green larve, females. Doncaster says that the same larval colour distinction, as to sex, holds good in the Satyrid butterflies. _ Healso states that the male larve of Orgyia antiqua and O. gonostigma have yellow dorsal brushes, the female larve, brown. Suckow distin- 60 BRITISH LEPIDOPTERA. guishes male Dendrolimus pint larvee from female larve: (1) By the smaller size. (2) By the lighter, almost smoky-grey colour. (3) By a black-brown band situated beneath the second pair of prolegs. {This band is said to be only obscurely marked in the female). Jackson says that the larval ovaries are situated in the 5th abdo- minal somite, and close to the dorsal middle line. Their proximal or attached extremities are approximated, and they diverge from one another posteriorly. The colour gets deeper during the quiescent period preceding pupation. Four opaque white lines, the future ovari- oles, traverse the larval ovaries lengthwise and converge towards their hinder extremities, from which the larval oviducts spring. The latter are very delicate filaments, and difficult to make out. Bessels gives the following table of species in which the larval testes and ovaries are dissimilar in colour :— SPECIES. Ovary. TESTIS. Fat-Bopy. - Porthetria dispar ... yellow 006 flesh-red 900 white Cosmotriche potatoria yellow ie yellow wes white Deilephila euphorbiae yellow ae reddish 206 yellow Pieris brassicae 400 yellow 000 violet aes white Cossus ligniperda ... white 900 white aac white Jackson adds that, in these particulars, the larve of Sphina ligustri and Phalera bucephala agree with Cossus. In Pieris brassicae the fresh fat-body posteriorly to the 6th segment is greenish or olive-yellow, anteriorly to it opaque yellow or green on the dorsal aspect, but on the ventral aspect white. ‘The fat-body of the larva of Vanessa io is yellow, and becomes orange in the pupa (Trans. Linn. Soc. Lond., Zool., vol. v., p. 159). With regard to the point of development reached by the sexual organs in the lepidopterous larva, it would appear that they have developed as far as that reached by the adult (imago) Ephemerid (May- flies). Inthe imagines of the Lepidoptera, the two oviducts unite, and form a single tube down which the egg passes. In the adult Ephemerid, the two oviducts remain separate. In the larva of Vanessa io, the oviducts are separate, as in the Hphemerid imago, but by the time that the butterfly is matured, the oviducts have united to form a quite typical ovipositor. Such a line of evolution, however, suggests that the oviduct. of the Lepidoptera passed through a stage similar to that which is to ‘be observed in the Hphemera at the present time, before it reached its present high stage of development. CHAPTER VII. THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. Tur variation in the colours of insects is so patent to every observer of these interesting creatures, that there is no need for cne to attempt to show that variation exists. Superficially examined, we find that the individuals of a given species are very similar to each other, yet the eye of an expert sees minute differences in these individuals, and he knows that just as no two men or women are exactly alike, so no two THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 61 insects are, in any of their stages, precisely similar. Variation is general throughout every stage of an insect’s existence, 7.c., in the egg, larval, pupal and imaginal stages. Every living animal seems to exist for two distinct purposes—to eat and to be eaten. Nature provides everything with a means of offence or defence, or both. Among insects, weapons of offence are rare, and, generally speaking, their safety lies rather in their defensive characters. ‘These are usually of the most inactive kind, and consist essentially of various disguises, by means of which, when in repose, they bear a strong resemblance to the various objects on which they rest—the bringing into harmony, as it were, the colours of insects with their environment, so that they may agree in tint with the object on which they rest, or that they may bear a close resemblance in hue and shape to some object common upon their resting-place. ‘This bringing into harmony presupposes the possibility of a change in the colours of insects, in order that they may respond to the varying con- ditions under which they may be placed, and in which they have to live. This further presupposes a plastic condition of the colours them- selves, otherwise they would not be able to respond to differences of environment. These differences are so many and so varied, that we find variation in the colours of insects occurring under a multitude of different conditions, and to be presented in a variety of ways. In these notes we shall confine ourselves to the brief consideration of a few of the principal phases of variation exhibited by the imagines of certain Lepidoptera. The colours of the wings of butterflies and moths are due largely to the scales found on the wing membrane, and, in a less degree, to the colours of the wing membrane itself. The scales themselves are hollow chitinous cells, united by a ball and socket joint to the mem- brane of the wing. They are epithelial expansions, which, having attained the size and shape peculiar to the species, become hardened externally by a chitinous deposit. In the process of their develop- ment, they go through a regular series of changes. They are at first transparent, then they become whitish, then a secretion from the pupal hemolymph, called ‘‘ pigment factor,” enters the scale, and it becomes yellow; lastly the pigment-factor is elaborated, and the scales assume the coloration that they will have in the wing of the perfect insect. These changes, of course, all take place in the pupa, before the imago emerges, and no development takes places afterwards; any change that then occurs being due to exposure, the influence of light, ete. There can be no active response, whatever, in the perfect lepidopterous insect, to any change of environment, é.e., no change can occur in its colora- tion once the insect has emerged from the pupal state. Ordinary white light can be decomposed. Popularly, we say, it can be broken up into a number of differently coloured lights—red, orange, yellow, green, blue, indigo and violet, and we call these the colours of the solar spectrum. ‘These colours, in fact, represent the effect produced on the optic nerve by the variable rate of vibration of the constituent waves, of which white light is really composed. If a substance has the power of absorbing some of the light waves, from the white light which ordinarily falls upon it, and of reflecting others, only the reflected portion can possibly affect the optic nerve. If the red rays only be reflected, then the colour of the substance appears to 62 BRITISH LEPIDOPTERA. us to be red, if blue, then the colour appears to be blue, and so on. Substances which are thus able to select certain light waves for absorption, and to reflect others to our eyes, are termed pigments, and the fact that most scales of Lepidoptera contain substances that can do this, causes us to term the colours thus produced pigmentary colours. But colours are also obtained by the refraction, interference and diffraction of white light. Scratched and striated surfaces diffract light. Diffraction breaks up the bent part of a ray of light into its component parts, and, dispersing the waves, gives, on the edge of each bright space between the slits or striations, a fringe of colour. The exposed surface of the scales of many Lepidoptera : are striated, both longitudinally and transversely, hence these produce surface colours by diffraction. One of the best-known examples of this kind of coloration in British insects is the purple of the male of Apatura aris. Such colours as these are usually termed in entomological magazines, non-pigmentary colours. Having thus briefly stated the phenomena by means of which, practically, all the colours of the scales of butterflies and moths are derived, we see that the colours are due either to the selective power of the pigment contained in the scales or membrane of the wing, or they are due to the peculiarities of structure and form of the scale. We have already stated that variation is general in all insects, no two butterflies or moths of the same species being exactly alike. Sometimes this general variation in a particular species is so marked and conspicuous, that the most casual observer notices the fact. Such species are then said to be polymorphic. In a less degree, however, it may be accepted as a general fact that all species of insects are polymorphic. The enemies of butterflies and moths are very numerous—insec- tivorous birds, reptiles, mammals, other insects—and as they have practically no weapons of offence, their safety lies in their resemblance to their surroundings. Danger, to them, is probably more real when they are at rest, hence, when at rest in a natural attitude, one is at once struck by the marvellous resemblance which most butterflies and moths bear to the surface (or to some common object on the sur- face) on which they rest. With the initial general variation which we have observed to occur in all insects, it is pretty certain that some individuals will be more readily detected than others, some peculiarity of tint, some mark or spot of colour, maybe, rendering them a little more conspicuous. ‘These will fall a more ready prey to the enemies that are searching for them, and they are, as a rule, the first eaten. Those that are best protected are most likely to be left, the laws of heredity step in, and a larger proportion of well-protected specimens results in the progeny. Of course, the general variation which must exist in all broods, and between all individuals, the tendency to atavism, and similar causes, will always result, even then, in producing some less favoured individuals. Still the ceneral result will be that a well protected race, suited to the particular environment by which it is surrounded, will be developed. It is evident, when we consider the different habits of insects, that the particular habit and environment of each species, will determine THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 63 the main general lines on which the variation of the species will proceed. Butterflies sit with closed wings, hence it is the undersides of butterflies that are then exposed, and, therefore, the undersides take such form, colour and markings, under the influence of natural selection, as will best protect the individual, ¢.g., the marbled green and white underside of Huchloé cardamines, which rests on umbelli- ferous flowers, the dark undersides and jagged wing margins of the Vanessids, which hybernate in hollow trees, and exactly resemble dead leaves, when at rest. Then there are the ‘‘reed’’ moths, which, be- longing to many different super-families—Nocrumss, Liparipes, Cram- BipEs, Tortricipes, Tinemes, ZEuzERIDES—sit by day on the reeds, their bodies closely appressed to the reed, their wings folded partly round it, so that each insect represents a gentle swelling of the stem, culminating in an apparent node on the culm, where the insect’s head is situated. The colour of all these moths is a very pale wainscot— the tint of a dead or dying reed—with very fine longitudinal striations, agreeing absolutely with the colours and markings of the reed stem. Another large group of moths—chiefly GrometrmEs—have the habit of resting on tree-trunks, where their general grey hue, marbled with transverse wavy lines, gives them a very close resemblance to the bark on which they rest. Again, in hilly and mountainous districts particularly, a large number of species rest upon the rocks, when their colour usually assimilates closely to that of the rocks upon which they rest, and these, too, are generally covered with transverse wavy lines, which cause them to be very inconspicuous so long as they remain immovable upon their resting-places. Some moths that rest on walls, rocks, or trees, are marked with green and yellow. Such are the species of Polia, Bryophila and Cleora, Larentia flavicinctata, and others. These, when at rest, are scarcely to be distinguished from the lichens which grow upon the rocks on which they sit. Then there are the green and yellow moths—the Emeralds, Thorns and Sallows—which hide among the leaves of trees, or the lower herbage, and resemble, in hue, dead or living leaves so exactly, that they are scarcely to be detected, whilst those that rest among the roots of grass and low her- bage, generally, are of various shades of grey, or buff, or brown, which make them very inconspicuous near or upon the surface of the ground. It is quite clear that, in all these general cases, and in many special ones, natural selection has produced races, particularly well suited in the case of each species to the environment in which it is placed, also that the more conspicuous individuals become a ready prey to enemies, whilst inconspicuous individuals are more often left to carry on the race. One of the most interesting special phases of variation exhibited by British Lepidoptera is that of melanism and melanochroism, the former term being applied to those individuals which exhibit a tendency to develop a greater proportion of black in the ground colour than is exhibited by the type, the latter, when the ground colour is intensified, but not in the direction of becoming blacker. The ab. doubledayaria (popularly known as the ‘‘Negro”’) of Amphidasys betularia may be cited as an example of the melanic class. The ab. ochracea (of a deep ochreous or buff tint) of Spilosoma menthastri, which is white in its typical form, is a very good example of those insects which exhibit melanochroic tendencies. These tendencies are noticed to be much 64 BRITISH LEPIDOPTERA. more generally developed in species that rest on fences, the trunks of trees, the faces of rocks, or on the ground, than in other species. It may, of course, be assumed that those usually found upon fences were originally confined, more or less, to tree-trunks, and that the influences acting upon one are equally potent on the other. It has been observed that, in a great number of species of moths that rest on fences and tree-trunks, and are more or less abundant in the London district, the individuals are darker in colour than those of the same species, captured a few miles outside the metropolis. This is clearly observable in Triaena pst, Hemerophila abruptaria, Acidalia virgularia, Kupithecia rectangulata, Melanippe fluctuata, Boarmia gem- maria, Hybernia defoliaria, H. marginaria, H. leucophaearia, Oporabia dilutata, Diuurnaea fagella, Tortrix podana, Hedya ocellana and many other species. There can be no doubt that in the suburbs of London, fences and tree-trunks are generously covered with soot. (Those who have green- houses, and attempt to keep the white paint clean, will understand how completely they are covered). The tree-trunks have become darker during the last fifty years, and the depth of colour is gradually increas- ing in what were then suburban districts. The pale grey and ochreous specimens of the insects just named used to be well protected on their then clean resting-places. Such specimens are now exceedingly con- spicuous when they occur, which they only occasionally do, for the selec- tion of the darker specimens for preservation by nature, has resulted in the permanent darkening of the race. But itis in the manufacturing districts—in Yorkshire, Lancashire, Cheshire, Derbyshire, Notts, Staf- fordshire, South Wales, ete.—where thick smoke is poured from number- less chimneys, and where the fences, tree-trunks, and even the surface of the ground are begrimed with soot, that the most marked cases of what may be termed protective melanism occur. ‘There we get the “Negro” aberration (ab. doubledayaria) of Amphidasys betularia, the ab. niyra of Tephrosia crepuscularia (biundularia), the ab. fuscata of Hybernia marginaria, the ab. obscura of Kpunda viminalis, the ab. nigra of Boarmia repandata, whilst many other species give absolutely black aberrations, which are rarely observed elsewhere. These black aberra- tions, it is well-known, have practically come into existence during the last half-century, and their range is rapidly extending. So completely, too, are many of these dark aberrations supplanting the type that, in some localities, the pale typical forms are almost unknown. These moths are nearly all essentially grey—that is, black and white—in their typical forms. The gradual darkening of the tree-trunks, etc., by the deposition of soot, has resulted in the better protection of the darker specimens, and hence their better preservation, and, as we have just hinted, the trunks and fences have become so blackened that, in some - districts, the absolutely black specimens comprise the best protected form of the species. Parallel, if not absolutely identical, with this form of melanism is that exhibited by those species that rest on rocks. Certain Alpine species exhibit this form of melanism inamost marked manner, both in the mountains of EKurope and N. America. Certain species that rest on peat are black, wherever they may be found, and however different may be the meteorological conditions of the various districts they inhabit. On the peat bogs in the New Forest, Gnophos obscurata THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 65 is black, so also is it on the dark rocks of Perthshire; in Sussex, on the chalk, it is white, and the response of this moth, in ground colour, to the colour of the rocks on which it rests, is very remarkable. The black specimens found on peat in the New Forest, and on the dark rocks of Perthshire, have a similar melanic appearance, the colour evidently having been induced under such entirely different environments, by a similar process of selection. But it is in the wet, mountainous, and western districts of the British Islands, where the rocks are blackened with moisture, and, even in summer, do not lose one lot of wet until they have received another, that we find the most striking cases of melanism. Thus, on the coasts of Scotland, the Isle of Man and Ireland, we find black races of Agrotis lucernea, an insect that is quite pale on the chalk rocks of the Isle of Wight. In the Isle of Man the dark ab. manani of Dianthoecia caesia, quite unlike the mottled Continental type, occurs. The aberrations nigra and in- fuscata of Xylophasta monoglypha, an insect which rests upon the ground, are found in all districts where the rocks are naturally dark, or where there is a heavy rainfall. On the west coast of Ireland, melanic forms of Camptogramma bilineata are found resting on the rocks, and contrasting greatly with the beautiful golden specimens that hide on the undersurfaces of leaves in our gardens, whilst the aberrations sufusa, intermedia, ochrea and obliterae of Dianthoecia conspersa are found on our northern and western coasts, and respond so perfectly to the rocks upon which they rest, that the professional collectors can tell almost the exact localities in various parts of the Shetlands and Hebrides, from which individual specimens have come. In Shetland, again, the little whitish Hmmelesia albulata of our southern pastures and meadows, becomes of a deep unicolorous leaden colour. In all these cases, moisture plays an important, if indirect, part. In the first case, it brings down, in manufacturing districts, the soot in the air, which, when evaporation takes place, is left behind and forms a coating on the tree-trunks, fences, or rocks on which the insects hide. In the second, it permanently darkens the rocks in mountainous districts, and more or less so in the western areas, where there is a heavy rainfall. It makes, therefore, the work of natural selection in the direction of producing melanic aberrations exceedingly easy. This aspect of melanism has been already worked out at con- siderable length.* There have been occasionally general statements made to the effect that insects from high latitudes are usually melanic. This is so, if only the coast districts and areas with a heavy rainfall be taken into account ; but if the open areas of high latitudes be considered, we find that, although there is a general suffusion of markings and a tendency to ill- developed pigment, due probably to the extreme conditions under which development takes place, yet, as a rule, melanism israre. Mr. Merrifield has, however, shown us two cases in which temperature tends to pro- duce melanic forms. These are remarkable from the fact that the exposure of the pupa to a low temperature in one case, L'uyonia poly- chloros, produces a melanic form; in the other, Chrysophanus phlaeas, exposure of the pupa to a high temperature produces a somewhat similar result. These, and parallel cases, are not difficult of explanation. * Tutt, Melanism and Melanochroism in British Lepidoptera, 1891. ‘ E 66 BRITISH LEPIDOPTERA. The pupe are exposed to the low and high temperature respectively, at the period when the scale-pigments are undergoing differentiation in the scales, from the hemolymph of the pupal blood. There is a point at which this elaboration is carried on at a normally healthy rate. At a temperature considerably above or below this normal point, the pigment is developed abnormally, maybe never reaches its normal condition (chemically), or, maybe, overshoots it. In either case, abnormal conditions are produced, and, in these two instances, the abnormality results in a melanic appearance of the insects. There are, of course, other forms of melanism which probably have nothing in common with the cases already cited. One of these is well represented by the ab. valesina of Dryas paphia, by the ab. suffusa of Argynnis aglaia, etc., which are probably survivals of the old form of the Argynnid female (vide, Hntom. Fec., i., pp. 29-31). The production of albinism in Lepidoptera is not of very frequent occurrence, still it occurs sufficiently often for the phenomenon to be worthy of mention. It occursin a more or less perfect manner in species that rest on the ground, and which vary in tint according to the colour of the soil upon which they rest. In Gnophos obscurata, almost purely white specimens are often found in districts where the insects rest upon the bare chalk, and the same is true of Hubolia bt- punctaria, which has almost similar habits. These insects are, in their typical forms, grey, z.e., their scales are—some black, others white. The process of natural selection has weeded out the more conspicuous (darker) examples in these localities, until a more or less white race has been produced. It may be urged that these are nottruly albinic specimens, but they are exactly parallel in their mode of development with some of the melanic forms to which we have previously referred. True albinic specimens, we take it, are such as those of Calli- morpha hera, Triphaena pronuba, Catocala nupta, and other species that have been recorded, in which the yellow or red pigment has failed, and the scales have become white. In dealing with these specimens it is evident we have a result based directly on physiological processes, for the scales contain no pigment, the normal elaboration of the hemolymph ma- terial having been largely or entirely suspended and the scales filled with air. In our collection are specimens of Hemerophila abruptaria © and Hybernia aurantiaria exhibiting this phenomenon, and we believe that the specimens of Sesia culiciformis in which the normal red (or yellow) pigment of the abdominal belt is occasionally white, afford a similar instance. Not very different is the cause which gives rise to the xanthic aberra- tions, which are often included under the same head. In a paper, ‘