pili 10 ALISYIA AWN ADOIOOZ Digitized by the Internet Archive in 2010 with funding from University of Toronto http://www.archive.org/details/entomologywit0Ofols vi ht. if x } vn ‘ f ' { i ‘ . 1 L ¥ i M 4 z 4 i) i * 1 ft Yad) F 1 Ji ENTOMOLOGY FOLSOM hte py - DESCRIPTION OF FRONTISPIECE. ProtectiIvE Mimicry AMONG BUTTERFLIES. Fic. 1.—Heliconius eucrate, one of the Heliconiine, which are naturally immune from the attacks of birds. From Brazil. Fic. 2.—Perhybris pyrrha, female (Pierine), which is edible by birds but probably secures immunity by means of its resemblance to such species as No. 1 or No. 4. Brazil. Fic. 3.—Perhybris pyrrha, male, to show the colorational basis from which the mimetic pattern of the female has been developed; under surface on right. Brazil. Fic. 4.—Mechanitis lysimnia (Ithomiine), naturally immune, but nevertheless sharing a common color pattern with Heliconiine (No. 1). Brazil. Fic. 5.—Papilio merope, male, having three forms of females (Nos. 7, 9 and 11), which mimic, respectively, three species of Danaine (Nos. 6, 8 and 10). South Africa. Fic. 6.—Danais chrysippus, immune, mimicked by No. 7. South Africa. Fic. 7.—Papilio, merope, female, which mimics No. 6. South Africa. Fic. 8.—Amauris niavius, “ model” of No. 9. South Africa. Fic. 9.—Papilio merope, female, “ mimic ” of No. 8. South Africa. Fic. 10.—Amauris echeria, “‘ model”? of No. 11. South Africa. Fic. 11.—Papilio merope, female, “‘ mimic” of No. 10. South Africa. The figures are about one half the natural size. Compiled, largely from Trimen and Weismann. me i aldifie at: Wile (aera Fusiogge sone ot oigerstdrit329% ati: ‘Yo 208 Meresd {snottsrolos sit worle ot olsme mo sostiue tobe ~beqoleveh tocd esd ol | actrcetat yllstirteit (ostritin oT) ont fisex€ (2 10) sertin , pov) asleerst io errroi: ts 2 0 20%) semtsanG ‘points. dtioe: os Sort See BN TOMOLOGY WITH SPECIAL REFERENCE TO BS eelOLOGiICAL AND ECONOMIC ASPECTS BY 2e cf. (Stes WATSON FOLSOM, Sc.D: (Harvar) INSTRUCTOR IN ENTOMOLOGY AT THE UNIVERSITY OF ILLINGIS ee Sry With Five Plates (One Colored) and 300 Tert=FFigures By aC iS RS PHILADELPHIA : / a? eee Opera oad OUN Se SON: -& cae o oy 1012 WALNUT STREET ar nd \ ay 1906 as ee? ow COPYRIGHT, 1906, BY P. BLAKISTON’s Son & Co. PRESS OF THE New ERA PRINTING COMPANY LANCASTER, PA PREFACE This book gives a comprehensive and concise account of insects. Though planned primarily for the student, it is in- tended also for the general reader. The book was written in an effort to meet the growing demand for a biological treatment of entomology. The existence of several excellent works on the classification of insects (notably Comstock’s Manual, Kellogg’s American Insects and Sharp’s Insects) has enabled the author to omit the multitudinous details of classification and to introduce much material that hitherto has not appeared in text-books. As a tule, only the commonest kinds of insects are referred to in the text, in order that the reader may easily use the text as a guide to personal observation. All the illustrations have been prepared by the author, and such as have been copied from other works are duly credited. To Dr. S. A. Forbes the author is especially indebted for the use of literature, specimens and drawings belonging to the Illinois State Laboratory of Natural History. Permission to copy several poe from Government publications was received from Dr. . O. Howard, Chief of the Bureau of Entomology; Dr. C. aA Merriam, Chief of the Division of Biological Survey, and Dr. Charles D. Walcott, Director of the U. S. Geological Survey. Several desired books were obtained from F. M. Webster, of the Bureau of Entomology. Acknowledgments for the use of figures are due also to Dr. E. P. Felt, State Entomologist of New York; Dr. Eas Birge, Director of the Wisconsin Geological and Natural His- tory Survey; Prof. E. L. Mark and Prof. Roland Thaxter, of Harvard University; Prof. J. H. Comstock of Cornell Uni- versity; Prof. C. W. Woodworth of the University of Cali- Vv vl PREFACE fornia; Prof. G. Macloskie of Princeton University; Prof. W. A. Locy of Northwestern University; Prof. J. G. Neédham of Lake Forest University; Dr. S. H. Scudder of Cambridge, Mass.; Dr. George Dimmock of Springfield, Mass.; Dr. Howard Ayers of Cincinnati, Ohio; Dr. W. M. Wheeler of the American Museum of Natural History, New York City; Dr. W. L.- Tower of the University of Chicago; (Drama Mayer, Director of the Marine Biological Laboratory, Tortu- gas, Fla.; James H. Emerton of Boston, Mass.; Dr. and Mrs. G. W. Peckham of Milwaukee, Wis.; Dr. Henry C. McCook of Devon, Penn.; Dr. William Trelease, Director of the Mis- souri Botanical Garden; Dr. Henry Skinner, as editor of ‘‘ En- tomological News ”’ ; the editors of “ The American Natural- ist’; and W. Saville-Kent, of Wallington, England. Acknowledgments are further due to the Boston Society of Natural History, the American Philosophical Society and the Academy of Science of St. Louis. Courteous permission to use certain figures was given also by The Macmillan Co.; Henry Holt & Co.; Ginn & Co. ; Prot. Carl Chun of Leipzig; F. Ditmmler of Berlin, publisher of Kolbe’s Einfihrung; and Gustav Fischer of Jena, publisher of Hertwig’s Lehrbuch and Lang’s Lehrbuch. CONTENTS (CHAPTER MSO AT TONE 2 2 sf isck a cate os ak ee Badd ts MieeemATOMY AND PHYSIOLOGY ........<..0200 awe s MMB rn MOP NLEANE sicgcte a x ol.c coos. anit aleelee atdeloe bles INE AWAPTATIONS OF AQUATIC INSECTS ...5....0.006-0 Pee MmoR PANT). COLORATION. .. o..cib. feos hems aee coe en Pee NE REV E- COLORATION. <..6 5 5 cles cis sone ota ee ae whee VIL. Oricin OF ADAPTATIONS AND OF SPECIES .......... PiemnSEeTS IN RELATION TO PLANTS .. 2.0005 be oe. aeen ieee iNsecTs IN RELATION TO OTHER ANIMAS ...<.... ReBUMPERREEATIONS OF INSECTS ....0.is.dam cave oes PMI EOM SE TPAWIOR | 7 aj... .12s ae onus os o0 mee he ne eww. o8 POMS AREBUNION 6 o-. ¢ ——— SS YW ~ a \ YS NY Ah AMAR \ \ Y Yj \ \ SSSSSS i N\ 2977 B Antenne of mosquito, Culex pipiens. A, male; B, female. (suctorial). Collembola and Hymenoptera, however, com- bine both functions; Diptera, though suctorial, exhibit various modifications for piercing, lapping or rasping; Thysanoptera are partly mandibulate but chiefly suctorial; and adult Ephe- merida and Trichoptera have but rudimentary mouth parts. The mandibulate orders are Thysanura, Collembola (pri- marily), Orthoptera, Platyptera, Plecoptera, Ephemerida (rudimentarily in adult), Odonata, Neuroptera, Mecoptera and Coleoptera. The mouth parts of an insect consist typically of labrum, mandibles, maxille, labiwm and hypopharyny (Fig. 44), though these organs differ greatly in different orders of in- sects. The mandibulate, or primary type, from which the suctorial, or secondary type, has been derived, will be consid- ered first. Mandibulate Type.—The labrum, or upper lip, in biting ANATOMY AND PHYSIOLOGY 37 insects is a simple plate, hinged to the clypeus and moving up and down, though capable of protrusion and retraction to some extent. It covers the mandibles in front and pulls food back to these organs. On the roof of the pharynx, under the la- Fic. 44. Mouth parts of a cockroach, Ischnoptera pennsylvanica. A, labrum; B, mandible; C, hypopharynx; D, maxilla; E, labium; c, cardo; g (of maxilla), galea; g (of labium), glossa; J, lacinia; /p, labial palpus; m, mentum; mp, maxillary palpus; p, paraglossa; pf, palpifer; pg, palpiger; s, stipes; sm, submentum. B, D and E are in ventral aspect. brum and clypeus, is the epipharynx; this consists of teeth, tubercles or bristles, which serve in some insects merely to hold food, though as a rule the epipharynx in mandibulate insects bears end-organs of taste (Packard). The mandibles, or jaws proper, move in a transverse plane, being closed by a pair of strong adductor muscles and opened by a pair of weaker abductors. The mandible is almost always a single solid piece. In herbivorous insects (Fig. 45, A) it is compact, bluntly toothed, and often bears a molar, or crushing, surface behind the incisive teeth. In carnivorous 38 ENTOMOLOGY species (B) the mandible is usually long, slender and sharply toothed, without a molar surface. Various forms of mandibles. Often, as in soldier ants, - G H Ty 1 4 A, Melanoplus; B, Cicindela; C, Apis; D, Onthophagus; E, Chrysopa; F-I, soldier termites (after HaGEN). the mandibles are used as piercing weapons; in bees (C) they are used for various industrial purposes; in some beetles they "iG. 46. Maxilla of caliginosus, DECLAaGr l, lacinia; p, palpus; pf, Harpalus ventral as- cardo; g, galea; palpifer; s, subgalea. stipes; sg, are large, grotesque in form and appa- rently purposeless. The Onthophagus (D) and many other dung beetles consist chiefly of a flexible lam- mandibles of ella, admirably adapted for its special purpose. In Euphoria (Vig. 261), which feeds on pollen and the juices of fruits, the mandibles, and the other mouth parts as well, are densely clothed with In the larva of Chrysopa, the inner face of the mandible (Fig. 45, £) has a longitudinal groove against which hairs. the maxilla fits to form a canal, through which the blood of plant lice is sucked In termites (F—/) the mandibles assume curious and often into the cesophagus. inexplicable forms. Next in order are the mazille, or under jaws, which are less powerful than the mandibles and more complex, consisting as they do of several sclerites (Figs. 44, 46). Essentially, the ANATOMY AND PHYSIOLOGY 39 maxilla consists of three lobes, namely, palpus, galea and Jacima, which are borne by a stipes, and hinged to the skull by means of a cardo. The palpus, always lateral in position, is usually four- or five-jointed and is tactile, olfactory or gus- tatory in function. The lacinia is commonly provided with teeth or spines. The maxillz supplement the mandibles by holding the food when the latter open, and help to comminute the food. Additional maxillary sclerites, of minor impor- tance, often occur. The labium, or under lip, may properly be likened to a united pair of maxille, for both are formed on the same three-lobed plan. This correspondence is evident in the cockroach, among other gener- alized insects. Thus, in this insect (Fig. 44) : BIG. 47: Lasium = MAXILLz palpus = palpus paraglossa = galea glossa = lacinia palpiger = palpifer mentum = stipites submentum with gula= cardines In most mandibulate orders the gloss unite to form a single median A : Labium of Harpalus caligi- organ, as in Harpalus (Fig. 47; 2). mosus, ventral aspect. gg, : s : united glosse, termed the The labium forms the floor of the iss ema: one pharynx and assists in carrying food ?s, balpiEes eben : isos sm, submentum. e median to the mandibles and maxillz. Sortion of the labiunr beyond * the mentum is termed the The use of the term eee ’ ce second maxille’’ for the labium of an in- sect is open to objection, as it implies an equivalence with the second maxillz of Crustacea—which is by no means established. The tongue, or hypopharyns, is a median fleshy organ (Fig. 44) which is usually united more or less with the base of the labium. In insects in general, the salivary glands open at the 40 ENTOMOLOGY base of the hypopharynx. In the most generalized insects, Thysanura and Collembola, the hypopharynx is a compound organ, consisting of a median ventral lobe, or lingua, and two dorso-lateral lobes, termed superlingue by the author. Superlinguz occur in a few other mandibulate orders (Orthop- tera, Fig. 48; Ephemerida, Fig. 49), but have not yet been recognized in the more specialized orders of insects. Suctorial Types.—Owing to their greater complexity, suctorial mouth parts Deere reser ne are not nearly so well understood as the lingua; s, superlingua— mandibulate organs, but enough has been After Hansen. : learned to enable us to homologize the two types, even though morphologists still disagree in regard to minor details of interpretation. The suctorial, or haustellate, orders are Collembola (in part), Thysanoptera (in part), Hemiptera, Trichoptera (im- perfectly), Lepidoptera, Dip- Fic. 48. tera, Siphonaptera and Hy- age menoptera (which have \\ Wh/ A functional mandibles, how- s ee ever). Hemiptera. — The beak, or rostrum, in Hemiptera O consists (Fig. 50) of a Hypopharynx of an ephemerid, Hepta- conspicuous, one- to four- genia. (PO Akgovenbeyy Gi Git superlinguze.— oie : : After VAYSSIERE. jointed labium, which en- sheathes hair-like mandibles and maxille and is covered above at its base by a short labrum. The mandibles and max- ill are sharply-pointed, piercing organs and the former fre- quently bear retrorse barbs just behind the tip; the two max- illee lock together to form a sucking tube. Though primarily a sheath, the labium bears at its extremity sensory hairs, which are doubtless used to test the food. This general description applies to all Hemiptera except the parasitic forms, which pre- ANATOMY AND PHYSIOLOGY 4! sent special modifications. A pharyngeal pumping apparatus is present, which is similar in its general plan to that of Lepi- doptera and Diptera, as presently described, though it differs as regards the smaller details of construction. Fic. 50. D Mouth parts of a hemipteron, Benacus griseus. A, dorsal aspect; B, transverse sec- tion; C, extremity of mandible; D, transverse section of mandibles and maxille; c, canal; 7, labrum; /i, labium; m, mandible; mx, maxille. Lepidoptera.—In Lepidoptera, excepting Eriocephala, the labrum is reduced (Fig. 51) and the mandibles are either rudi- mentary or absent (Rhopalocera). The two maxillz are rep- resented by their galeze, which form a conspicuous proboscis ; the grooved inner faces of the galee (or laciniz, according to Kellogg) form the sucking tube, which opens into the cesoph- agus. The labium is reduced, though the labial palpi (Fig. 52) are well developed. The so-called rudimentary mandi- bles of Anosia and other forms have been shown by Kellogg to be lateral projections of the labrum (Fig. 51) and he terms them pilifers. ENTOMOLOGY The exceptional structure of the mouth parts in the gene- ralized genus Eriocephala (Muicropteryx) sheds much light on Phlegethontius moth, clypeus; e, eye; /, labrum; m, mandible; p, pilifer; pr, proboscis. Head of a sexta. sphingid a, antenna; c, is essentially like that of Diptera. at the skull and inserted on the wall of a pharyngeal bulb, serve to dilate the bulb that it may suck in fluids, while numerous circular muscles serve by contracting suc- cessively to squeeze the contents of the bulb back into the stomach ; a hypopharyngeal valve prevents their return forward. Diptera.—In the female mos- quito the mouth parts (Fig. 53) are long and slender. As Dim- mock has found, the labrum and epipharynx combine’ to form a sucking tube; the mandibles and maxillz are delicate, linear, piere- ing organs, the latter being barbed distally ; maxillary palpi are pres- *Kulagin, however, describes them as the morphology of these organs in other Lepidop- tera, as Walter and Kel- loge In this genus there are func- tional mandibles; the maxilla presents palpus, galea, lacinia, stipes and cardo, though there is no have shown. proboscis; the labium has well developed submen- tum, mentum and palpi;.a hypopharynx is present. The sucking apparatus, as described by Burgess, Five muscles, originating FTG: 52: Head of a butterfly, Vanessa. labial palpus; p, a, antenne; J, proboscis. remaining separate. ANATOMY AND PHYSIOLOGY 43 ent; the hypopharynx is linear also and serves to conduct sa- liva; the labium forms a sheath, enclosing the other mouth parts when they are not in use; a pair of sensory lobes, termed labella, occur at the extremity of the labium. Mouth parts of female mosquito, Culex pipiens. A, dorsal aspect; B, transverse section; C, extremity of maxilla; D, extremity of labrum-epipharynx; a, antenna; e, compound eye; h, hypopharynx; /, labrum-epipharynx; /i, labium; m, mandible; m-, maxilla; p, maxillary palpus.—B, after DImMMocK. The cesophagus is dilated to form a bulb, or sucking organ, from which muscles pass outward to the skull; when these con- tract, the bulb dilates and can suck in fluids, as blood or water, which are forced back into the stomach by the elasticity of the bulb itself, according to Dimmock; the regurgitation of the food is prevented by a valve. The male mosquito rarely if ever sucks blood and its mouth parts differ from those of the female in that the mandibles are A4 ENTOMOLOGY aborted and the maxille slightly developed, but with long palpi, while the hypopharynx coalesces with the labium, and there is no cesophageal bulb. Hymenoptera.—In the honey bee, which will serve as a type, the labrum (Fig. 54) is simple; the mandibles are well developed instruments for cutting and other purposes and the Fic. 54. x f es > as ri Tht > ene 173.1114) SVODN)IIDIP Mouth parts of the honey bee, Apis mellifera. a, base of antenna; br, brain; c, clypeus; h, hypopharynx; /, labrum; /p, labial palpus; m, mentum; mo, mouth; mx, maxilla; sm, submentum.—After CHESHIRE. remaining mouth parts form a highly complex suctorial appa- ratus, as follows. The tongue is a long flexible organ, ter- minating in a “spoon” (Fig. 127) and clothed with hairs of various kinds, for gathering nectar or for sensory or mechan- ical purposes. The maxille and labial palpi form a tube em- bracing the tongue, while the epipharynx fits into the space between the bases of the mavxille to complete this tube. Through this canal nectar is driven, by the expansion and con- traction of the tube itself, according to Cheshire, except that when only a small quantity of nectar is taken, this passes from the spoon into a fine “central duct,’ or also into the “ side ducts,” which are specially fitted to convey quantities of fluid too small for the main tube. For a detailed account of the highly complex and exquisitely adapted mouth parts of the honey bee, the reader is referred to Cheshire’s admirable work or to Packard’s Text-Book. Segmentation of the Head.—The determination of the — ANATOMY AND PHYSIOLOGY 45 number of segments entering into the composition of the insect head has been a difficult problem. As no segment bears more than one pair of primary appendages, there are at least as many segments in the head as there are pairs of primary appendages. On this basis, then, the antennz, mandibles, maxille and labium may be taken to indicate so many seg- ments; but in order to decide whether the eyes, labrum and hypopharynx represent segments, other than purely anatom- ical evidence is necessary. The key to the subject is furnished by embryology. At an early stage of development the future segments are marked off by transverse grooves on the ventral surface of the embryo, and the pairs of segmental appendages are all alike (Fig. 194), or equivalent, though later they dif- ferentiate into antennz, mouth parts, legs, etc. Moreover, the nervous system exhibits a segmentation which corresponds to that of the entire insect; in other words, each pair of primitive ganglia, constituting a mewromere, indicates a segment. Now in front of the cesophagus three primitive segments appear, each with its neuromere (Fig. 55) : first in position, an ocular seg- ment, destined to bear the compound eyes; second, an antennal segment; third, an intercalary (premandibular) segment, which in the generalized orders Thysanura and Collembola bears a transient pair of appendages that are probably homol- ogous with the second antennz of Crustacea. In the adult, the ganglia of these three segments have united to form the brain, and the original simplicity and distinctness have been lost. The labrum, by the way, does not represent a pair of appendages, but arises as a single median lobe. Behind the cesophagus, three embryonic segments are clearly distinguish- able, each with its pair of appendages, namely, mandibular, max- illary and labial. Finally, the hypopharynx, or rather a part of it, claims a place in the series of segmental appendages, as the author has maintained; for in Collembola its two dorsal con- stituents, or superlingue, develop essentially as do the other paired appendages and, moreover, a superlingual neuromere (Fig. 55) exists. The four primitive ganglia immediately 46 ENTOMOLOGY behind the mouth eventually combine to form the subcesopha geal ganglion. To summarize—the head of an insect is composed of at least six segments, namely, ocular, antennal, intercalary, mandibu- lar, maxillary and labial; and at most seven, since a superlin- gual segment occurs between the mandibular and maxillary segments in Collembola and probably Thysanura, though it has not yet been discovered in the more specialized insects. Fie. 55 @ 29 097280 9625 2° 390 6% A 209 0% © 25° S0962 Ce Vi fa 9 9% 999 ,°.0 a 02 909% 0 OOP e- 9°09 098oa 0098 earey Serge eof. ENS08 72 ,o8 @ 07 e 19 Og\" (3) 19 9) ye’ os BOO Or ee PLO #1520 yo gy Sor oo %6 909 ow F ! 7 & Oe 0 ©6 Red %9 ty > / 5 ° Paramedian section of an embryo of the collembolan Anurida maritima, to show the primitive cephalic ganglia. 1, ocular neuromere; 2, antennal; 3, intercalary; 4, mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic; a, antenna; /, labrum; /i, labium; FP, /, /3, thoracic legs; m, mandible; mx, maxilla. —After Foitsom. Thorax.—The thorax, or middle region, comprises the three segments next behind the head, which are termed, respec- tively, pro-, meso- and metathorax. In aculeate Hymenop- tera, however, the thoracic mass includes also the first abdom- inal segment, then known as the propodeum, or median seg- ment. Each of the three thoracic segments bears a pair of i ANATOMY AND PHYSIOLOGY 47 legs in almost all adult insects, but only the meso- and meta- thorax may bear wings. The differentiation of the thorax as a distinct region is an incidental result of the development of the organs of locomo- tion, particularly the wings. Thus in legless (apodous) larve the Se thoracic and abdominal segments are alike; when legs are present, but no wings, the thoracic segments are somewhat enlarged; and when wings occur, the size of a wing- bearing segment depends on the vol- ume of the wing muscles, which in turn is proportionate to the size of Diagram of the principal scle- rites of a thoracic segment. em, the wings. When wings are absent cpimeron; es, episternum; ?, : prescutum; pr, parapteron; ps, (as in Thysanura and Collembola) postscutellum; s, scutum; sl, BeMbenwor pairs, eqial in area (as cutlum) st sternum—Atter ComMsTOcK. in Termitidz, Odonata, Trichoptera and most Lepidoptera) the meso-and metathorax are equal. If the fore wings exceed the hind ones (Ephemeride, Hymenop- tera) the mesothorax is proportionately larger than the meta- thorax; as also in Diptera, where no hind wings occur. If the fore wings are small (Coleoptera) or almost absent (Sty- lopidze) the mesothorax is correspondingly smaller than the metathorax. The prothorax, which never bears wings, may be enlarged dorsally to form a protective shield, as in Orthop- tera, Hemiptera and Coleoptera; or, on the contrary, may be greatly reduced, as in Ephemerida, Odonata, Lepidoptera and Hymenoptera. In the primitive Apterygota the prothorax may become reduced (many Collembola) or slightly enlarged (Lepisma). The dorsal wall of a thoracic segment is termed the notum, or tergum; the ventral wall, the sternum; and each lateral wall, a pleuron; the restriction of these terms to particular segments of the thorax being indicated by the prefixes pro-, meso- or meta-. These parts are usually divided by sutures into dis- 48 ENTOMOLOGY tinct pieces, or sclerites, as represented diagrammatically in Fig. 56. Thus the tergum of a wing-bearing segment is re- garded as being composed of four sclerites (tergites, Fig. 57), namely and in order, prescutum, scutum, scutellum and post- scutellum. The scutum and scutellum are commonly evident, but the two other sclerites are usually small and may be absent. Each pleuron consists chiefly of two sclerites (pleurites, Fig. 58), separated from each other by a more or less oblique suture. The anterior of these two, which joins the sternum, is termed the episternum; the other, the epi- meron. The former is divided into two sclerites in Odonata and both are so divided in Neuroptera. The sternum, though usually a single plate, is in some in- stances divided into halves, as Dorsal ‘aspect of the thorax. Of 2.if the cockroach, (onlay: ian beetle, Hydrous piceus. I, pronotum; 2, mesoprescutum; 3, mesoscutum; 4 five sclerites (Forficulide ). mesoscutellum; 5, mesopostscutellum; 6, metaprescutum; 7, metascutum; 8, To these should be added the a pair metascutellum; 9, metapostscutellum. Gh id tera —After NEwport. patagia of Lep Op ¢ of erectile appendages of the prothorax; and the paraptera, or tegule, of Lepidoptera and a pair of small sclerites at the bases of the EIGeS7: Hymenoptera front wings. Each thoracic segment bears a pair of spiracles in the em- bryo and in some adults as well (Campodea, Heteroptera), but in most imagines there are only two pairs of thoracic spiracles, the suppressed pair being usually the prothoracic. The sclerites of the thorax owe their origin probably to local strains on the integument, brought about by the muscles of the thorax. Thus the primitively wingless Thysanura and Collembola have no hard thoracic sclerites, though certain ANATOMY AND PHYSIOLOGY 49 creases about the bases of the legs may be regarded as incipi- ent sutures, produced mechanically by the movements of the Fic. 58. 3, proepimeron; 4, coxal cavity; 5, inflexed side of pronotum; 6, mesosternum; 7, meso- episternum; 8, mesoepimeron; 9, metasternum; 0, antecoxal piece; 11, metaepisternum; I2, metaepimeron; 13, inflexed side of elytron; a, sternum of an abdominal segment; an, antenna; c, coxa; f, femur; /p, labial palpus; md, mandible; mp, maxillary palpus; t, trochanter; tb, tibia; ts, tarsus. Ventral aspect of a carabid beetle, Galerita janus. 1, prosternum; 2, proepisternum, legs. In soft nymphs and larve, the sclerites do not form until the wings develop; and in forms that have nearly or quite lost their wings,as Pediculide, Mallophaga, Siphonaptera and some 5 50 ENTOMOLOGY parasitic Diptera, the sclerites of the thorax tend to disappear. Furthermore, the absence of sclerites in the prothorax is prob- ably due to the lack of prothoracic wings, notwithstanding the so-called obsolete sutures of the pronotum in grasshoppers. Endoskeleton.—An insect has no internal skeleton, strictly speaking, though the term endoskeleton is used in reference to certain ingrowths of the external cuticula which serve as me- chanical supports or as protections for some of the internal organs. The tentorium of the head has al- ready been referred to. ~ Vinggtue thorax three kinds of chitinous in- growths may be distinguished ac- cording to their positions: (1) phrag- mas, or dorsal projections; (2) apodemes, lateral; (3) apophyses, ventral. The phragmas (Fig. 59) are commonly three large plates, pertaining to the meso- and meta- thorax, and serving for the origin of indirect muscles of flight in Lepidoptera, Diptera, Hymenoptera and other strong-winged orders. The apodemes are comparatively small in- erowths, occurring sometimes in all Transverse sections of the thoracic segments of a beetle, three thoracic segments, though usu- Goliathus, to show the endo- 3 : skeletal processes. A, pro ally absent in the prothorax. ~ Phe thorax; 8, mesothorax; ©. apophyses occur in each thera@terer= metathorax; a, ad, apophyses; ad, apodeme; p, phragma— ment as a pair of conspicuous proc- Sete esses, which either remain separate or else unite more or less; leaving, however, a passage for the ventral nerve cord. These endoskeletal processes serve chiefly for the origin of muscles concerned with the wings or legs, and are absent in such wingless forms as Thysanura, Pediculide and Mal- lophaga. ANATOMY Some ambiguity attends the use of these terms. AND PHYSIOLOGY 51 Thus some writers use the term apodemes for apophyses and others apply the term apodeme to any of the three kinds of ingrowths. Legs.—In almost all adult insects and in most larve each of the three thoracic segments bears a pair of legs. The leg is articulated to the sternum, episternum and epimeron and consists of five seg- ments (Fig. 60), in the following order: tarsus. coxa, trochanter, femur, tibia, The coxa, or basal segment, often has a The trochanter is small, and in_ parasitic posterior sclerite, the trochantine.' Hymenoptera consists of two subseg- ments. The femur is usually stout and conspicuous, the tibia commonly slender. The tarsus, rarely single-jointed, consists usually of five segments, the last of which bears a pair of claws in the adults of most orders of insects and a single claw in larve; between the claws in most imagines is a pad, usually termed the pulvillus, or empodium. Adaptations of Legs.—The legs ex- hibit a great variety of adaptive modifica- tions. A walking or running insect, as a Fic. 60. Leg of a beetle, Calo- soma calidum. c, coxa; cl, claws; f, femur; s, spur; #-#5, tarsal seg- ments; tb, tibia; ir, trochanter. carabid or cicindelid beetle (Fig. 62, 4) presents an average condition, as regards the legs. In leaping insects (grasshop- pers, crickets, Haltica) the hind femora are enlarged (B) to accommodate the powerful extensor muscles. In insects that make little use of their legs, as May flies and Tipulidz, these appendages are but weakly developed. The spinous legs of * But on account of the ambiguous use of this last term, the name meron (Fig. 61), proposed by Walton, is to be preferred. 52 EN TOMCLOGY dragon flies form a basket for catching the prey on the wing. Modifications of the front legs for the purpose of grasping occur in many insects, as the terrestrial families Mantide (C) and Reduviide and the aquatic families Belostomidze and Naucoride (D). Swim- ming species present special adaptations of the legs (Fig. 228), as described in the chapter on aquatic insects. In digging insects, the fore Fic. 61. legs are expanded to form shovel-like organs, notably Left hind leg of Bittacus. c, coxa in the mole-cricket (Fig. 62, genuina; em, epimeron; es, episternum; f, EB), in which the fore tibia’ femur; m, meron; f, trochanter. has some resemblance to the human hand, while the tarsus and tibia are remarkably adapted for cutting roots, after the manner of shears. The Scara- beeidze have fossorial legs, the anterior tarsi of which are in some genera reduced (F) or absent; they are rudimentary in the female (G) of Phaneus carnifex and absent in the male (H), and absent in both sexes of Deltochilum. Though females of Phaneus lose their front tarsi by digging, the de- generate condition of these organs cannot be attributed to the inheritance of a mutilation, but may have been brought about by disuse; though no one has explained why the two sexes should differ in this respect. Many insects use the legs to clean the antennz, head, mouth parts, wings or legs; the honey bee (with other bees, also ants, Carabidz, etc.) has a special antenna-cleaner on the front legs (Fig. 263, D), which is described, with other interesting modifications of the legs, on page 271. Indeed, the legs serve many such minor purposes in addi- tion to locomotion. They are generally used to hold the female during coition, and in several genera of Dytiscidze (Dytiscus, Cybister) the male (Fig. 62, /) has tarsal disks and cupules, chiefly on the front tarsi, for this purpose. Among wm Ww ANATOMY AND PHYSIOLOGY line, (67), f A, Cicindela sexguttata; B, Nemobius vittatus, Adaptive modifications of the legs. hind leg; C, Stagmomantis carolina, left fore leg; D, Pelocoris femorata, right fore leg; E, Gryllotalpa borealis, left fore leg; F, Canthon levis, right fore leg; G, Phaneus carnifex, fore tibia and tarsus of female; H, P. carnifex, fore tibia of male; I, Dytis- cus fasciventris, right fore leg of male; c, coxa; f, femur; s, spur; f, trochanter; tb, tibia; ts, tarsus. 54 ENTOMOLOGY other secondary sexual peculiarities of the legs may be men- tioned the tibial brushes of the male Catocala concumbens, regarded as scent organs, and the queer appendages of male Foot of honey bee, Apis mel- lifera. c, c, claws; p, pulvillus; #815, tarsal segments.—After CHESHIRE. Dolichopodidz that dangle in the air as these flies pertommryinem dances. The pulvillus is commonly an adhesive organ. In flies it has glandular hairs that enable the in- sects to walk on smooth surfaces and to walk upside down; so also in many beetles and notably in the honey bee (Fig. 63); in this insect the pulvillus is released rapidly from the surface to which it has been applied, by rolling up from the edges inward. Sense organs occur on the legs. Thus tactile hairs are almost always present on these appendages, while auditory organs occur on the front tibize of Locustidze, Gryllidz and some ants. Finally, the legs may be used to produce sound, Fic. 64. Caterpillar of Phlegethontius sexta. Natural size. ANATOMY AND PHYSIOLOGY 55 as in Stenobothrus and such other Acridiidz as stridulate by rubbing the femora against the tegmina. Legs of Larve.—Thoracic legs, terminating in a single claw, are present in most larvee. Caterpillars have, in addi- tion, fleshy abdominal legs (Fig. 64) ending in a circlet of hooks. Most caterpillars have five pairs of these legs (on abdominal segments 3, 4, 5, 6 and 10), but the rest vary in this respect. Thus Lagoa has seven pairs (segments 2-7 and 10) and Geometridz two (segments 6 and 10), while a few caterpillars (Tischeria, Limacodes) have none. Larve of Fic. 65. Mechanics of an insect’s leg. a, axis of coxa; c, coxa; cl, claw; e, extensor of tibia; ec, extensor of claw; et, extensor of tarsus; f, flexor of tibia; fc, flexor of claw; ft, flexor of tarsus; 7, r, rotators of coxa; s, spur; t, trochanter muscle (elevator of femur); ti, tibia —After GRABER. saw flies (Tenthredinide) have seven or eight pairs of abdom- inal legs and larve of most Panorpide, eight pairs. Nota few coleopterous larve (some Cerambycide, Phytonomus) also have abdominal legs, which are incompletely developed, however, as compared with those of Lepidoptera. The legless, or apodous, condition occurs frequently among larve and always in correlation with a sedentary mode of life; as in the larve of many Cerambycide, nearly all Rhynchoph- ora, a few Lepidoptera, all Diptera, and all Hymenoptera ex- cept Tenthredinidz, Siricide, and other Terebrantia. 56 EN TOMOLOGY Among adult insects, female scale insects are exceptional in being legless. Walking.—An adult insect, when walking, normally uses its legs in two sets of three each; thus the front and hind legs of one side and the middle leg of the other move forward almost simultaneously—though not quite, for the front leg mid Muscles of left leg of a cockroach, pos- terior aspect. abc, ab- ductorm of | coxa; yadc, adductor of coxa; ef, extensor of femur; et, extensor of tibia; ff, flexor of femur; ft, flexor of tibia; fta, flexor of tarsus; rt, re- tractor of tarsus.—After MraAtt and DENNY. moves a little before the middle one, which, in turn, precedes the hind leg. During these movements the body is sup- ported by the other three legs, as on a tripod. The front leg, having been ex- tended and its claws fixed, pulls the body forward by means of the contraction of the tibial flexors; the hind leg, on the contrary, pushes the body, by the short- ening of the tibial extensors, against the resistance afforded by the tibial spurs; the middle leg acts much like the hind one, but helps mainly to steady the body. Different species show different peculiari- ties of gait. In its analysis, the walking of an insect is rather intricate, as Graber and Marey have shown. The mode of action of the principal leg muscles may be gathered from Fig. 65. Here the flexion of the tibia would cause the tibial spur (s) to describe the line s z; and the backward movement of the leg due to the upper coxal rotator r would cause the spur to follow the are s 3. As the resultant of both these movements, the path actually described by the tibial spur is s 2; then, as the leg moves forward, the curve is con- tinued into a loop. Caterpillars use their legs successively in pairs, and when the pairs of legs are few and widely separated, as in Geomet- ridz, a curious looping gait results. ANATOMY AND PHYSIOLOGY 57, The leg muscles of a cockroach are shown in Fig. 66. Leaping.—The hind legs, inserted nearest the center of gravity, are the ones employed in leaping, and they act to- gether. A grasshopper prepares to jump by bending the femur back against the tibia; to make the jump, the tibia is jerked back against the ground, into which the tibial spurs are driven, and the straightening of the leg by means of the pow- erful extensors throws the insect into the air. At the distal end of the femur are two lobes, one on each side of the tibia, which prevent wobbling movements of the tibia. Wings.—The success of insects as a class is to be attributed largely to their possession of wings. hese and the mouth parts, surpassing all the other organs as regards range of dif- ferentiation, have furnished the best criteria for the purposes of classification. The wings of insects present such countless differences that an expert can usually refer a detached wing to its proper genus and often to its species, though no less than three hundred thousand species of insects are already known. Typically, there are two pairs of wings, attached respec- tively to the mesothorax and the metathorax, the prothorax never bearing wings, as was said. When only one pair is present it is almost invariably the anterior pair, as in Diptera and male Coccidz, though in male Stylopidz it is the posterior pair, the fore wings being rudimentary. In bird lice, fleas and most other parasitic insects, the wings have degenerated through disuse. In Thysanura and Collem- bola there are no traces of wings even in the embryo; whence it is inferred that wings originated later than these orders of insects. Miller and Packard have regarded the wings as tergal out- growths; Tower, however, has recently shown that the wings of Coleoptera, Orthoptera and Lepidoptera are pleural in ori- gin, arising just below the line where later the suture between the pleuron and tergum will originate, though the wings may subsequently shift to a more dorsal position. 58 ENTOMOLOGY Modifications of Wings.—Being commonly more or less triangular, a wing presents three margins: front (costal), outer (apical) and inner (anal). Various modifications occur in the front wings, which are in many orders more useful for protection than for flight. Thus, in Orthoptera, they are leathery, and are known as ftegmina; in Coleoptera they are usually horny, and are termed elytra; in Heteroptera, the base of the front wing is thickened and the apex remains mem- branous, forming a hemelytron. Diptera have, in place of the hind wings, a pair of clubbed threads, known as balancers, or halteres, and male Coccidze have on each side a bristle that hooks into a pocket on the wing and serves to support the lat- ter. In many muscid flies a doubly lobed membranous squama occurs at the base of the wing. In Hymenoptera the front and hind wings of the same side are held together by a row of hooks (hamuli) ; these are situ- ated on the costal margin of the hind wing and clutch a rod- like fold of the fore wing. In very many moths, the two wings are enabled to act as one by means of a frenulum, con- sisting of a spine or a bunch of bristles near the base of the hind wing, which, in some forms, engage a membranous loop on the fore wing. Venation, or Neuration.—A wing is divided by its veins, or nervures, into spaces, or cells. The distribution of the veins is of great systematic importance but, unfortunately, the homologies of the veins in the different orders of insects have not been fixed, until recently, so that no little confusion has existed upon the subject. For example, the term discal cell, used in descriptions of Lepidoptera, Diptera, Trichoptera and Psocide, has in no two of these groups been applied to the same cell. The admirable work of Comstock and Needham, however, seems to settle this disputed subject. _ By a study of the tracheze which precede and, in a broad way, determine the positions of the veins, these authors have arrived at a primi- tive type of tracheation (Fig. 67) to which the more complex types of tracheation and venation may be referred. ANATOMY AND PHYSIOLOGY 59 In general, the following principal longitudinal veins may be distinguished, in the following order: costa, subcosta, radius, media, cubitus and anal (Figs. 67-71). ETGs076 * M1 RS ( : M2 ul M4 A Cu2 34a. 2daA Ist Hypothetical type of venation. A, anal vein; C, costa; Cu, cubitus; M, media; R, radius; Sc, subcosta—Figs. 67-71 after Comstock and NEEDHAM. The costa (C) strengthens the front margin of the wing and is essentially unbranched. The subcosta (Sc) is close behind the costa and is un- branched in the imagines of many orders in which there are few wing veins, though it is typically a forked vein. The radius (2), though subject to much modification, 1s typically five-branched, as in Fig. 67. The second principal branch of the radius is termed the radial sector (its). The media (MV) is often three-branched and is typically four-branched, according to Comstock and Needham. The cubitus (Cw) has two branches. The anal veins (4) are typically three, of which the first is generally simple, while the second and third are many- branched in wings that have an expanded anal area. The Plecoptera, as a whole, show the least departure from the primitive type of venation; which is well preserved, also, in the more generalized of the Trichoptera. Starting from the primitive type, specialization has occurred in two ways: by reduction and by addition. Reduction oc- curs either by the atrophy of veins or by the coalescence ot two or more adjacent veins. Atrophy explains the lack of all but one anal vein in Rhyphus (Fig. 68) and other Diptera, 60 ENTOMOLOGY and the absence of the base of the media in Anosia (Fig. 69) and many other Lepidoptera; in the pupa of Anosia, the media may be found complete. Coalescence “takes place in two ways: first, the point at which two veins separate occurs nearer and Fic. 68. Wing of a fly, Rhyphus. Lettering as before. nearer the margin of the wing, until finally, when the margin is reached, a single vein remains where there were two before; second, the tips of two veins may approach each other on the margin of the wing until they unite, and then the coalescence Wing of a butterfly, Anosia. Lettering as before. proceeds towards the base of the wing.’’ (Comstock and Need- ham.) The former, or outward, kind of coalescence is com- mon in most orders of insects; the latter, or award, kind is especially prevalent in Diptera. Specialization by addition occurs by a multiplication of the branches of the principal veins. ANATOMY AND PHYSIOLOGY 61 Comstock and Needham have succeeded in homologizing practically all the types of neuration, including such perplex- ‘ing types as those of Ephemerida (Fig. 70), Odonata (Fig. 20, B) and Hymenoptera (Fig. 71), and their thorough work affords a sound basis for a rational terminology of the wing Wings of a May fly. Lettering as before. veins; there is no longer any excuse for the lamentable confu- sion that has hitherto attended the study of venation. Folding of Wing.—In some beetles (as Chrysobothris) the wings are no larger than the elytra and are not folded; in A typical hymenopterous wing. Lettering as before. others, however, the wings exceed the elytra in size, and when not in use are folded under the elytra in ways that are simple but efficient, as described by Kolbe and by Tower. To be understood, the process of folding should be observed in the living insect. As described by Tower for the Colorado potato 62 EN TOMOLOGY beetle, the folded wing (Fig. 72, B) exhibits a costal joint (a), a fold parallel to the transverse vein (b), and a complex joint at d. The wing rotates upon the articular head (ah) and when folded back beneath the wing-covers the inner end of the cotyla (c) is brought into contact with a chitin- Ere: 72) Wing of Leptinotarsa decemlineata. A, spread; B, folded; a, costal joint; ah, articular head; an, anterior system of veins; b, transverse vein; c, cotyla; d, joint; m, middle system of veins; p, posterior system of veins.—After Tower. ous sclerite of the thorax, which stops the further movement of the cotyla medianward, and as the wing swings farther back the middle system of veins (7) is pushed outward and ante- riorly. This motion, combined with the backward movement of the wing as a whole, produces the folding of the distal end of the wing. There are no traces of muscles or elastic liga- ments in the wing which could aid in the folding. Mechanics of Flight.—The mechanism of insect flight is much less complex than one might anticipate. Indeed, owing to the structure of the wing itself, simple up and down move- ments are sufficient for the simplest kind of flight. During ANATOMY AND PHYSIOLOGY 63 oscillation, the plane of the wing changes, as may be demon- strated by holding a detached wing by its base and blowing at right angles to its surface; the membrane of the wing then yields to the pressure of the air while the rigid anterior margin does not, to any great extent. Similarly, as the wing moves down- ward the membrane is inclined upward by the resistance of the air, and as the wing moves upward the membrane bends down- ward. Therefore, by becoming deflected, the wing encounters a certain amount of resistance from behind, which is sufficient to propel the insect. The faster the wings vibrate, the greater the deflection, the greater the resistance from be- hind, and the faster the flight of the insect. The path traced in the air by Trajectory of the wing jof an insect. BGs 73: a rapidly vibrating wing may be determined by fastening a bit of gold leaf to the tip of the wing and allowing the insect—a wasp, for example—to vibrate its wings in the sunlight, against a dark background. Under these conditions, the trajectory of the wing appears as a lumi- nous elongate figure 8. During flight, the trajectory consists of a continuous series of these figures, as in Fig. 73. Marey, the chief authority on animal locomotion, used chronophotography, among other methods, in studying the process of flight, and obtained at first twenty, and later one hundred and ten, successive photographs per second of a bee in flight. As the wings were vibrating 190 times per second. however, the images evidently represented isolated and not consecutive phases of wing movement. Nevertheless, the images could be interpreted without difficulty, in the light of the results obtained by other methods. At length he obtained sharp but isolated images of vibrating wings with an exposure of only 1/25,000 of a second. The frequency of wing vibration may be ascertained from the note made by the wing—if it vibrates rapidly enough to 64 ENTOMOLOGY make one; and, in any case, may be determined graphically by means of a kymograph, which, in one of its forms consists of a cylinder covered with smoked paper and revolved by clock- work at a uniform rate. The insect is held in such a position that each stroke of the wing makes a record on the smoked paper, as in Fig. 74. Comparing this record with one made FIG. 74. NVNE RNS SN NUNN URN Ras em h eset NUNN aes ea sa asanaaaraasaas Records of wing vibration. A, mosquito, Anopheles. Above is the wing record and below is the record of a tuning fork which vibrated 264.6 times per second. B, wasp, Polistes. The tuning fork in this instance had a vibration frequency of 97.6. on the same paper by a tuning fork of known vibration period, the frequency of wing vibration can be determined with great accuracy. As the wing moves in the arc of a circle, the radius of which is the length of the wing, the extreme tip of the wing records only a short mark; if, however, the wing is pressed against the smoked cylinder, a large part of the figure 8 trajec- tory may be obtained, as in Fig. 74, B. The wings of the two sides move synchronously, as Marey found. The smaller the wings are, the more rapidly they vibrate. Thus a butterfly (P. rape) makes g strokes per second, a dragon fly 28, a sphingid moth 72, a bee I90 and a house fly 33 Wing Muscles.—The base of a wing projects into the thoracic cavity and serves for the insertion of the direct mus- cles of flight. Regarding the wing as a lever (Fig. 75, A), ANATOMY AND PHYSIOLOGY 05 with the fulcrum at /, it is easy to understand how the con- traction of muscle e raises the wing and that of muscle d low- ers it. These muscles are shown diagrammatically in Fig. 75, B. Besides these, there are certain muscles of flight which act indirectly upon the wings, by altering the form of the thoracic wall. Thus the muscle ie (Fig. 75, B) elevates the wing by pulling the tergum toward the sternum; and the longitudinal muscle 7d depresses the wing indirectly by arching the tergum of the thorax. Dienea up. and down movements are all that are necessary for the simplest kind of insect flight, the process becomes com- plex in proportion to the efficiency of the flight. Thus in dragon flies there are nine A, diagram to illustrate the action of the wing muscles to each wing: muscles of an insect. B, diagram of wing mus- Fs cles. a, alimentary canal; cn, muscle for con- five depressors, three tracting the thorax, to depress the wings; d, de- elevators and one ad- pressor of wing; e, elevator of wing; ex, muscle for expanding the thorax, to elevate the wings; ductor. id, indirect depressor; ie, indirect elevator; /, leg Abdomen on aS h e muscle; p, pivot, or fulcrum; s, sternum; f¢, ter- : ? b gum; wg, wing.—After GRABER. chief functions of the abdomen are respiration and reproduction, to which should be added digestion. The abdomen as a whole has undergone less differentiation than the thorax and presents a simpler and more primitive segmentation. Segments.—A typical abdominal segment bears a dorsal / 5 6 66 ENTOMOLOGY plate, or tergum, and a ventral plate, or sternum, the two being connected by a pair of pleural membranes, which facilitate the respiratory movements of the tergum and sternum. Most of the abdominal segments have spiracles, one on each side, situ- ated in or near the pleural membranes of the first seven or eight segments. The total number of pairs of spiracles is as follows: Thoracic. Abdominal. Total. Campodea, 3 9) 3 Japyx, 4 F II Machilis, 2 7 9 Lepisma, 2 8 10 Blattide, Acridiide, 2 8 10 Odonata, 2 8 10 Heteroptera, 3 7 10 Lepidoptera, 2 7 9 Diptera, 2 7 ) In most embryo insects there are eleven pairs of spiracles (three thoracic and eight abdominal) ; in adults, however, two pairs are commonly suppressed—the prothoracic and the eighth abdominal. Number of Abdominal Segments.—Though consisting typically of ten segments—the number evident in such general- ized insects as Thysanura and Ephemerida—eleven occur in va- rious adult Orthoptera, with traces of a twelfth, while Hey- mons has detected twelve abdominal segments in embryos of Orthoptera and Odonata. In the more specialized orders, ten may usually be distinguished with more or less difficulty, though the number is apparently, and in some cases actually less, owing to modifications of the base of the abdomen in relation to the thorax, but especially to modifications of the extremity of the abdomen, for sexual purposes. Modifications.—In aculeate Hymenoptera the first segment of the abdomen has been transferred to the thorax, where it is known as the propodeum,or median segment; in other words, what appears to be the first abdominal segment is actually the second; this, as in bees and wasps, often forms a petiole, which enables the sting to be applied in almost any direction. In Cy- nipide the tergum of segment two or three occupies most of the ANATOMY AND PHYSIOLOGY 67 abdominal mass, the remaining segments being reduced and inconspicuous. The terminal segments of the abdomen often telescope into one another, as in lie, 70) many Coleoptera and Hymenop- tera (Chrysidide), or undergo other modifications of form and 2 position which obscure the seg- mentation. As tothe number of 3 evident (not actual) abdominal segments, Coleoptera show five or six ventrally and seven or eight dorsally; Lepidoptera, seven in the female and eight in the male; Diptera, nine (male Tipulidz) or only four or five; and Hymenop- tera, nine (Tenthredinidz) or as few as three (Chrysidide). In the larve of these insects, how- ever, nine or ten abdominal seg- ments are usually distinguishable, though the tenth is frequently modified, being in caterpillars TD united with the ninth. Appendages.—Rudimentary ab- Ventral aspect of the abdomen z : : of a female Machilis maritima, to dominal limbs occur in Thysanura iow, rudimentary limbs (a). of (Machilis, Fig. 76). Functional segments two to nine. (The left ? 7 : appendage of the ninth segment is abdominal legs do not occur in omitted.) c, ¢, ¢, cerci—After adult insects, but in larvee the ab- °°"***** dominal pro-legs (often called “ false legs,” Fig. 64) are ho- mologous with the thoracic legs and the other paired segmental appendages, as the embryology shows. The embryo of Gican- thus, according to Ayers, has ten pairs of abdominal appen- dages (Fig. 196), equivalent to the thoracic legs. Most of these embryonic abdominal appendages are only transitory, but the last three pairs frequently persist to form the genitalia, as in 68 ENTOMOLOGY Orthoptera (to which order Gicanthus belongs). In Collem- bola, the embryo has paired abdominal limbs, and those of the first abdominal segment eventually unite to form the peculiar ventral tube (Fig. 12) of these insects, while those of the fourth seg- ment form the character- istic leaping organ, or furcula. Cerci.—In many of the more generalized insects, Abdomen of female beetle, Cerambyx, in which the last three segments are used as an the abdomen bears at its ovipositor.—After Kose. extremity two or three appendages termed cerci. These occur in both sexes and are frequently long and multiarticulate, as in Thysanura (Figs. 76,9, 10) and Ephemerida (Figs. 19, 8; 84),though shorter in cockroaches and reduced to a single sclerite in Acridiide (Fig. 87). The paired cerci, or cercopoda of Packard, are usually though not always associated with the tenth abdominal seg- ment and are homologous with legs, as Ayers has found in CEcanthus and Wheeler in Xiphidiwm. -As to their function, the cerci of Thysanura are tac- Fic. 78. tile, and those of the cockroach olfactory, while the cerci of male Acridiidz Often serve to hold the female during copu- Abdomen of a female midge, Cecido- myia leguminicola, to show the pseudo- ovipositor. lation. Extremity of Abdomen.— Various modifications of the terminal segments of the abdo- men occur for the purposes of defzecation and especially repro- duction. The anus, dorsal in position, opens always through the last segment and is often shielded above by a suranal plate and on each side by a lateral plate. The genital orifice is al- ways ventral in position and occurs commonly on the ninth abdominal segment, though there is some variation in this re- spect. The external, or accessory, organs of reproduction are termed the genitalia. ANATOMY AND PHYSIOLOGY 69 Female Genitalia.—In Neuroptera, Coleoptera, Lepidoptera and Diptera the vagina simply opens to the exterior or else with the anus into a common chamber, or cloaca. Often, as in Cerambyx (Fig. 77) and Cecidomyia (Fig. 78) the attenu- Fic. 79. (E Ovipositor of Locusta. A, lateral aspect; B, ventral aspect; C, transverse section; c, cerci; d, dorsal valve; i, inner valve; v, ventral valve. The numbers refer to abdominal segments.—After Kortspe and DeEwivz. ated distal segments of the abdomen serve the purpose of an ovipositor ; thus in Cecidomytiidz, the terminal segments, tele- scoped into one another when not in use, form when extruded a lash-like organ exceeding frequently the remainder of the body in length. A true ovipositor occurs in Thysanura, Orthoptera, Odo- nata, Hemiptera, Hymenoptera and some other orders of in- sects. The ovipositor consists essentially of three pairs of valves, or gonapophyses—a dorsal, a ventral and an inner pair. The two inner valves form a channel through which the eggs are conveyed. In Locustide (Fig. 79) the three f9 ENTOMOLOGY valves of each side are held together by tongues and grooves, which, how- Cc ever, permit sliding movements to take place. Most authorities have found that the gonapophyses belong to the segmental series of paired appendages Cross section of the 7 | i athaoeeal d ovipositor of Sirer. c, are homodynamous with limbs—an channel; d, d, dorsal pertain commonly to abdominal segments valves; 4%, united inner : 7 valves: vy) a, wentrale | SEVEN, Clo mieaniceaiiae: Monica aa sas The ovipositor attains its greatest complexity in Hymenoptera, in which it becomes modified tor sawing, boring or sting- meen lin Sires (RI1e 580) the inner valves are united together; in Apis the dorsal valves are rep- d d T'tc. 82. Sting of honey bee. A, 17, 2, 3, positions in three successive thrusts; s, sheath. B, cross section; c, channel; 7, united inner valves, forming the sheath; wv, wv, ventral valves, or darts.—A, after CHESHIRE; B, after FENGER. resented by a pair of palpi, the inner valves unite to form the sheath (Fig. 81, B), and the ven- tral two form the darts, each of Sting and poison apparatus which has ten barbed teeth behind of honey bee. ag, accessory : ; gland: >, palpus; pz, poison ItS apex,” which tend eto aremeer gland (formic acid); 7, teser- the withdrawal of the seme umommea voir; s, sting.—After KRaAEPE- LIN. wound. The action of the sting, as ANATOMY AND PHYSIOLOGY 71 described by Cheshire, is rather complex. serves to open a wound and to guide the darts; these strike in alternately, inter- rupted at intervals by the deeper plung- menor tae sheath (Fig. 81, A). The poison of the honey bee is secreted by two glands, one acid and the other alka- line. The former (Fig. 82) consists of a glandular region which secretes formic acid, of a reservoir, and a duct that empties its contents into the channel of the sheath. The alkaline gland also opens into the reservoir. It is said that both fluids are necessary for a deadly effect; and that in insects which simply paralyze their prey, as the solitary wasps, the alkaline glands are functionless. Male Genitalia.—The penis may be hollow or else solid, and in the latter case the contents of the ejaculatory duct are spread upon its surface. Fic. 84. female. Extremity of abdomen of a male May fly, Hexagenia varia- bilis, ventral aspect. c, c, ¢, cerci; cl, cl, claspers; 1, 1, in- tromittent organs. Briefly, the sheath Extremity of abdomen of a male beetle, Hy- drophilus, ventral aspect. g, genitalia; p, penis; vi, v®, pairs of valves enclosing the penis; 6-0, sterna of abdominal seg- ments.—After KoLse. Morphologically, the male gona- pophyses correspond to those of the Ther pens (Biss Sa); rep- resents the two inner valves of the ovipositor and is frequently enclosed by one or two pairs of valves. In Ephemerida the two inner valves are partly or entirely separate from each other, forming two intromit- tent organs (Fig. 84). In male Odonata, the ejaculatory duct opens on the ninth abdominal segment, but the copulatory organ is placed on the under side of the sec- ond segment, to which the spermato- zoa are transferred by the bending of the abdomen. At copulation, the abdominal claspers of the ie ENTOMOLOGY male grasp the neck of the female, and the latter bends her abdomen forward until the tip reaches the peculiar copulatory apparatus of the male. Fig. 85. Genitalia of a moth, Samia cecropia. A, male; B, female; a, anus; c, c, claspers; 0, opening of common oviduct; p, penis; s, uncus (the doubly hooked organ); wv, vesti- bule, into which the vagina opens. The numbers refer to abdominal segments. The claspers of the male consist of a single pair, variously formed. They are present in Ephemerida, Neuroptera, Tri- choptera, Lepidoptera (Fig. 85), Diptera and some Hymen- optera, though not in Coleoptera, and often afford good spe- cific characters, as in Odonata. In butterflies of the genus Fic. 86. Terminal abdominal appendages of a dragon fly, Plathemis trimaculata. A, male; B, female. i, inferior appendage; s, s, superior appendages (cerci). The numbers refer to abdominal segments. Thanaos, the claspers are peculiar in being strongly asym- metrical. In Odonata (Fig. 86, 4) and Orthoptera, (Fig. 87, A) the cerci of the male often serve as claspers. ANATOMY AND PHYSIOLOGY 73 In many insects the tergum of the dast abdominal segment forms a small suranal plate (Fig. 87, B, sp); this sometimes Fic. 87. Extremity of the abdomen of a grasshopper, Melanoplus differentialis. A, male; B, female. The terga and sterna are numbered. c, cercus; d, dorsal valves of ovi- positor; e, egg guide; p, podical plate; s, spiracle; sp, suranal plate; v, ventral valves of ovipositor. supplements the claspers of the male in their function, as in Lepidoptera (Fig. 85, A, s). 2. INTEGUMENT Insects excel all other animals in respect to adaptive modi- fications of the integument. No longer a simple limiting membrane, the integument has become hardened into an exter- nal skeleton, evaginated to form manifold adaptive structures such as hairs and scales, and invaginated, along with the un- derlying cellular layer, to make glands of various kinds. Chitin.—The skin, or cuticula, of an insect differs from that of a worm, for example, in being thoroughly permeated with a peculiar substance known as chitin—the basis of the arthropod skeleton. This is a substance of remarkable sta- bility, for it is unaffected by almost all ordinary acids and alkalies, though it is soluble in sodic or potassic hypochlorite (respectively, Eau de Labarraque and Eau de Javelle) and yields to boiling sulphuric acid. If kept for a year or so under water, however, chitin undergoes a slow dissolution, *The cuticula of an insect should be distinguished from the cuticle of a vertebrate, the former being a hardened fluid, while the latter consists of cells themselves, in a dead and flattened condition. 74 ENTOMOLOGY possibly a putrefaction, which accounts in a measure for the rapid disappearance of insect skeletons in the soil (Miall and Denny). By boiling the skin of an insect in potassic hydrate it is possible to dissolve away the cuticular framework, leav- ing fairly pure chitin, without destroying the organized form of the integument, though less than half the weight of the integument is due to chitin. The formula of chitin is given as C,H,,NO, or C,,H,,NO,,. by Krukenberg, and Packie adopts the formula C,;H,,N.O,,; though no two chemists agree as to the exact proportions of these elements, owing probably to variations in the substance itself in different in- sects or even in the same species of insect. Iron, manganese and certain pigments also enter into the composition of the integument. Chitin is not peculiar to ar- thropods, for it has been de- tected in the sete and pharyn- Section through integument of a geal teeth of annelid worms, beetle, Chrysobothris. b, bas t c * SHR ee mie ‘i. 2 the shell of Lingula and the membrane; c!, primary cuticula; c?, secondary cuticula; 1, hypodermis cell; pen of the cuttle fish (Kruken- n, nucleus.—After Tower. 4 berg). The chitinous integument (Fig. 88) of most insects con- sists of two layers: (1) an outer layer, homogeneous, dense, without lamella or pore canals, and being the seat of the cutic- ular colors; (2) an inner layer, “thickly pierced with pore canals, and always in layers of different refractive indices and different stainability.”” (Tower.) These two layers, respec- tively primary and secondary cuticula, are radically different in chemical and physical properties. The chitinous cuticula is secreted, as a fluid, from the hypodermis cells. Each layer arises as a fluid secretion from the hypodermis cells, the pri- mary cuticula being the first to form and harden. The fluid that separates the old from the new cuticula at hd ANATOMY AND PHYSIOLOGY 75 ecdysis is poured over the hypodermis by certain large special cells, which, according to Tower, “are not true glands, but the setigerous cells which, in early life, are chiefly concerned with the formation of the hairs upon the body; but upon the Fic. 89. Modifications of the hairs of bees. A, B, Megachile; C, E, F, Colletes; D, Chelostoma.—After SAUNDERS. loss of these, the cell takes on the function of secreting the exuvial fluid, which is most copious at pupation. These cells degenerate in the pupa, and take no part in the formation of the imaginal ornamentation.” Histology.—The chitinous cuticula owes its existence to the activity of the underlying layer of hypodermus cells (Fig. 88). These cells, distinct in embryonic and often in early lar- val life, subsequently become confluent by the disappearance of the intervening cell walls, though each cell is still indicated by its nucleus. The cells are limited outwardly by the cuticula and inwardly by a delicate, hyaline basement membrane; they contain pigment granules, fat-drops, etc. Externally the cuticula may be smooth, wrinkled, striate, granulate, tuberculate, or sculptured in numberless other Ways; it may be shaped into all manner of structures, some of which are clearly adaptive, while others are unintelligible. 76 ENTOMOLOGY Hairs, Sete and Spines.—These occur universally, serv- ing a great variety of purposes; they are not always simple in form, but are often toothed, branched or otherwise modified (Fig. 89). Hairs and bris- tles are frequently tactile in function, over the general integument or else FIG. 90. locally ; or olfactory, as on the antennze of moths; or occasionally auditory, as on the antennz of the male mosquito; these and other sensory modifications are described beyond. The hairy clothing of some hibernating cater- pillars (as [sia isabella) probably pro- Section of antenna of a moth) Saturnia, to show tects them .from sudden chamseumes developing hairs. c, cutic- temperature. Hairs and spines fre- ula; .f, formative cell of : b ; hair; h, hypodermis; ¢ qQuently protect an insect from its ene- trachea.—After SEMPER. : : mies, especially when these structures are glandular and emit a : Fic. Ol. malodorous, nauseous or e irritant fluid. Glandular hairs on the pulvilli of many ies, “beetles, “ete: enable these insects to walk on slippery surfaces. The twisted or branched hairs Oi bees “seve to Veather and hold pollen grains; in short, these simple struc- tures exhibit a surprising variety of adaptive modifica- J hy Radial section through the base of a hair of a caterpillar, Pieris rape. c, cutic- other subjects. ula; f, formative cell; h, hair; hy, hypo- dermis. tions, many of which will be described in connection with A» ait arises irompra modified hypodermis cell (Fig. 90), the contents of which ANATOMY AND PHYSIOLOGY uf extend through a pore canal into the interior of the hair (Fig. QI); sometimes, to be sure, as in glandular or sensory hairs, the hair cell is multinucleate, rep- resenting, therefore, as many cells aseunere are nuclei. The wall of a hair 1s continuous with the gen- eral cuticula and at moulting each hair is stripped off with the rest of the cuticula, leaving in its place a new hair, which has been form- ing inside the old one. Scales. — Besides occurring throughout the order Lepidoptera and in numerous’ Trichoptera, § scales are found in many Thys- anura and Collembola, several | families of Coleoptera (including Dermestidze and Curculionide), a few Diptera and a few Psocide. Though diverse in form (Fig. 92), scales are essentially flattened sacs having at one end a short pedicel for attachment to the in- Various forms. of _ scales. A, E, thysanuran, Machilis; B, beetle, Anthrenus; C, butterfly, Pieris; D, moth, Limacodes. tegument. The scales usually bear markings, which are more or less characteristic of the species; these markings, always minute, are in some species so exquisitely fine as to test the highest powers of the microscope; the scales of certain Collembola (Lepi- Ba Nee: docyrtus, etc.) have long been used, under the name _ of * Pedura”* scales, to test -the Cross section of scale of Anosia.— resolving power of objec- After MAyEr. tives, for which purpose they are excelled only by some of the diatoms. Butterfly scales are marked with parallel longitudinal ridges (Mig. 92, C), which are confined almost entirely to the upper, or ex- 78 ENTOMOLOGY posed, surface of the scale (Fig. 93) and number from 33 or less (Anosia) to 1,400 (Morpho) to each scale, the strie being from .002 mm. to .0007 mm. apart (Kel- loge); between these longi- tudinal ridges may be dis- cerned delicate transverse markings. Internally, scales are hollow and often contain pigments derived from the blood. On the wing of a butter- fly the scales are arranged in regular rows and overlap one another, as in Fig. 94; in the more primitive moths and in Trichoptera, how- Arrangement of scales on the wing of a ever, their distribution 1S butterfly, Papilio. Fic. 94. rather irregular. A scale is the equivalent of a hair, for (1) a complete series of transitions from hairs to scales may be found on a single individual (Fig. 95);and (2) hairs and scales agree in their manner of development, as shown by Semper, Schaffer, Spu- GsO5: : \ \) \ | | \ b ? \} a e ; g hy : j k ! a c \ Hairs and scales of a moth, Samia cecropia. ler, Mayer and others. Both hairs and scales arise as pro- cesses from enlarged hypodermis cells, or formative cells (Fig. 96). The scale at first contains protoplasm, which gradually withdraws, leaving short chitinous strands to hold the two membranes of the scale together. ANATOMY AND PHYSIOLOGY 79 Uses of Scales.—Among Thysanura and Collembola, scales occur only on such species as live in comparatively dry situa- tions, from which it may be inferred that the scales serve to retard the evaporation of moisture through the delicate integu- ment of these insects. This inference is supported by the fact FTG GO: Development of butterfly scales. Androconia of butter- A, Vanessa; B, Anosia. b, base- flies. A, Pieris rape; B, ment membrane; f, formative cell; . Everes comyntas. h, hypodermis; s, scale.—After Mayer. that none of the scaleless Collembola can live long in a dry atmosphere; they soon shrivel and die even under conditions of dryness which the scaled species are able to withstand. In Lepidoptera the scales are possibly of some value as a mechan- ical protection; they have no influence upon flight, as Mayer has proved, and appear to be useful chiefly as a basis for the So ENTOMOLOGY development of color and color patterns—which are not infre- quently adaptive. Androconia.—The males of many butterflies, and the males only, have peculiarly shaped scales known as androcoma (Fig. 97); these are commonly confined to the upper surfaces of the front wings, where they are mingled with the ordinary scales or else are disposed in special patches or under a fold of the costal margin of the wing (Thanaos). he characteris- tic oders of male butterflies have long been attributed to é these androconia and M. B. ays Thomas has found that the aN scales arise from glandular cells, which doubtless secrete a fluid that emanates from the scale as an odorous va- por, the evaporation of the fluid being facilitated by the Fie. 08. IM) welll) aa NY aN Section across tarsus of a beetle, Hylobius, to show bulbous glandular spreading or branching form en nes of the androconium. Similar scales occur also on the wings of various moths and some Trichoptera (Mystacides). Glands.—A great many glands of various form and func- tion have been found in insects. Most of these, being formed from the hypodermis, may logically be considered here, ex- cepting some which are intimately concerned with digestion or reproduction. Glandular Hairs and Spines.—The presence of adhesive hairs on the empodium of the foot of a fly enables the insect to walk on a smooth surface and to wall upside down; these tenent hairs emit a transparent sticky fluid through minute pore canals in their apices. The tenent hairs of Hylobius (Fig. 98) are each supplied with a flask-shaped unicellular gland, the glutinous secretion of which issues from the bulbous ANATOMY AND PHYSIOLOGY SI extremity of the hair. Bulbous tenent hairs occur also on the tarsi of Collembola, Aphididz and other insects. Nettling hairs or spines clothe the ; i : ie Fic. 99. caterpillars of ‘certain Saturniidz (Automeris), Liparidz, etc. These spines (Fig. 99), which are sharp, brittle and filled with poison, break to pieces when the insect 1s handled and cause a cutaneous irritation h much like that made by nettles. In Lagoa crispata (Fig. 100) the irri- tating fluid is secreted, as is usual, by several large hypodermal cells Beatie. base of each spme. ‘hese irritating hairs protect their pos- sessors from almost all birds except g,... tinging hair of a caterpillar, cuckoos. Gastropacha. c, cuticula; g, care * gland cell; hf, hair; hy, hypo- Repetlent Glands.—The various Gemmis.-Aftes Coats. offensive fluids emitted by insects are also a highly effective means of defence against birds Co aaa, > and other insectivorous vertebrates as well as against preda- ceous insects. The blood itself serves as a repellent fluid in the oil-beetles (Meloide) and Coccinellide, issuing as a yellow fluid from a pore at the end of the femur. The blood of Meloide (one species of which is still used me- dicinally under the name of “ Spanish Fly”) contains cantharidine, an ex- Fic. 100. tremely caustic substance, which is an almost perfect protection against birds, reptiles and predaceous insects. Coccinel- Stinging spines of a lide and Lampyridz are similarly exempt psereula, “Logon ert trom attack. Lafve of Cimbex when pata.—After PacKarp. : 2 : : : disturbed squirt jets of a watery fluid from glands opening above the spiracles. Many Carabidee eject a pungent and often corrosive fluid from a pair of anal 7 82 EN TOMOLOGY glands (Fig. 146); this fluid in Brachinus, and occasionally in Galerita janus and a few other carabids, volatilizes explo- sively upon contact with the air. When one of these “ bom- bardier-beetles ” 1s molested it discharges a puff of vapor, accompanied by a distinct report, reminding one of a minia- ture cannon, and this performance may be repeated several times in rapid succession; the vapor is acid and corrosive, staining the human skin a rust-red color. FIG) ton, Individuals of a large South American Brachinus when seized ‘“* immediately began to play off their artillery, burning and staining the flesh to such a degree that only a few specimens could be cap- tured with the naked hand, leaving a mark which remained for a considerable time.” (Westwood.) As malodorous insects, Hemiptera are Osmeterium of Papilio notorious, though not a few hemipte- He a rous odors are (apart from their associa- tions) rather agreeable to the human olfactory sense. Com- monly the odor is due to a fluid from a mesothoracic gland or glands, opening between the hind coxe. Eversible hypodermal glands of many kinds are common in larvee of Coleoptera and Lepidoptera. The larve of Melasoma lapponica, among other Chrysomelide, evert numerous paired vesicles which emit a peculiar odor. The caterpillars of our Papilio butterflies, upon being irritated, evert from the pro- thorax a yellow Y-shaped osmeterium (Fig. 101) which dif- fuses a characteristic but indescribable odor that is probably repellent. The larva of Cerura everts a curious spraying apparatus from the under side of the neck. Alluring Glands.—Odors are largely used among insects to attract the opposite sex. The androconia of male butterflies have already been spoken of. Males of Catocala concumbens disseminate an alluring odor from scent tufts on the middle legs. Female saturniid moths (as cecropia and promethea) ANATOMY AND PHYSIOLOGY 83 entice the males by means of a characteristic odor, emanating from the extremity of the abdomen. In lycznid caterpillars, an eversible sac on the dorsum of the seventh abdominal seg- ment secretes a sweet fluid, for the sake of which these larve are sought out by ants. Wax Glands.— Wax is secreted by. insects of several orders, but especially Hymenoptera and Hemiptera. In the worker Ventral aspect of worker honey bee, showing the four pairs of wax scales.—After CHESHIRE. honey bee the wax exudes from unicellular hypodermal glands and appears on the under side of the abdomen as four pairs of wax scales (Fig. 102). Plant lice of the genus Schizo- neura owe their woolly appearance to dense white filaments of wax, which arise from glandular hypodermal cells. In scale insects, waxen threads, emerging from cuticular pores, become matted together to form a continuous shield over and often under the insect itself, the cast skins often being incorporated into this waxen scale. The wax glands in Coccidz are simply enlarged hypodermis cells. Silkk Glands.—Larve of very diverse orders spin silk, for the purpose of making cocoons, webs, cases, and supports of one kind or another. Silk glands, though most characteristic of Lepidoptera and Trichoptera, occur also in the cocoon- spinning larve of not a few Hymenoptera (saw flies, ichneu- mons, wasps, bees, etc.), in Diptera (Cecidomyiide), Neurop- 84 ENTOMOLOGY tera (Chrysopide, Myrmeleonide), and in various larvee whose pup are suspended from a silken support, as in the coleopterous families Coc- cinellidee and Chrysomel- idze (in part) and the dip- terous family Syrphide, as well as most diurnal Lepidoptera. Fic. 104. Head of caterpillar of Samia cecropia. a, antenna; c, clypeus; /, labrum; /p, labial palpus; m, mandible; mp, maxillary palpi; o, ocelli; s, spinneret. The silk glands of caterpillars are homologous with the true salivary glands of other insects, opening as usual through the hy- popharynx, which is modified to form a spinning organ, or spin- neret (Fig. 103). ‘The silk glands of Lepidoptera are a pair of long tubes, one on each side of the body, but often much longer than the body and consequently convo- luted. Thus in the silk worm. (Bombyx mori) they are from four to five times as long as the Silk glands of the silk worm, one : aA B X Bombyx mori. cd, common duct; body and*in Telea polyphemus, 4 one of ine paced dagen seven times as long. In the silk Filippi’s glands; gi, gland proper; =, p, thread press; 7, reservoir. worm the convoluted glandular portion of each tube (Fig. 104) opens into a dilatation, or silk reservoir, which in turn empties into a slender duct, and the ANATOMY AND PHYSIOLOGY 85 two ducts join into a short common duct, which passes through the tubular spinneret. Two divisions of the spinning tube are distinguished: (1) a posterior muscular portion, or thread-press and (2) an anterior directing tube. The thread- press combines the two streams of silk fluid into one, determines the form of the silken thread and arrests the emission of the thread at times, besides having other functions. The silk fluid hardens rapidly upon exposure to the air; about fifty per cent. of the fluid is actual silk substance and the re- mainder consists of protoplasm and gum, with traces of wax, pigment, fat and resin. A transverse or radial section of a Fic. I05. silk gland shows a layer of glandular epithelial cells, with the usual intima and basement membrane (Fig. 105) ; the cells are remarkably large and their nuclei are often branched; the intima is distinctly striated, from the presence : 5 2 Fa Alte tee of pore canals. The glands arise as cate eae evaginations of the pharynx (ectoder- the silk, worm. 4, radial; mal di fits Sas ag -] B, transverse. 6b, basement jeanG the chitinous intuma of each jocprane: intimac & PlamG@nsieast at each moult; alone with s!ndularcell with branched nucleus.—After HELM. A i the general integument. The silk glands of Trichoptera are essentially like those of Lepidoptera, but the glands of Chrysopa, Myrmeleon, Coc- cinellidee, Chrysomelide and Syrphidze, which open into the rectum, are morphologically quite different from those of Lepidoptera. 3. MUSCULAR SYSTEM The number of muscles possessed by an insect is surpris- ingly large. A caterpillar, for example, has about two thousand. 86 ENTOMOLOGY The muscles of the trunk are segmentally arranged—most evidently so in the body of a larva or the abdomen of an imago, where the musculature is essentially the same in sev- eral successive segments. In the thoracic segments of an ima- go, however, the musculature is, at first sight, unlike that of Fic. 106. Muscles of cockroach; of ventral, dorsal and lateral walls, respectively. a, alary muscle; abc, abductor of coxa; adc, adductor of coxa: ef, extensor of femur; h, head muscles; /s, longitudinal sternal; /t, longitudinal tergal; /th, lateral thoracic; os, oblique sternal; of, oblique tergal; ts, tergo-sternal; ts!, first tergo-sternal.—After Mratt and DEnNNy. the abdomen, and in the head it is decidedly different ; though future studies will doubtless show that the thoracic and cepha- lic kinds of musculature are only modifications of the simpler abdominal type—modifications brought about in relation to the needs of the legs, wings, mouth parts, antennze and other movable structures. The muscular system has been generally neglected by stu- dents of insect anatomy; the only comprehensive studies upon the subject being those of Straus-Durckheim (1828) on the beetle Melolontha; Lyonet (1762), Newport (1834) and Lubbock (1859) on caterpillars; and the more recent studies of Lubbock and Janet on Hymenoptera. ANATOMY AND PHYSIOLOGY The more important muscles in the body of a cockroach are represented in Figs. 106-108, from Muall longitudinal sternals with the longitudinal scope the abdominal segments; the oblique sternals bend the abdomen laterally; the tergo-sternals, or vertical expiratory mus- cles, draw the tergum and sternum to- gether. The muscles of the legs and the wings have already been referred to. Structure of Muscles.—The muscles of insects differ greatly in form and are inserted frequently by means of chitinous tendons. A muscle is a bundle of long fibers, each of which has an outer elastic membrane, or sarcolemma, within which The tergals act. to tele- and Denny. Fic. 100. Striated muscle fiber of an insect. are several nuclei; thus the fiber represents several cells, which have become confluent. With rare exceptions (“alary ” muscles and possibly a few thoracic muscles) the muscle ErGeeuno: LK MD nl Minute structure of a striated muscle fiber. A, longitudinal section; B, trans- verse section in the region of /; C, trans- verse section in the region of n. lI, longitudinal fibrille; mn, MWKrause’s mem- brane; n/, nucleus; r, radial fibrille; s, sarcolemma.—After JANET. fibers of an insect present a striated appearance, owing to alternate light and dark bands (Fig. 109), the for- mer being singly refracting, or isotropic, and the latter doubly refracting, or aniso- tropic. The these fibers, being extremely difficult of has given rise to much dif- ference of he most plausible view is that of Janet minute structure of interpretation, opinion. van Gehuchten, and others, who hold that both kinds of dark bands (Fig T10) consist of highly elastic threads of spongioplasm (aniso- tropic) embedded in a matrix of clear, semi-fluid, nutritive 88 ENTOMOLOGY hyaloplasm (isotropic). The spongioplasmic threads of the long bands extend longitudinally and those of the short bands (“ Krause’s membrane”) radially, in respect to the form of the fiber. Moreover, the attenuated extremities of the longi- tudinal fibrillae connect with the radial fibrilla, the points of connection being marked by slight thickenings, or nodes, which go to make up Krause’s membrane. Under nervous stimulus a muscle shortens and thickens because its component fibers do, and this in turn is attributed to the shortening and thickening of the longitudinal fibrillz. When the stimulus ceases, the radial fibrilla, by their elas- ticity, possibly pull the longitudinal ones back into place. The last word has not been said, however, upon this perplexing subject. Muscular Power.—The muscular exploits of insects appear to be marvellous beside those of larger animals, though they are often exaggerated in popular writings. The weakest in- sects, according to Plateau, can pull five times their own weight and the average insect, over twenty times its weight, while Donacia (Chrysomelidz) can pull 42.7 times its weight. As contrasted with these feats, a man can pull in the same fashion but .86 of his weight and a horse from .5 to .83. How are these differences explained ? It 1s incorrect to say that the muscles of insects are stronger than those of vertebrates, for, as a matter of fact, the contrac- tile force of a vertebrate muscle is greater than that of an insect muscle, other things being equal. The apparently greater strength of an insect in proportion to its weight is accounted for in several ways. ‘The specific gravity of chitin is less than that of bone, though it varies greatly in both sub- stances. Furthermore, the external skeleton permits muscu- lar attachments of the most advantageous kind as compared with the internal skeleton, so that the muscles of insects sur- pass those of vertebrates as regards leverage. These reasons are only of minor importance, however. Small animals in general appear to be stronger than larger animals (allowing (0/6) ANATOMY AND PHYSIOLOGY 9 for the differences in weight) for the same reason that a smaller insect has more conspicuous strength than a larger one, when the two are similar in everything except weight. For example: where a bumble bee can pull 16.1 times its own weight, a honey bee can pull 20.2; and where the same bumble bee can carry while flying a load 0.63 of its own weight, the honey bee can carry 0.78. Always, as Plateau has shown, the lighter of two insects is the stronger in respect to external manifestations of muscular force—in the ratio of this muscu- lar strength to its own weight. To understand this, let us assume that a beetle continues to grow (as never happens, of course). As its weight is increas- ing so is its strength—but not in the same proportion. For while the weight—say that of a muscle—increases as the cube of a single dimension, the strength of the muscle (depending solely upon the area of its cross section) 1s increasing only as the square of one dimension—its diameter. ‘Therefore the increase in strength lags behind that of weight more and more; consequently more and more strength is required sim- ply to move the insect itself, and less and less surplus strength remains for carrying additional weight. Thus the larger in- sect is apparently the weaker, though it is actually the stronger, in that its total muscular force is greater. The writer uses this explanation to account also for the inability of certain large beetles and other insects to use their wings, though these organs are well developed. Increasing weight (due to a larger supply of reserve food accumulated by the larva) has made such demands upon the muscular power that insufficient strength remains for the purpose of flight. Statements such as this are often seen—a flea can jump a meter, or six hundred times its own length. Almost needless to say, the length of the body is no criterion of the muscular power of an animal. 4. NERVOUS SYSTEM The central nervous system extends along the median line of the floor of the body as a series of ganglia connected by gO JEG, GEE Central system of a thysanuran, Machilis. The thoracic and abdom- inal ganglia are numbered antennal nervous in succession. 4, EN TOMOLOGY nerve cords. glion (double in origin) for each primary segment, and the connecting cords, or Typically, there is a gan- commissures, are paired; these conditions are most nearly realized in embryos and in the most generalized insects—Thysa- nura (Fig. rir). In all adult imsects however, the originally separate ganglia consolidate more or less (Fig. 112) and frequently unite to the commiussures form single cords. Thus in Tabanus (Fig. 112, C) the three thogacieveeu. glia have united into a single com- pound ganglion and the abdominal gan- glia are concentrated in the anterior part of the abdomen; in the grasshop- per, the nerve cord, double in the tho- rax, is single in the abdomen. Various other modifications of the same nature occur. Cephalic Ganglia.—In the head the primitive ganglia always unite to form two namely the brain and the subewsophageal ganglion (disregarding a few anomalous cases the latter -is> saicdiitormbe compound ganglia, in which absent ). The brain, or suprawsophageal gan- glion (Fig. 113), is formed by the union of three primitive ganglia, or meuromeres (Fig. 55), namely, (1) the protocere- brum, which gives off the pair of optic nerves; (2) the deutocerebrum, which nerve; b, brain; e, compound eye; /, labial nerve; m, mandibular nerve; maxillary nerve; 0, cesophagus; ol, optic lobe; s, subcesophageal ganglion; sy, sympathetic nerve.—After OUDEMANS. mx, ANATOMY AND PHYSIOLOGY gl innervates the antennz; and (3) the fritocerebrum, which in Apterygota bears a pair of rudimentary appendages that are regarded as traces of a second pair of antenne. Successive stages in the concentration of the central nervous system of Diptera. 4A, Chironomus; B, Empis; C, Tabanus; D, Sarcophaga.—After Branprt. “Mes § YS Vig Z Sl IIT m= Nervous system of the head of a cockroach. a, antennal nerve; ag, anterior lateral ganglion of sympathetic system; b, brain; d, salivary duct; f, frontal ganglion; h, hypo- pharynx; 7, labrum; /i, labium; m, mandibular nerve; mx, maxillary nerve; n/, nerve to labrum; n/i, nerve to labium; 0, optic nerve; oc, cesophageal commissure; oe, cesophagus; bg, posterior lateral ganglion of sympathetic system; r, recurrent nerve of sympa- thetic system; s, subcesophageal ganglion.—After Horer. The subcesophageal ganglion (Fig. 113) is always con- nected with the brain by a pair of nerve cords (@sophageal g2 commissures) between which the cesophagus passes. EN TOMOLOGY This compound ganglion represents at most four neuromeres: (1) mandibular, innervating the mandibles; Sympathetic nervous system of an insect, diagrammatically represented. a, antenna! nerve; b, brain; f, frontal ganglion; 7, J, paired lateral ganglia; m, mouth parts; o, 7, recurrent nerve; Ss, nerve to salivary glands; st, stomachic ganglion.—After KoLBe. nerves to upper optic nerve; (2) superlingual, found by the author in Collembola, but not yet reported in the less gen- eralized insects; (3) maxillary, inner- vating the maxilla; (4) labial, which sends a pair of nerves to the labium. The minute structure of the brain, though highly complex, has received considerable study, but will not be described here for the reason that the anatomical facts are of no general interest so long as their physiological interpretation remains obscure. Sympathetic System.—Lying along the median dorsal line ofthe cesophagusys a reeurrent, or ‘stomato- ee arises anteriorly in a frontal gan- gastric, nerve }(Fig. which glion and terminates posteriorly in situated at the anterior end of the mid intes- the recurrent nerve are two pairs of lateral ganglia, © a stomachic ganglion tine. Connected with the anterior of which innervate the dorsal vessel and the posterior, the tracheze of the head: The *veamal nerve cord may include also a median nerve thread (Fig. 111) which gives off paired transverse nerves to the muscles of the spiracles. Structure of Ganglia and Nerves.—A ganglion consists of (1) a dense cortex, composed of ganglion cells (Fig. 115), each of which has a large rounded nucleus and gives off usu- ally a single nerve fiber; and (2) a clear medullary portion ANATOMY AN)D PHYSIOLOGY 93 (Punktsubstanz) derived from the processes of the cortical ganglion cells and serving as the place of origin of nerve fibril- le. There are, however, ganglion cells from which processes may pass directly into nerve fibrillz. A nerve, in an insect, consists of an axis-cylinder, composed of fibrillae, and an enveloping membrane, or neurilemma. The axis-cylinder is the transmitting portion and the ganglia are Fic. 115. Transverse section of an abdominal ganglion of a caterpillar. a, axis-cylinder; g, ganglion cells; , neurilemma; p, Punktsubstanz. the trophic centers, 1. e., they regulate nutrition. A nerve is always either sensory, transmitting impulses inward from a sense organ; or else motor, conveying stimuli from the central nervous system outward to muscles, glands, or other organs. Functions.—The brain innervates the chief sensory organs (eyes and antennz) and converts the sensory stimuli that it receives into motor stimuli, which effect co-ordinated muscular or other movements in response to particular sensations from the environment. The brain is the seat of the will, using the term “ will” in a loose sense; it directs locomotor movements of the legs and wings. An insect deprived of its brain cannot go to its food, though it is able to eat if food be placed in con- tact with the end-organs of taste, as those of the palpi; further- more, it walks or flies in an erratic manner, indicating a lack of co-ordination of muscular action. The subcesophageal ganglion controls the mouth parts, co- ordinating their movements as well as some of the bodily movements. 94 ENTOMOLOGY The thoracic ganglia govern the appendages of their respec- tive segments. These ganglia and those of the abdomen are to a great extent independent of brain control, each of these ganglia being an individual motor center for its particular segment. Thus decapitated insects are still able to breathe, walk or fly, and often retain for several days some power of movement. . In regard to the sympathetic system, it has been shown ex- perimentally that the frontal ganglion controls the swallowing movements and exerts through the stomatogastric nerve a regulative action upon digestion. The dorsal sympathetic sys- tem controls the dorsal vessel and the salivary glands, while the ventral sympathetic system is concerned with the spiracu- lar muscles. 5. SENSE ORGANS For the reception of sensory impressions from the external world, the armor-like integument of insects is modified in a great variety of ways. Though sense organs of one kind or another may occur on almost any part of an insect, they are most numerous and varied upon the head and its appendages, particularly the antenne. Antennal Sensilla——Some idea of the diversity of form in antennal sense organs may be obtained from Figs. 116-125, taken from a recent paper by Schenk, whose useful classifica- tion of antennal sensilla, or sense organs, is here outlined: t. Sensillum celoconicum—a conical or peg-like projection immersed in a pit (Figs. 116-117). In all probability olfactory. 2. S. basiconicum—a cone projecting above the general sur- face (Fig. 118). Probably olfactory. 3. S. styloconicum—a terminal tooth or peg seated upon a more or less conical base (Fig. 119). Olfactory. 4. S. cheticum—a bristle-like sense organ (Fig. 120). Tactile. 5. S. trichodeum Tactile. a hair-like sense organ (Figs. 121, 122). ANATOMY ANT) PHYSIOLOGY 95 6. S. placodeum—a membranous plate, its outer surface continuous with the general integument (Fig. 123). Func- Fics. 116-125. Types of antennal sensilla, in longitudinal section (excepting Figs. 119 and 120). Fig. 116, sensillum cceloconicum; 117, cceloconicum; 118, basiconicum; 119, stylo- conicum; 120, cheticum; 121, trichodeum; 122, trichodeum; 123, placodeum; 124, ampullaceum; 125, ampullaceum; c, cuticula; ji, hypodermis; m, nerve; s, sensory cell. Figs. 116, 118, 121, 123, 124, honey bee, Apis mellifera; 117, 119, 122, moth, Fidonia piniaria; 120, moth, Ino pruni; 125, wasp, Vespa crabro.—After SCHENK. 96 ENTOMOLOGY tion doubtful ; not auditory and probably not olfactory, though the function is doubtless a mechanical one; Schenk suggests that they are affected by air pressure, as when a bee or wasp is moving about in a confined space. 7. S. ampullaceum—a more or less flask-shaped cavity with an axial rod (Figs. 124, 125). Probably auditory. These types of sensilla will be referred to in physiological order. Touch.—The tactile sense is highly developed in insects, and end-organs of touch, unlike those of other senses, are com- monly distributed over the entire integument, though the an- tennz, palpi and cerci are especially sensitive to tactile impres- sions. The end-organs of touch are bristles (sensilla chzetica) or hairs (sensilla trichodea), each arising from a special hypo- dermis cell and having connection with a nerve. Sensilla . cheetica doubtless receive impressions from foreign bodies, while sensilla trichodea, being best developed in the swiftest flying insects and least so in the sedentary forms, may be affected by the resistance of the air, when the insect or the air itself 1s in motion. Not all the hairs of an insect are sensory, however, for many of them have no nerve connections. In blind cave insects the antennz are very long and are ex- quisitely sensitive to tactile impressions. Taste.—The gustatory sense is unquestionably present in insects, as is shown both by common observation and by pre- cise experimentation. Will fed wasps with sugar and then replaced it with powdered alum, which the wasps unsuspect- ingly tried but soon rejected, cleaning the tongue with the fore feet in a comical manner and manifesting other signs of what we may call disgust. Forel offered ants honey mixed with morphine or strychnine; the ants began to feed but at once rejected the mixture. In its range, however, the gusta- tory sense of insects differs often from that of man. Thus Will found that Hymenoptera refused honey with which a ANATOMY AND PHYSIOLOGY 97 very little glycerine had been mixed (though Muscidz did not object to the glycerine) and Forel found that ants ate unsus- Fic. 126. c ( \s Section through tongue of wasp, Vespa vulgaris. c, cuticula; g, gland cell; h, hypodermis; ”, nerve; ob, gustatory bristle; ph, protecting hair; sc, sensory cell; tb, tactile bristle—After WILL. pectingly a mixture of honey and phosphorus until some of them were killed by it. Under the same circumstances, man would be able to detect the phosphorus but not the glycerine. Location of Gustatory Organs.— nn which the pigment in the form of WH" ° fine black granules is contained chiefly in short cells that surround wires . : Portion of compound eye of the retinula distally; and an inner fy, Calliphora vomitoria, radial section. c, cornea; 1%, iris pig- ment; n, nerve fibers; mc, nerve zone of retinal pigment, in which Giempicment cells are long and ccllsi 7, retinal plement, 7, tra: Ss chea.—After Hicxson. slender, and enclose the retinula proximally. All these parts are hypodermal in origin, as is also the fenestrate basement membrane, through which pass tracheze and nerve fibers. The nerve fibrille, which are ultimate branches of the optic nerve, pass into the retinal cells—the end- organs of vision. Under the basement membrane is a fibrous optic tract of complex structure. Physiology.—After much experimentation and discussion upon the physiology of the compound eye—the subject of the monumental works of Grenacher and Exner—Muller’s “* mo- saic” theory is still generally accepted, though it was proposed early in the last century. It is thought that an image is formed by thousands of separate points of light, each of which corresponds to a distinct field of vision in the external world. I12 ommatid- vomuitoria. A, radial section (chiefly); B, transverse section through middle region; C, transverse section through basal region; bm, basement membrane; c, cornea; ”, nucleus; nv, nerve fibrille; pc, pseudocone; pg’, pg’, cells containing iris pig- ment; pg*, cell containing ret- inal pigment; 7, one of the six Structure of an ium of Calliphora ENTOMOLOGY Each ommatidium is adapted to trans- mit light along its axis only (Fig. 143), as oblique rays are lost by ab- sorption in the black pigment which surrounds the crystalline cone and the axial rhabdom. Along the rhabdom, then, light can reach and affect the terminations of the optic nerve. Each ommatidium does not itself form a picture; it simply preserves the inten- sity and color of the light from one particular portion of the field of vision; and when this is done by hun- dreds or thousands of contiguous om- matidia, an image results. All that the painter does, who copies an object, is to put together patches of light in the same relations of quality and posi- tion that he finds in the object itself and this is essentially what the com- pound eye does, so far as can be in- ferred from its structure. Exner, removing the cones with the corneal cuticula (in Lampyris) , looked through them from behind with the aid of a microscope and found that the images made by the separate omma- tidia were either very close together or else overlapped one another, and that in the latter case the details corre- sponded; in other words, as many as twenty or thirty ommatidia may co- operate to form an image of the same portion of the field of vision; this retinal cells which compose the retinula; rh, rhab- dom, composed of six rhabdomeres; t¢, trachea; tv, tracheal vesicle.—After Hickson. ANATOMY AND PHYSIOLOGY 113 “superposition ” image being correspondingly bright—an ad- vantage, probably, in the case of nocturnal insects. Large convex eyes indicate a wide field of vision, while small numerous facets mean distinctness of vision, as Lubbock has pointed out. The closer the object the better the sight, for the greater will be the number of lenses employed to produce the impres- sion, as Mollock says. If Muiller’s theory is true, an image may be formed 8 aN | of an object at any reasonable distance, no power of accommodation being ne- cessary; while if, on the other hand, each cornea with its crystalline cones iG tA?) A C—— had to form an image after the manner of an ordinary hand-lens, only objects at a definite distance could be imaged. The limit of the perception of form by insects is placed at about two meters for Lampyris, 1.50 meters for Lepi- doptera, 68 cm. for Diptera and 58 cm. for Hymenoptera. Diagram of outer, trans- parent portion of an omma- It is generally agreed, however, that tidium to illustrate _ the the compound eyes are specially adapted hee Ueto to perceive movements of objects. The Sc Ca ee ton sensitiveness of insects to even slight length emerges at C. , iris movements is a matter of common ob- 7 servation ; often, however, these insects can be picked up with the fingers, if the operation is performed slowly until the insect is within the grasp. A moving object affects different facets in succession, without necessitating any turning of the eyes or the head, as in vertebrates. Furthermore, on the same principle, the compound eyes are serviceable for the perception of form when the insect itself is moving rapidly. The arrangement of the pigment depends adaptively upon the quality of the light, as Stefanowska and Exner have shown; thus, when the light is too strong, the iris and retinal 9 114 ENTOMOLOGY pigment cells elongate around the ommatidium and their pig- ment granules absorb from the cone cells and rhabdom the excess of light. If the light 1s weak, they shorten, and absorb but a minimum amount of light. Origin of Compound Eye.—The compound eye is often said to represent a group of ocelli, chiefly for the reason that externally there appears to be a transition from simple eyes, through agglomerate eyes, to the facetted type. This plausi- ble view, however, is probably incorrect, for these reasons among others. In the ocellus, a single lens serves for all the retinulz, while in the compound eye there are as many lenses as there are retinulz. Moreover, ocelli do not pass directly into compound eyes, but disappear, and the latter arise independently of the former. Probably, as Grenacher holds, both the ocellus and the com- pound eye are derived from a common and simpler type of eye—are “‘sisters,’ so to speak, derived from the same parentage. Perception of Light through the Integument.—In vari- ous insects, as also in earthworms, blind chilopods and some other animals, light affects the nervous system through the general integument. Thus eyeless dipterous larve avoid the light, or, more precisely, they retreat from the rays of shorter wave-length (as the blue), but come to rest in the rays of longer wave-length (red), as 1f they were in darkness (see page 350). The blind cave-beetles of the genus Anophthal- mus react to the light of a candle (Packard). Graber found that a cockroach deprived of its eyesight could still perceive light, but Lubbock found that an ant whose eyes had been covered with an opaque varnish became indifferent to light. Color Sense.—Insects undoubtedly distinguish certain col- ors, though their color sense differs in range from our own. Thus ants avoid violet light as they do sunlight, but probably cannot distinguish red or orange light from darkness; on the other hand, they are extremely sensitive to the ultra-violet rays, which make no sensible impression upon us. Honey ANATOMY AND PHYSIOLOGY I15 bees frequently select blue flowers; white butterflies (Pieris) prefer white flowers, and yellow butterflies (Colias) appear to alight on yellow flowers in preference to white ones ( Pack- ard). In fact, the color sense is largely relied upon by insects to find particular flowers and by butterflies to a large extent to find their mates. To be sure, insects will visit flowers after Fic. 144. Alimentary tract of a collembolan, Orchesella. F, fore gut; H, hind gut; M, mid gut; c, cardiac valve; cm, circular muscle; /m, longitudinal muscle; p, pharynx; py, pyloric valve. the brightly colored petals have been removed or concealed, as Plateau found, but this does not prove that the colors are of no assistance to the insect, though it does show that they are not the sole attraction—the odor also being an important guide. Problematical Sense Organs.—As all our ideas in regard to the sensations of insects are necessarily inferences from our own sensory experiences, they are inevitably inadequate. While it is certain that insects have at least the senses of touch, taste, smell, hearing and sight, it is also certain that these senses of theirs differ remarkably in range from our own, as we have shown. We can form no accurate conception of these ordinary senses in insects, to say nothing of others that insects have, some of which are probably peculiar to insects. Thus they have many curious integumentary organs which from their structure and nerve connections are probably sensory end-organs, though their functions are either doubtful or un- known. Such an organ is the sensillum placodeum (p. 95), the use of which is very doubtful, though the organ is pos- sibly affected by air pressure. Insects are extremely sensitive 116 ENTOMOLOGY to variations of wind, temperature, moisture and atmospheric pressure, and very likely have special end-organs for the per- ception of these variations; indeed, the sensilla trichodea are probably affected by the wind, as we have said. The halteres of Diptera, representing the hind wings, con- tain sensory organs of some sort.. They have been variously regarded as olfactory (Lee),auditory (Graber),and as organs of equilibration. When one or both halteres are removed, the fly can no longer maintain its equilibrium in the air, and Weinland holds that the direction of flight is affected by the movements of these “ balancers.”’ 6. DIGESTIVE SYSTEM The alimentary tract in its simplest form is to be seen in Thysanura, Collembola and most larve, in which (Fig. 144) it is a simple tube extending along the axis of the body and Alimentary tract of a grasshopper, Melanoplus differentialis. c, colon; cr, crop; gc, gc, gastric ceca; i, ileum; m, mid intestine, or stomach; mt, Malpighian, or kid- ney, tubes; 0, esophagus; p, pharynx; 7, rectum; s, salivary gland of left side. consisting of three regions, namely, fore, mid and hind gut. These regional distinctions are fundamental, as the embry- ology shows, for the middle region is entodermal in origin and the two others are ectodermal, as appears beyond. There are many departures from this primitive condition, and the most specialized insects exhibit the following modifi- cations (Figs. 145, 146) of the three primary regions: Fore intestine (stomodeum) : mouth, pharynx, cesophagus, crop, proventriculus (gizzard), cardiac valve. ANATOMY AND PHYSIOLOGY 7 Mid intestine (mesenteron) : ventriculus (stomach). Hind intestine (proctodeum) : pyloric valve, ileum, colon, rectum, anus. Stomodzum.—The mouth, the anterior opening of the food canal, is to be dis- tinguished from the pharynx, a dilatation for fecepiion; Of food... In the pharynx of mandib- ulate insects the food is acted upon by the saliva; in suctorial forms the pharynx acts as a pump- ing organ, in the manner already described. The wsophagus is com- monly a simple tube of small and uniform cali- ber, varying greatly in length according to the kind of insect. Passing between the commissures that connect the brain with the subcesophageal ganglion (Fig. 113), the cesophagus leads _ grad- ually or else abruptly into the crop or gizzard, or when these are absent, directly into the stomach. In addition to its fune- tion of conducting food, the cesophagus is some- Fic. 146. Digestive system of a beetle, Carabus. a, anal gland; c (of fore gut), crop; c (of hind gut), colon, merging into rectum; d, evacuating duct of anal gland; g, gastric ceca; 1, ileum; m, mid intestine; mt, Mal- pighian tubes; 0, cesophagus; p, proventricu- lus; 7, reservoir.—After KoLseE. times glandular, as in the grasshopper, in which it is said to secrete the ‘“‘ molasses ’’ which these insects emit. 118 ENTOMOLOGY The crop is conspicuous in most Orthoptera (Fig. 145) and Coleoptera (Fig. 146) as a simple dilatation. In Neuroptera (Fig. 147) its capacity is increased by Fic. 147. means of a lateral pocket—the food reser- voir; this in Lepidoptera, Hymenoptera and Diptera is a sac (Fig. 148, c) commu- nicating with the cesophagus by means of a short neck or a long tube, and serving as a temporary receptacle for food. In her- bivorous insects the crop contains glucose formed from starch by the action of saliva or the secretion of the crop itself; in car- nivorous insects this secretion converts albuminoids into assimilable peptone-like substances. Next comes the enlargement known as the proventriculus, or gizzard, which 1s present in many insects, especially Orthop- tera and Coleoptera (Fig. 146), and is usually found in such mandibulate insects as feed upon hard substances. The pro- of Ventriculus is lined with chitinous teeth or Digestive system Myrmeleon larva. ¢ ridges for straining, the foodssameaumae cecum; cr, crop; m, mid intestine; mt, Malpighian powerful circular muscles to squeeze the tubes; s, spinneret.— After MEINERT. food back into the stomach, as well as longitudinal muscles for relaxing, or open- ing, the gizzard. Some authors maintain that the proventricu- lus not only serves as a strainer, but also helps to commuinute the food, like the gizzard of a bird. : In most insects a cardiac valve guards the entrance to the stomach, preventing the return of food to the gullet. This valve (Figs. 144, 149) is an intrusion of the stomodzeum into. the mesenteron, forming a circular hp which permits food to pass backward, but closes upon pressure from behind. Mesenteron.—The ventriculus, otherwise known as the ANATOMY AND PHYSIOLOGY 119 mid imtestine, or stomach, is usually a simple tube of large caliber, as compared with the cesophagus or intestine, and into Fic. 148. S i mt Ce C \ : ie 9 7 RK Alimentary tract of a moth, Sphinx. c, food reservoir; cl, colon; cm, cecum; 1, ileum; m, mid intestine; mt, Malpighian tubes; 0, wsophagus; r, rectum; s, salivary gland.— After WAGNER. the ventriculus may open glandular blind tubes, or gastric ceca (Figs. 145, 146); these, though numerous in some insects, are commonly few in number and restricted to the ante- rior region of the stomach. ‘The gastric czca of Orthoptera secrete a weak acid which emulsifies fats, or one which passes forward into the crop, there to act upon albuminoid substances. In the stomach the food may be acted upon by a fluid secreted by specialized cells of the epithe- lial wall. In various insects, certain cells project periodically into the lumen of the stomach as papillee, which by a process of constriction become separated from the parent cells and mix bodily with the food. This phenomenon takes place in the larva ‘of Ptychoptera (van Gehuchten), also in nymphs of Odonata (Needham), and is probably of widespread occurrence among insects. The ‘chief function, #ofv the Fic. 149. Cardiac valve of young muscid larva. agus; p, proventriculus; v, valve. In an older larva the valve projects into the mid intestine.— After KowaLervsky. 0, césoph- 120 EN TOMOLOGY stomach, however, is absorption, which is effected by the general epithelium. Physiologically, the so-called stomach of an insect is quite unlike the stomach of a vertebrate, being more like an intestine. Proctodzum.—At the anterior end of the hind intestine there is usually a pyloric valve, which prevents the contents of the intestine from returning into the stomach. This valve may operate by means of a sphincter, or constricting, muscle, or may, as in Collembola (Fig. 144), con- sist of a backward-projecting circular ridge, or lip, which closes upon pressure from behind. In its primitive condition the hind intestine is a simple tube (Fig. 144).. Usually, however, it presents two or FIG. -150. even three specialized regions, namely and in order, tlewm, colon and rectum (Fig. 145). The hind intestine varies greatly in length and is frequently so long as to be thrown into convolutions (Fig. 150). The ileum is short and stout in grasshoppers (Fig. 145) ; long, slender and convoluted in many carniy- orous beetles; and quite short in cater- Digestive system of Belos- pillars and most other larve; its func- toma. c, cecum; 1, ileum; A 2 5 m, mid. intestine: mi, Mal. tion is absorption. ~The scolonpmorsa Pighian tubes; 7, salivary absent, is evident in Orthoptera and reservoir; s, salivary gland. —After Locy, from the Lepidoptera and may bear (Benacus, aceon eae Dytiscus, Silphidee, Lepidoptera) a con- spicuous czecal appendage (Figs. 148, 150) of doubtful func- tion, though possibly a reservoir for excretions. The colon contains indigestible matter and the waste products of diges- tion, including the excretions of the Malpighian tubes. The rectum (Fig. 145) is thick-walled, strongly muscular and often folded internally. Its office is to expel excrementitious matter, consisting largely of the indigestible substances chitin, cellulose ANATOMY AND PHYSIOLOGY I2T and chlorophyll. The rectum terminates in the anus, which opens through the last segment of the abdomen, always above the genital aperture. Histology.—The epithelial wall of the alimentary tract is a single layer of cells (Fig. 151), which secretes the imtima, or lining layer, and the basement membrane—a delicate, struc- tureless enveloping layer. The intima, which is contin- uous with the external cutic- ula, is chitinous in the fore and hind gut (which are ectodermal in origin), but pce not in the mid gut (entoder- ei mal), and usually exhibits BS extremely fine transverse ae alt striz, which are due prob- ie 3 7C ably to minute pore canals. Surrounding the basement membrane {Sea SERIES OF 'C17— Wall of mid intestine of silk worm, cular muscles and outside transverse section. b, basement membrane; c, circular muscle; 7, intima; /, longitudinal these is a laver ot longitudi- muscle; ”, , nuclei of epithelial cells; s, secretory cell. ses aw nal muscles. The circular muscles serve to constrict the pharynx in sucking insects and, in general, to squeeze backward the contents of the alimentary canal by successively reducing its caliber. The longitudinal muscles, restricted almost entirely to the mid intestine, act in opposition to the constricting muscles to en- large the lumen of the food canal and in addition to effect peristaltic movements of the stomach. The intima of the crop is sometimes shaped into teeth, and that of the proventriculus is heavily chitinized and variously modified to form spines, teeth or ridges. Salivary Glands.—In their simplest condition, the salivary glands are a pair of blind tubes (Fig. 152), one on each side of the cesophagus and opening separately at the base of the hypopharynx. Commonly, however, the glands open through 122 . ENTOMOLOGY two salivary ducts into a common, or evacuating, duct; a pair A simple salivary gland of Cdecilius. c, canal; d, duct; g, g, gland- ular cells—After KoLBE. of salivary reservoirs (Fig. 153) may be present, and the glands are frequently branched or lobed, and, though usually confined to the head, may extend into the thorax or even into the abdomen. Many insects have more than one pair of glands opening into the pharynx or cesophagus; thus the honey bee has six pairs and Hymenoptera as a whole have as many as ten different pairs. Though all these are loosely spoken of as salivary glands, it is better to restrict that term to the pair of glands that open at the hypo- pharynx. All these cephalic glands are evagina- tions of the stomodzum (ectodermal in origin) and consist of an epithelial layer with the customary intima and basement membrane (Mig. 154). “The aiuclemiame large, as is usually the case in glandular cells, and the cytoplasm consists of a dense framework (appearing in sections as a network) enclosing vacuoles of a clear substance—the secretion; the chitinous Right salivary gland of cockroach, ventral aspect. c, common duct; g, gland; h, hypopharynx; r, reservoir.—After MriaLtt and DENNY. ANATOMY AND PHYSIOLOGY 12 io) intima is penetrated by fine pore canals through which the secretion passes. In many insects, notably the cockroach, the common duct is held distended by spiral threads which give the duct much the appearance of a tra- chea. In herbivorous insects the saliva changes starch into glucose, as in vertebrates; in carnivorous forms it ” >- acts on proteids and is often used to poison the prey, as in the larva of Dytiscus. In the mosquito each gland is three-lobed (Fig. 155) ; the Histoloey. of ealieery: gland miuddielobe is-different in appearance ~°f Cectius, radial! section. , basement membrane; c, canal; from the two others and secretes g¢, glandular cell; i, intima; n, nucleus.—After KoLBE. Fic. 154. a poisonous fluid which is carried out along the hypopharynx. Though this poison is said to facili- tate the process of blood-sucking by preventing the coagulation of the blood, its primary use was perhaps to act upon proteids in the juices of plants. Malpighian Tubes.—The kidney, or Malpighian, tubes, present in nearly all insects, are long, slender, blind tubes open- ing into the intestine imme- diately behind the stomach as a ule (Ghigs 14549146), ss = but always into the intestine. One of the three-lobed salivary glands “The number of kidney tubes is of a mosquito. The middle lobe secretes : ee : A A the poison.—After Mactosxiz, from the VE€ITY different in different 11l- American Naturalist, Fic. 155. sects; Collembola have none, while Odonata have fifty or more and Acridiidze as many as one hundred and fifty; commonly, however, there are four or six, as in Coleoptera, Lepidoptera and many other orders. Not more than six and frequently only four occur in the em- bryo (Wheeler), though these few embryonic tubes may sub- sequently branch into many. 124 ENTOMOLOGY The Malpighian tubes (Fig. 156) are evaginations of the proctodeum and are consequently ectodermal. A cross sec- tion of a tube shows a ring of from one Fic. 156. to six or more large polygonal cells (Fig. 157), which often project into the lumen of the tube; the nuclei are usually large and may be branched, as in Lepidoptera. A chitinous intima, traversed by pore- canals, lines the tube, and a delicate base- ment membrane is present, surrounded by a peritoneal layer of connective tissue. Furthermore, the urinary tubes are richly supplied with trachez. In function, the Malpighian tubes are analogous to the vertebrate kidneys and contain a great variety of substances, chief among which are uric acid and its derivatives (such as urate of sodium and of ammo- nium), calcium oxalate and calcium car- Portion of Malpighian bonate. eee tee Parts of the fat-body may also be cecropia, surface view. : concerned in excretion; thus the fat- body in Collembola and Orthop- tera serves for the permanent stor- age of urates. 7. CIRCULATORY SYSTEM Insects, unlike vertebrates, have no system of closed blood-vessels, but the blood wanders freely through the body cavity to enter Gross section ve Malpipiieanenee eventually the dorsal vessel, which °% s!:vonn, Bomij= | A ; basement membrane; c, crystals; 1, resembles a heart merely in being intima; 1, lumen; n, nucleus; , a propulsatory organ peritoneal layer. Greatly magnified. c oc > S¢ . Dorsal Vessel.—The dorsal vessel (Figs. 158, 162) is a delicate tube extending along the median dorsal line immedi- ANATOMY AND PHYSIOLOGY 12 wn ately under the integument. A simple tube in some larve, it consists in most adults chiefly of a series of chambers, each of FIG. 159. Fic. 158. 2H Diagram of a portion of the heart of a dragon fly nymph, Epitheca. o, ostium; v, valve; the ar- rows indicate the course of the blood. — After Kose. Fic. 160. $< D l y | IN (i I M : hee Ni Dorsal vessel of beetle, Lucanus. a, aorta; al, alary muscle; o, ostium. — After Straus-DURCKHEIM. Diagrammatic cross section of pericardial region of a grasshopper, Céedipoda. a, alary muscle; d, dorsal vessel; s, suspensory mus- cles; sp, septum.—After GRABER. Blood corpuscles of a grasshopper, Stenobothrus. a-f, corpuscles covered with fat- globules; g, corpuscle after treatment with glycerine, showing nucleus.—After GraBErR. which has on each side a valvular opening, or ostium (Fig. 159), which permfts the ingress of blood but opposes its egress ; 126 ENTOMOLOGY within the chambers occur other valvular folds that allow the blood to move forward only. Wuth few exceptions (Ephe- meridz) the dorsal vessel is blind behind and the blood can enter 1t only through the lateral ostia. Aorta.—The posterior, or Bae 02 pulsating portion (heart) of the dorsal vessel is confined \ ee for the most part to the abdo- men; the anterior portion, or i“ gorta, extends as a/"simple = | | x attenuated tube through the thorax and into the head, se eae — where it passes under the brain and usually divides into | | two branches (Fig. 162); each of which may again branch. » In> (they theadsateme | | | blood leaves the aorta ab- ruptly and enters the general body cavity. Ny Alary Muscles.—Extend- V ing outward from the “heart,” Diagram to indicate the course of the or propulsatory porion, ame blood in the nymph of a dragon fly, : S Epitheca. a, aorta; h, heart; the arrows making with the dorsal wall Bee eu eer aes by currents of of the body a pemearaual chamber, isa loose diaphragm, formed largely by paired fan-like muscles—the alary muscles (Figs. 158, 160). These are thought to assist the heart in its propulsatory action. Structure of the Heart.—The dorsal vessel has a delicate lining-membrane, or intima, and a thin enveloping membrane; between these, in the heart, is a layer of fine muscle fibers, cir- cular or spiral in direction, which effect the contractions of the organ. Ventral Sinus.—In many if not most insects a pulsatory septum (Fig. 177, v) extends across the floor of the body cav- ANATOMY AND PHYSIOLOGY Le7i ity to forma sinus, in which the blood flows backward, bathing the ventral nerve cord as it goes. This ventral sinus supple- ments the heart in a minor way, as do also the local pulsatory sacs which have been discovered in the legs of aquatic Hemip- tera and the head of Orthoptera. Blood.—The blood, or hemolymph, of an insect consists chiefly of a watery fluid, or plasma, which contains corpuscles, or leucocytes. Though usually colorless, the plasma is some- times yellow (Coccinellidz, Meloidze), often greenish in her- bivorous insects from the presence of chlorophyll, and some- times of other colors; often the blood owes its hue to yellow or red drops of fat on the surface of the blood corpuscles (Hig. 161). Leucocytes.—The corpuscles, or leucocytes, are minute nucleated cells, 6 to 30 » in diameter, variable in form even in the same species but commonly (Fig. 161) round, oval or ovate in profile, though often disk-shaped, elongate or amce- boid in form. Function of the Blood.—The blood of insects contains many substances, including egg albumin, globulin, fibrin, iron, potassium and sodium (Mayer), and especially such a large amount of fatty material that its principal function is probably one of nutrition; the blood of an insect contains no red cor- puscles and has little or nothing to do with the aeration of tissues, that function being relegated to the tracheal system. Circulation.—The course of the circulation is evident in transparent aquatic nymphs or larve. In odonate or ephe- merid nymphs, currents of blood may be seen (Fig. 162) tlow- ing through the spaces between muscles, trachez, nerves, etc., and bathing all the tissues; separate outgoing and incoming streams may be distinguished in the antennz and legs; the returning blood flows along the sides of the body and through the ventral sinus and the pericardial chamber, eventually to enter the lateral ostia of the dorsal vessel. A circulation of blood occurs in the wings of freshly emerged Odonata, Ephe- 128 ENTOMOLOGY merida, Coleoptera, Lepidoptera, etc., the currents trending along the trachez; this circulation ceases, however, with the drying of the wings. The chambers of the dorsal vessel expand and contract suc- © cessively from behind forward. At the expansion (diastole) of a chamber its ostia open and admit blood; at contraction (systole) the ostia close, as well as the valve of the chamber next behind, while the chamber next in front expands, afford- ing the only exit for the blood. The valves close partly through blood-pressure and partly by muscular action. The rate of pulsation depends to a great extent upon the activity of the insect and upon the temperature and the amount of oxygen or carbonic acid gas in the surrounding atmosphere. Oxygen accelerates the action of the heart and carbonic acid gas retards it. A decrease of 8° or 10° Ch im the casera caame silkworm lowers the number of beats from 30 or 40 to 6 or 8 per minute. The more active an insect, the faster its heart beats. . The rate of pulsation is very different in the different stages of the same insect. Thus in Sphinx ligustri, according to Newport, the mean number of pulsations in a moderately active larva before the first moult is about 82 or 83 per minute; before the second moult, 89, sinking to 63 before the third moult, to 45 before the fourth, and to 39 in the final larval stage; the force of the circulation, however, increases as the pulsations decrease in number. During the quiescent period immediately preceding each moult, the number of beats is about 30. In the pupal stage the number sinks to 22, and then lowers until, during winter, the pulsations almost cease. The moth in repose shows 41 to 50 per minute, and after flight as many as 139. 8. Fat-Bopy The fat-body appears (Fig. 163) as many-lobed masses of tissue filling in spaces between other organs and occupying a large part of the body cavity. The distribution of the fat- body is to a certain extent definite, however, for the fat-tissue ANATOMY AND PHYSIOLOGY 129 conforms to the general segmentation and is arranged in each segment with an approach to symmetry. Much of this tissue forms a distinct peripheral layer in each segment, and masses of fat-body occur constantly on each side of the alimentary FTG 163! TT Wins ET BS TM peru ea @ Transverse section of the abdomen of a caterpillar, Pieris rape. b, blood corpus- cles; c, cuticula; d, dorsal vessel; f, fat-body; g, ganglion; h, hypodermis; /, leg; m, muscle; mi, mid intestine, containing fragments of cabbage leaves; mt, Malpighian tube; s, silk gland; sp, spiracle; tr, trachea. tract and also at the sides of the dorsal vessel, in the latter case forming the pericardial fat-body. Fat-Cells.—The fat-cells (Fig. 164) are large and at first more or less spherical, with a single nucleus (though there are said to be two in Apis and several in Musca), but the cellular Ke) 130 ENTOMOLOGY structure of the fat-tissue is often difficult to make out because the cells are usually filled with globules of fat (Fig. TORE Be Bk while old cells break down, leaving only a disorderly net- work. The fat-cells sometimes contain an albuminoid — sub- stance, and usually the fat-body B includes considerable quantities Fat-cells of a caterpillar, Pieris. A, ot uric acid or its derivatives, cells filled with drops of fat; B, cell freed of fat-drops, showing nucleus— frequently in the form of con- After Kose. : : spicuous concretions. Functions.—The physiology of the fat-system is still ob- scure. Probably the fat-body combines several functions. In caterpillars and other larve it furnishes a reserve supply of nutriment, at the expense of which the metamorphosis takes place; the amount of fat increases as the larva grows, and diminishes in the pupal stage, though some of it lasts over to furnish nourishment for the imago and its germ cells. The gradual accumulation of uric acid and urates in the fat- Fic. 165. body indicates an excretory function, particularly in Col- lembola, which have no Mal- pighian tubes. ‘The intimate association between the ulti- mate tracheal branches and the fat-body has led some authorities to ascribe a res- piratory function to the lat- ter, =f) close: ‘felatiom on some sort exists also be- tween the fat-system and Section through fat-body Gerateeaene the blood-system; fat-cells are found free in the blood, and the blood corpuscles originate in the thorax and abdo- showing nucleated cells, loaded with drops of fat. men from tissues that can scarcely be distinguished from ANATOMY AND PHYSIOLOGY 131 fat-tissues. The corpuscles (leucocytes, or phagocytes) which in some insects absorb effete larval tissues during meta- morphosis have been by some authors regarded as wandering fat-cells. Cells constituting the pericardial fat-body are at- tached to the lateral muscles (alary muscles) of the dorsal vessel, but almost nothing is known as to their function. Associated with the fat-body proper are the peculiar cells known as anocytes. These occur in most insects, in segmentally-arranged clusters on each side of the abdomen, and consist of exceptionally large cells, Fic. 166. more or less round or oval (Fig. 166), each with a large round, oval or elon- gate nucleus. These peculiar cells are usually separate from one another, but Enocytes and accom- are held in clusters by tracheal branches. P2™yimg trachee, from ~ abdomen of a silkworm. Their function is unknown. Finally, the fat-body is the basis of the luminosity, or so-called phospho- rescence, of insects. Luminosity.—This phenomenon appears sporadically and by various means in protozoans, worms, insects, fishes and other animals. Luminosity in insects, though sometimes merely an incidental and pathological effect of bacteria, 1s usu- ally produced by special organs in which light is generated probably by the oxidation of a fatty substance. There are not many luminous insects. Those best known are the Mexican and West Indian beetles of the genus Py- rophorus (Elateridz), in which the pronotum bears a pair of luminous spots, and the common fire-flies (Lampyride). In Lampyridze, the light is emitted from the ventral side of the posterior abdominal segments. In our common Photius, the seat of the light is a modified portion of the fat-body—a photogenic plate, situated immediately under the integument and supplied with a profusion of fine tracheal branches. The cells of the photogenic plate, it is said, secrete a substance which iS) T3 EN TOMOLOGY undergoes rapid combustion in the rich supply of oxygen fur- nished by the trachez. * The rays emitted by the common fire-flies are rethatkete in being almost entirely light rays, with almost no thermal or Fic. 167. Tracheal system of an insect. a, an- tenna; b, brain; /, leg; mn, nerve cord; p, palpus; s, spiracle; st, spiracular, or stigmatal, branch; ¢, main tracheal trunk; v, ventral branch; ws, visceral branch.— After Kose. actinic’ rays. Accordimpaies Young and Langley, the radia- tions of an ordinary gas-flame contain less than three per cent. of visible rays, the remainder being heat or chemical rays, of no value for illuminating pur- poses; while the light-giving efficiency of the electric are is only ten per cent. and that of sunlight only thirty-five per cent. The light of the fire- fly, however, may be rated at one hundred per cent.; this light, then, is perfect, and as yet unapproached by artificial means. As to the use of this lumi- nosity, there is a ‘Semegal opinion that the lght exists for the purpose of sexual attraction—a_ belief held by the author in regard to Pho- tinus, at least. Another view is that the light is a warning signal to nocturnal birds, bats or other insectivorous animals; this is supported by the fact that lampyrids are refused by birds in general, after ex- perience; young birds readily snap at a fire-fly for the first time, but at once reject it and thereafter pay no attention to these insects. ANATOMY AND PHYSIOLOGY I ios) ios) 9g. RESPIRATORY SYSTEM In insects, as contrasted with vertebrates, the air itself is conveyed to the remotest tissues by means of an elaborate sys- tem of branching air-tubes, or trachee, which receive air through paired segmentally-arranged spiracles. Each spiracle is commonly the mouth of a short tube which opens into a main tracheal trunk (Fig. 167) extending along the side of Diagrammatic cross section of the thorax of an imsect. a, alimentary canal; d, dorsal vessel; g, ganglion; s, spiracle; w, wing; 7, dorsal tracheal branch; 2, visceral branch; 3, ventral branch. the body. From the two main trunks branches are sent which divide and subdivide until they become extremely delicate tubes, which penetrate even between muscle fibers, between the ommatidia of the compound eyes and possibly enter cells. In most cases each main longitudinal trunk gives off in each seg- ment (Fig. 168) three large branches: (1) an upper, or dor- sal, branch, which goes to the dorsal muscles; (2) a middle, or visceral, branch, which supplies the alimentary tract and the reproductive organs; (3) a lower, or ventral, branch, which pertains to the ventral ganglia and muscles. In many swiftly-flying insects (dragon flies, beetles, moths, flies and bees) there occur tracheal pockets, or air-sacs, which 134 ENTOMOLOGY were formerly and erroneously supposed to diminish the weight of the insect, but are now regarded as simply air- reservoirs. Types of Tracheation.—Two types of tracheal system are distinguished for convenience: (1) The primary, open, or holopneustic type . described above, in which the spiracles are functional; (2) the sec- ondary, closed, or apneustic type, in which the spiracles are either functionless or ab- sent. This type is illustrated in Collembola and such aquatic Fic. ‘160. jf y Gj nymphs and larve as breathe . WwW) either directly through the skin IX MY) or else by means "or @eate: NU The two types, however, are = connected by all sorts of inter- Lateral gill from abdomen of a May ‘Mediate stages. fly nymph, Hexagenia variabilis. En- Tracheal Gills—In many larged. aquatic nymphs and larvee the spiracles are suppressed (though they become functional in the imago) and respiration is effected by means of gills; these are cuticular outgrowths which usually, ° though not invariably, contain trache:e, and are commonly lateral or caudal in position. Lateral tracheal gills are highly developed in ephemerid nymphs (Fig. 169), in which a pair occurs on Caudal gills of an ‘i c har ee pa Ae ‘s agrionid nymph, en- some or all of the first seven segments |.) oag of the abdomen; a few genera, how- ever, have cephalic or thoracic gills. Larvae of Trichoptera have paired abdominal gills varying greatly in form and posi- tion, and Perlidze often have paired thoracic gills. Caudal tracheal gills are conspicuous in nymphs of Agrionide (Fig. 170) as three foliaceous appendages. A few coleopterous ANATOMY AND PHYSIOLOGY 135 larvee of aquatic habit, as Gyrinus and Cnemidotus, possess tracheal gills, as do also caterpillars of the genus Paraponyx (Fig. 171), which feed on the leaves of several kinds of water plants. Though manifold in form, tracheal gills are generally more or less foliaceous or filamentous, presenting always an ex- tensive respiratory surface; their integu- ment is thin and the trachez spread closely beneath it. These adaptations are often supplemented by waving move- ments of the gills, as in May fly nymphs, and by frequent movements of the insect from one place to another. Especially noteworthy are the rectal tracheal gills of odonate nymphs. In these insects the lining of the rectum forms numerous papillz or lamella, which Caterpillar of Para- ponyx obscuralis, to show tracheal gills. Length, 15 mm.—After Hart. ieee 72) Larva morpha of Bittaco- clavipes, show- ing respiratory tube. Natural Hart. size. — After contain a profusion of delicate tracheal branches; these are bathed by water drawn into the rectum and then expelled, at rather irregular intervals. A similar rectal respiration occurs also in ephemerid nymphs and mosquito larve. A few forms, chiefly Perlide, are exceptional in retaining tracheal gills in the adult stage; in some imagines they are merely vestiges of the nymphal gills, but in others, such as Pteronarcys (Fig. 18), which habitually dips into the water and rests in moist situations, the gills probably supplement the spira- cles. Further details on the respiration of aquatic insects are given in Chapter tN . 130 ENTOMOLOGY Spiracles.—The paired external openings of the trachez occur on the sides of the thorax and abdomen, there being never more than one pair to a segment. Though the thysa- nuran Japys has I1 pairs, no winged insect has more than 10; although there are in all 12 segments which may bear spiracles —the three thoracic and the first nine abdominal segments. ( Additional details are given on page 60. ) The spiracles, or stigmata, are usually provided with bris- tles, hairs or other processes to exclude dust; or the hairs of the body may serve the same purpose, as in Lepidoptera and Diptera; in many beetles the spiracles are protected by the elytra; in other beetles, however, and in many Hemiptera and Diptera the spiracles are unprotected externally. Larvee that live in water or mud may have spiracles at the end of a long Apparatus for closing the spiracular trachea in a beetle, Lucanus. A, trachea opened; B, closed; b, bow; bd, .band; c, external cuticula; 7, lever; m, muscle; s, spiracle; ¢, trachea.—After JupErcH and NITSCHE. tube, which can be thrust up into the pure air; this is true of the dipterous larve of Eristalis, Bittacomorpha (Fig. 172) and Culex (Fig. 229). Closure of Spiracles.— NG m aOG SQ Gobo Ua” a Transverse section of germ layers Transverse section of germ layers and and amnion folds of Clytra. a, am- embryonal membranes of Clytra. a, am- nion; e, ectoderm; i, inner layer nion; ac, amnion cavity; e, ectoderm; 1, (meso-entoderm): s, serosa.—Original, inner layer (meso-entoderm); s, serosa. based on Lécaillon’s figures. —After LECAILLON. layer, which is destined to form two layers, known respectively as entoderm and mesoderm. This formation of two primary germ layers by invagination or otherwise is termed gastrula- tion; it is an important stage in the development of all eggs, and among insects several variations of the process occur. Amnion and Serosa.—Meanwhile, the blastoderm has been DEVELOPMENT 149 folding over the germ band from either side, as shown in Fig. 190, and at length the two folds meet and unite to form two membranes (Fig. 191), namely, an inner one, or ammion, and an outer one, or serosa. I (chun Koy Germ band of a beetle, Melasoma, in three successive stages. A, unsegmented; B, with oral segments demarkated; C, with three oral, three thoracic and two ab- dominal segments.—After GRABER. Segmentation and Appendages.—On the germ band, which represents the ventral part of the future insect, the body segments are marked off by transverse grooves (Figs. 192, 194) ; this segmentation beginning usually at the an- terior end of the germ band and progressing backward. Furthermore, an anterior in- ‘ = 5 iagra ati agitte secti folding oecurs ( Fig. T 93 ) ’ Diagrammatic sagittal section of hymenopterous egg to show stomodzal forming the stomodewm, (s) and proctodeal (p) invaginations = ; of the germ band (g).—After GRABER. from which the mouth, pharynx, cesophagus and other parts of the fore gut are to arise; a similar, but posterior invagination, or proctodeum 150 ENTOMOLOGY (Fig. 193), is the beginning, or fundament, of the hind gut. At the anterior end of the germ band is a pair of large procephalic lobes (Figs. 192, 194), which eventually bear the lateral eyes, and immediately behind these are the fundaments of the antenne. O. £ y---- mx poe Geer Dope — Hl + io a Cie a4 pe 7 F¢------a5 Te ee eo pr Ventral aspect of germ band of a Anurida antenna; a!-a®, abdominal appendages; i, intercalary appendage; /, left labial m, mandible; mx, illa; p, procephalic lobe; pr, proctodeum; f-#%, thoracic legs, collembolan, maritima. a, labrum; Ji, appendage; max- The fundaments of the primary paired ap- pendages are out-pocketings of the ecto- dermal germ band, and at first antennze, mouth parts and legs are all alike, except in their relative positions. Behind the antenne (in Thysanura and Collembola at least) appears a pair of rudimentary appendages (Fig. 194, 4) which are thought to represent the second antennz of Crustacea; instead of developing, they disappear in the embryo or else persist in the adult as mere rudiments. In front of these transitory itercalary appendages 1s the mouth-opening, above the labrum and clypeus are already indicated by a single, median evagination. Behind the mouth the mandibles, maxillz and labium are represented by three pairs of which fundaments, and in Thysanura and Col- lembola a fourth pair is present to form the superlingue (Fig. 195, sl), already re- ferred to. Next in order are ie?taiee pairs of thoracic legs (Fig. 194) and then, in many cases, paired abdominal appen- dages (Figs. 194, 196), indicating an ancestral myriopod-like condition; some of these abdominal limbs disappear in the embryo but others develop into abdomi- nal prolegs (Lepidoptera and Tenthredinidz ), external genital organs (Orthoptera, Hymenoptera, etc.) or other structures. The study of these embryonic fundaments sheds much light upon the morphology of the appendages and the subject of segmentation. DEVELOPMENT Sal Two Types of Germ Bands.—The germ band described above belongs to the simple overgrown type, exemplified in Clytra, in which the germ band retains its original posi- tion and the amnion and serosa arise by a process of over- growth (Figs. 190, 191), as distinguished from the mvaginated type, illustrated in Odonata, in which the germ band inva- ginates into the egg, as in Fig. 197, until the ventral surface Anterior aspect of embryonal mouth parts of a collembolan, Anurida maritima. a, antenna; /, labrum; /g, prothoracic leg; li, left fundament of labium; /n, lingua; m, mandible; mx, maxilla; », maxillary palpus; s/, superlingua.—After ForLsom. of the embryo becomes turned around and faces the dorsal side of the egg. In this event, a subsequent process of revolution occurs, by means of which the ventral surface of the embryo resumes its original position (Fig. 198). Dorsal Closure.—As was said, the germ band forms the ventral part of the insect. To complete the general form of the body the margins of the germ band extend outward and upward (Fig. 199) until they finally close over to form the dorsal wall of the insect. Besides this simple method, how- ever, there are several other ways in which the dorsal closure may be effected. Nervous System.—Soon after gastrulation, the ventral ner- vous system arises as a pair of parallel cords from cells (Fig. 152 ENTOMOLOGY 200, 2.) which have been derived by direct proliferation from those of the germ band, and are therefore ectodermal in origin. This primitive double nerve cord becomes constricted at inter- vals into segments, or meuromeres, which correspond to the segments of the germ band. Each neuromere consists of a Pie etce pair of primitive ganglia, and these ; oP are connected together by paired 1 1 ‘ nerve cords, which later may or may not unite into single cords; moreover, some of the ganglia finally unite to form compound ganglia, such as the brain and the subcesophageal ganglion. In front of the cesophagus (Fig. 55) are three neuromeres: (1) protocere- brum, which is to bear the com- pound eyes; (2) deutocerebrum, or antennal neuromere; (3) tritocere- brum, which belongs to the seg- ment which bears the rudimentary intercalary appendages spoken of above. Behind the cesophagus are, at most, four neuromeres, namely and in order, mandibular, super- lingual (found only in Collembola \e as yet), maxillary and labial. Seas ilae Ces ae Then follow the three thoracic gan- dominal appendages; e, end of glia and ten (usually) abdominal abdomen; /7, labrum; Ui, left 3 fundament of labium; i, labia’ - Ganglia. The first) three memes palpus; 7M, thoracic legs; ™ meres .always unite ftOgetiemumae mandible; mp, maxillary palpus; mx, maxilla; p, procephalic lobe; form the brain, and the next four pr, proctodeum.—After Ayers. - : (always three; but four in Col- lembola and perhaps other insects), to form the subceso- phageal ganglion. Compound ganglia are frequently formed also in the thorax and abdomen by the union of primitive ganglia. DEVELOPMENT Ws: Trachez.—The tracheze begin as paired invaginations of the ectoderm (Fig. 201, t) ; these simple pockets elongate and FIG: 107: Diagrammatic sagittal sections to illustrate invagination of germ band in Calop- teryx. a, anterior pole; ac, amnion cavity; am, amnion; b, blastoderm; d, dorsal; g, germ band; h, head end of germ band; , posterior pole; s, serosa; v, ventral; y, yolk.—After DBranpr. Fic. 1098. Diagrammatic sagittal sections to illustrate revolution of Calopteryx embryo. a, antenna; am, amnion; /, labium; /'-/, thoracic legs; m, mandible; mx, maxilla; s, serosa.—After BRANDT. 154 ENTOMOLOGY unite to form the main lateral trunks, from which arise the countless branches of the tracheal system. Mesoderm.—From the inner layer which was derived from the germ band by gastrulation (Figs. 189-191) are formed the important germ layers known as mesoderm and en- Fic. 199. Diagrammatic transverse sections to illustrate formation of dorsal wall in a beetle, Leptinotarsa. a, amnion (breaking up in C); g, germ band; s, serosa.—After WHEELER, from the Journal of Morphology. toderm. Most of the layer becomes mesoderm, and this splits on either side into chambers, or cwlom sacs (Fig. 200, c),a pair to each segment. In Orthoptera these ccelom sacs are large and extend into the embryonic appendages, but in Coleoptera, Lepidoptera and Hymenoptera they are small. These sacs Tansverse section of germ layers of Clytra. c, ceelom sac; n, neuroblasts (primitive nervous cells).—After LECAILLON. may share in the formation of the definite body-cavity, though the last arises independently, from spaces that form between the yolk and the mesodermal tissues. From the ccelom sacs develop the muscles, fat-body, dorsal vessel, blood corpuscles, ovaries and testes; the external sexual organs, however, as well as the vagina and ejaculatory duct, are ectodermal in origin. DEVELOPMENT 155 Entoderm.—At its anterior and posterior ends, the inner fayer just referred to gives rise to a mass of cells which are Fic. 201. Transverse section of abdomen of Clytra embryo at an advanced stage of develop- ment. a, appendage; e, epithelium of mid intestine; g, ganglion; m, Malpighian tube; mi, muscular layer of mid intestine; ms, muscle elements; my, mesenchyme (source of fat-body); s, sexual organ; ¢t, tracheal invagination.—After LECAILLON. destined to form the mesenteron, from which the mid intestine develops. One mass is adjacent to the blind end of the stomo- deal invagination and the other to that of the proctodzal in-folding. The two masses become U-shaped (Fig. 202), and the lateral arms of the two elongate and join so that the entodermal masses become connected by two lateral strands of cells; by overgrowth and undergrowth from these lateral strands a tube is formed which is destined to become the stomach, and by the disappearance of the partitions that separate the mesenteron from the stomodzum at one end and from the proc- todeum at the other end, the continuity Gimme salimentary. canal is* established. -)“8tamt0t tormaton of entoderm in Leptino- The fore and the hind gut, then, are ‘tarsa. e, e, entodermal EIG202) masses; mm, mesoderm. ectodermal. in ofigin, and the mid gut After Wuedzer. entodermal. 156 ENTOMOLOGY 2. EXTERNAL METAMORPHOSIS Metamorphosis.—One of the most striking phenomena of insect life is expressed by the term metamorphosis, which -means conspicuous change of form after birth. The egg of a butterfly produces a larva; this eats and grows and at length becomes a pupa; which, in turn, develops into an imago. These stages are so different (Fig. 27) that without experi- RiGEZ08) A Cyllene pictus. A, larva; B, pupa; C, imago. x 3. ence one could not know that they pertained to the same individual. Holometabola.—The more specialized insects, namely, Neuroptera, Mecoptera, Trichoptera, Lepidoptera, Coleoptera (Fig. 203), Diptera (Figs. 204, 29), Siphonaptera (Fig. 30) and Hymenoptera (Fig. 280), undergo this indirect, or com- plete,! metamorphosis, involving profound changes of form and distinguished by an inactive pupal stage. These insects are grouped together as Holometabola. Larvee receive such popular names as ‘ ‘caterpillar’ (Lepi- *These terms, though somewhat misleading in implication, are cur- rently used. ; DEVELOPMENT 157 doptera), “ grub” (Coleoptera), and “ maggot” (Diptera), while the pupa of a moth or butterfly (especially the latter ) ispcalied a ~ chrysalis.’’ Heterometabola.—In a grasshopper, as contrasted with a butterfly, the imago, or adult, is essentially like the young at birth, except in having wings and mature reproductive organs, and the insect is active throughout life; hence the metamor- phosis is termed direct, or incomplete. This type of trans- Fic. 204. Phormia regina. A, larva; B, puparium; C, imago. x 5. formation, without a true pupal period, is characteristic of the more generalized of the metamorphic insects, namely, Orthoptera, Platyptera, Plecoptera, Ephemerida (Fig. 19), Odonata (Fig. 20), Thysanoptera and Hemiptera (Fig. 205). These orders constitute the group Heterometabola. Within the limits of the group, however, various degrees of meta- morphosis occur; thus Plecoptera, Ephemerida and Odonata undergo considerable change of form; a resting, or quiescent, period may precede the imaginal stage, as in Cicada (Fig. 158 ENTOMOLOGY 206) ; while male Coccidz have what is essentially a complete metamorphosis. In fact, the various kinds of metamorphosis Cicada tibicen. A, imago emerging from nymphal skin; B, the cast skin; C, imago. Natural size. grade into one another in such a way as to make their classifi- cation to some extent arbitrary and inadequate. DEVELOPMENT 159 As there is no distinction between larva and pupa in most heterometabolous insects, it is customary to use the term nymph during the interval between egg and imago. Ametabola.—The most generalized insects, Thysanura and Collembola, develop to sexual maturity without a metamor- phosis; the form at hatching is retained essentially throughout life, there are no traces of wings even in the embryo, and there is no change of habit. These two orders form the group ‘Ametabola. All other insects have a metamorphosis in the broad sense of the term, and are therefore spoken of as Metab- ola. In this we follow Packard, rather than Brauer, who uses a somewhat different set of terms to express the same ideas. Stadium and Instar.—During the growth of every insect, the skin is shed periodically, and with each moult, or ecdysis, the appearance of the insect changes more or less. ‘The inter- vals between the moults are termed stages, or stadia. .To designate the insect at any particular stage, the term instar has been proposed and is growing in favor; thus the insect at hatching is the first instar, after the first moult the second imstar, and so on. Egg.—The eggs of insects are exceedingly diverse in form. Commonly they are more or less spherical, oval, or elongate, but there are innumerable special forms, some of which are Fic. 207. D Eggs of various insects. 4A, Musca domestica; C, chalcid, Bruchophagus funebris; D, butterfly, Papilio troilus; E, midge, Cecidomyia trifolii; F, hemipteron, Triphleps insidiosus; G, hemipteron, Podisus spinosus; H, fly, Drosophila ampelophila. Greatly magnified. butterfly, Polygonia interrogationis; B, house fly, > 160 ENTOMOLOGY quite fantastic. in! Pies 2074, JAS “resardsy sizessme Fic. 208. fi, } (etn Th (Wns Nth (I CTC CUT? ATT HUCCUUCCEAA ACCC cucu NTI WOETTTT UH Three eggs of the cabbage butterfly, Pieris rape. Greatly magnified, but all drawn to same scale. Something of the variety of form is shown st insect eggs can be distinguished by the naked eye; many of them tax the vision, however, for example, the elliptical eggs of Cecidomyia legumini- cola, which are but 300 mm. in length and .075, iimeamean width; the oval eggs of the cecropia moth, on the other hand, are as long as 3 mm. The egg-shell, or chorion, secreted around the ovum by cells of the ovarian follicle, may be smooth but is usually sculptured, frequently with ridges which, as in. lepidopterous eggs, may serve.to Sirensilien the shell. ~ (fhe ornamentation of the egg-shell is often exquisitely beautiful, though the par- ticular patterns displayed are probably of no use, being incidentally produced as impressions from the cells which Variations of form, size and pattern are frequent in secrete the chorion. eges of the same species, as appears in Rigs 208. Always the chorion is penetrated by one or more openings, constituting the micropyle, for the entrance of sperma- tozoa. Fic. 209. Chrysopa, laying eggs. Slightly enlarged. As a rule, the eggs when laid are accompanied by a fluid of some sort, which is secreted usually glands, opening into the vagina. by a cement. gland or This fluid commonly serves i) DEVELOPMENT IOI to fasten the eggs to appropriate objects, such as food plants, the skin of other insects, the hairs of mammals, etc.; 1t may form a pedicel, or stalk, for the egg, as in Chrysopa (Fig. 209); may surround the eggs as a gelatinous envelope, as in caddis flies, dragon flies, etc.; or may form a capsule enclosing the eggs, as in the cockroach. The number of eggs laid by one female differs greatly in different species and varies considerably in different individ- uals of the same species. Some of the fossorial wasps and bees lay only a dozen or so and some grasshoppers two or three dozen, while a queen honey bee may lay a million. Two females of the beetle Prionus laticollis had, respectively, 332 and 597 eggs in the abdomen (Mann). A. A. Girault gives the following numbers of eggs per female, from an examina- tion of twenty egg-masses of each species: Maximum. Minimum. Average. Thyridopteryx ephemereformis 1076 753 O4I Chsiocampa americana 466 313 375.5 Chionaspis furfura 84 33 66.5 Hatching.— Many larve, caterpillars for example, simply eat their way out of the egg-shell. Some maggots rupture the shell by contortions of the body. Some larve have spe- cial organs for opening the shell; thus the grub of the Colo- rado potato beetle has three pairs of hatching spines on its body (Wheeler) and the larval flea has on its head a tempo- rary knife-like egg-opener (Packard). The process of hatch- ing varies greatly according to the species, but has received very little attention. Larva.—Although larvee, generally speaking, differ from one another much less than their imagines do, they are easily referable to their orders and usually present specific differ- ences. Larve that display individual adaptive characters of a positive kind (Lepidoptera, for example) are easy to place, but larve with negative adaptive characters (many Diptera and Hymenoptera) are often hard to identify. 12s 162 * ENTOMOLOGY Thysanuriform Larve.—Two types of larve are recog- nized by Brauer, Packard and other authorities: thysanuri- form and eruciform; respectively generalized and specialized in their organization. The former term is applied to many larvee and nymphs (Fig. 210, C, D) on account of their resem- blance to Thysanura, of which Campodea and Lepisma are Fic. 210. ylypes of larve. A, B, Thysanura; C, D, thysanuriform nymphs; E-J, eruciform larve. A, Campodea; B, Lepisma; C, perlid nymph (Plecoptera); D, Libellula (Odonata); E, Tenthredopsis (Hymenoptera): F, Lachnosterna (Coleoptera); G, Melanotus (Coleoptera); H, Bombus (Hymenoptera); J, Hypoderma (Diptera). types. The resemblance lies chiefly in the flattened form, hard plates, long legs and antennz, caudal cerci, well-developed man- dibulate mouth parts, and active habits, with the accompanying sensory specializations. These characteristics are permanent in Thysanura, but only temporary in metamorphic insects, and their occurrence in the latter forms may properly be taken to indicate that these insects have been derived from ancestors which were much like Thysanura. Thysanuriform characters are most pronounced in nymphs of Blattidee, Forficulidee, Perlidze, Ephemeridz and Odonata, but occur also in the larvee of some Neuroptera (Mantispa) and Coleoptera (Carabide and Meloide). These primitive characters are gradually overpowered, in the course of larval evolution, by secondary, or adaptive, features. DEVELOPMENT 163 Eruciform Larve.—The prevalent type of larva among holometabolous insects is the eruciform (Fig. 210, E-/), illus- trated by a caterpillar or a maggot. Here the body is cylin- drical and often fleshy; the integument weak; the legs, anten- nee, cerci, and mouth parts reduced, often to disappearance ; the habits sedentary and the sense organs correspondingly re- duced. These characteristics are interpreted as being results of partial or entire disuse, the amount of reduction being propor- tional to the degree of inactivity. Extreme reduction is seen in the maggots of parasitic and such other Diptera as, secur- ing their food with almost no exertion, are simple in form, thin-skinned, legless, with only a mere vestige of a head and with sensory powers of but the simplest kind. Transitional Forms.—The eruciform is clearly derived from the thysanuriform type, as Brauer and Packard have shown, the continuity between the two types being established by means of a complete series of intermediate stages. The MIT S34 SW LBZ, \ . i roa Te. cS Mantispa. A, larva at hatching—thysanuriform; B, same larva just before first moult—now becoming eruciform. C, imago, the wings omitted; D, winged imago, slightly enlarged.—A and B after Braver; C and D after Emerton, from Packard’s Text-Book of Entomology, by permission of the Macmillan Co. beginning of the eruciform type is found in Neuroptera; where the campodeoid sialid larva assumes a quiescent pupal condi- tion. The key to the origin of the complete metamorphosis, 164 ENTOMOLOGY involving the eruciform condition, Packard finds in the neu- ropterous genus Mantispa (Fig. 211), the first larva of which is truly campodea-form and active. Beginning a sedentary life, however, in the egg-sac of a spider, it loses the use of its legs and the antennze become partly aborted, before the first moult. In Packard’s words, “ Owing to this change of hab- its and surroundings from those of its active ancestors, it changes its form, and the fully grown larva becomes cylin- drical, with small slender legs, and, owing to the partial disuse of its jaws, acquires a small, round head.” Meloide (Fig. 217) afford other excellent examples of the transition from the thysanuriform to the eruciform condition during the life of the individual. Thysanuriform characters become gradually suppressed in favor of the eruciform, until, in most of the highly developed orders (Mecoptera, Trichoptera, Lepidoptera, Diptera, Si- phonaptera and Hymenoptera), they cease to appear, except for a few embryonic traces an illustration of the principle of “acceleration in development.”’ Growth.—The larval period is pre-eminently one of growth. In Heterometabola, growth is continuous during the nymphal stage, but in Holometabola this important function becomes relegated to the larval stage, and pupal development takes place at the expense of a reserve supply of food accumulated by the larva. The rapidity of larval growth is remarkable. Trouvelot found that the caterpillar of Telea polyphemus attains in 56 days 4,140 times its original weight (1/20 grain), and has eaten an amount of food 86,000 times its primitive weight. Other larvz exceed even these figures; thus the maggot of a common flesh fly attains 200 times its original weight in 24 hours. Ecdysis.—The exoskeleton, unfitted for accommodating itself to the growth of the insect, is periodically shed, and along with it go not only such integumentary structures as hairs and scales, but also the chitinous lining, or intima, of DEVELOPMENT 165 the stomodzum, proctodzeum, trachez, integumentary glands, etc. The process of moulting, or ecdysis, 1n caterpillars is briefly as follows. The old skin becomes detached from the body by an intervening fluid of hypodermal origin; the skin dries, shrinks, is pushed backward by the contractions of the larva, and at length splits near the head, frequently under the neck; through this split appear the new head and thorax, and the old skin is worked back toward the tail until the larva is freed of its exruvie. The details of the process, however, are by no means simple. Ecdysis is probably something besides a provision for growth, for Collembola continue to moult long after growth has ceased, and the winged May fly sheds its skin once after emergence. The meaning of this is not known, though perhaps ecdysis has an excretory importance in the case of Collembola, which are exceptional among in- sects in having no Malpighian tubes. Number of Moults.—The frequency: of moulting differs greatly in different orders of insects. Acridiidz have five moults; Lepidoptera usually four or five, but often more, as in [sia (Pyrrharctia) isabella, which moults as many as ten times (Dyar); Musca domestica has three (Packard); the honey bee probably six (Cheshire); and the seventeen-year locust about twenty-five or thirty (Riley). Packard suggests that cold and lack of food during hibernation in arctians (as I. isabella) and partial starvation in the case of some beetles, cause a great number of moults by preventing growth, the hypodermis cells meanwhile retaining their activity. The appearance of the insect often changes greatly with each moult, particularly in caterpillars, in which the changes of coloration and armature may have some phylogenetic sig- nificance, as Weismann has attempted to show in the case of sphingid larve. Adaptations of Larve.—Larve exhibit innumerable con- formities of structure to environment. The greatest variety of adaptive structures occurs in the most active larve, such as predaceous forms, terrestrial or aquatic. These have well- 166 ENTOMOLOGY developed sense organs, excellent powers of locomotion, spe- cial protective and aggressive devices, etc. In insects as a whole, the environment of the larva or nymph and that of the adult are very different, as in the dragon fly or the butterfly, and the larvae are modified in a thousand ways for their own immediate advantage, without any direct reference to the needs of the imago. The chief purpose, so to speak, of the larva is to feed and grow, and the largest modifications of the larva depend upon nutrition. Take as one extreme, the legless, headless, fleshy and sluggish maggot, embedded 1n an abundance of food, and as the other extreme the active and “ wide-awake” larva of a carabid beetle, dependent for food upon its own powers of sensation, locomotion, prehension, etc., and obliged meanwhile to protect or defend itself. Between these extremes come such forms as caterpillars, active to a moderate degree. The great majority of larval characters, indeed, are correlated with food habits, directly or indirectly; directly in the case of the mouth parts, sensory and locomotor organs, and special struc- tures for obtaining special food; indirectly, as in respiratory adaptations and protective structures, these latter being numer- ous and varied. Larvee that live in concealment, as those that burrow in the ground or in plants, have few if any special protective struc- tures; active larvee, as-those of Carabide, have an armor-like integument, but owe their protection from enemies chiefly to their powers of locomotion and their aversion to light (nega- tive phototropism) ; various aquatic nymphs (Zaitha, Odonata ) are often coated with mud and therefore difficult to distin- guish so long as they do not move; caddis worms are con- cealed in their cases, and caterpillars are often sheltered in a leafy nest. There is no reason to suppose that insects conceal themselves consciously, however, and one is not warranted in speaking of an instinct for concealment in the case of insects— since everything goes to show that the propensity to hide, though advantageous indeed, is simply: a reflex, inevitable, DEVELOPMENT 167 negative reaction to light (negative phototropism) or a positive reaction to contact (positive thigmotropism). Exposed, sedentary larve, as those of many Lepidop- tera and Coleoptera, often exhibit highly developed protective adaptations. Caterpillars may be colored to match their sur- roundings and may resemble twigs, bird-dung, etc.; or larve may possess a disagreeable taste or repellent fluids or spines, these odious qualities being frequently associated with warn- ing colors. Larvee need protection also against adverse climatal condi- tions, especially low temperature and excessive moisture. The thick hairy clothing of some hibernating caterpillars, as Tsia (Pyrrharctia) isabella, doubtless serves to mollify sudden changes of temperature. Naked cutworms hibernate in well- sheltered situations, and the grubs of the common “ May beetles,’ or “ June bugs,’’ burrow down into the ground below the reach of frost. Ordinary high temperatures have little effect upon larvae, except to accelerate their growth. Exces- sive moisture is fatal to immature insects in general—conspicu- ously fatal to the chinch bug, Rocky Mountain locust, aphids and sawfly larve. The effect of moisture may be an indirect one, however; thus moisture may favor the development of bacteria and fungi, or a heavy rain may be disastrous not only by drowning larve, but also by washing them off their food plants. As a result of secondary adaptive modifications, larve may differ far more than their imagines. Thus Platygaster in its extraordinary first larval form (Fig. 218) is entirely unlike the larve of other parasitic Hymenoptera, reminding one, indeed, of the crustacean Cyclops rather than the larva of an insect. As Lubbock has said, the characters of a larva depend (1) upon the group of insects to which the larva belongs and (2) upon the special environment of the larva. Pupa.—The term pupa is strictly applicable to holometabo- lous insects only. Most Lepidoptera and many Diptera have an obtect pupa (Fig. 212), or one in which the appendages 168 ENTOMOLOGY and body are compactly united; as distinguished from the free pupa of Neuroptera, Trichoptera, Coleoptera and others, in which the appendages are free (Fig. 203). This distinction, however, cannot always be drawn sharply. Diptera present also the coarctate type ot pupa (Fig. 204), in which the pupa remains en- closed in the old larval skin, or pupa- rum. Pupal characters, though doubtless of great adaptive and phylogenetic signifi- Big. 212. cance, have received but little attention. Lepidopterous pupz present many puz- zling characters, for example, an eye- like structure (Fig. 213) suggesting | Obtect pupa of milk- an ancestral active condition, such as weed butterfly, Anosia still occurs among heterometabolous in- sects. Pupation of a Caterpillar.—The process of pupation in a caterpillar has been carefully observed by Riley. The cater- pillar of the milkweed butterfly (Pl. 1, 4) spins a mass of silk in which it entangles its suranal plate and anal prolegs and then hangs downward, bending up the anterior part of the body (B), which gradually becomes swollen. The skin of the caterpillar splits dorsally, from the head backward, and is worked back toward the tail (C and D) by the con- tortions of the larva. plexippus, natural size. Fic. 213. : E Head of chrysalis of The way in which the pupa becomes at- papitio polyxenes, to tached to its silken support-is rather com- a eye ee 5 : . ; nlarged. plex. Briefly, while the larval skin still retains its hold on the support, the posterior end of the pupa is withdrawn from the old integument and by the vigorous whirling and twisting of the body the hooks of the terminal cremaster of the pupa are entangled in the silken support. At first the pupa is elongate (£) and soft, but in an hour or so PAVE ele Successive stages in the pupation of the milkweed caterpillar, Anosia plexippus. Natural size. DEVELOPMENT 169 it has contracted, hardened, and assumed its characteristic form and coloration (fF). Pupal Respiration.—E xcept under special conditions, pup breathe by means of ordinary abdominal spiracles. Aquatic pupz -have special respiratory organs, such as the tracheal filaments of Simu- hum (Fig. 230), and the respiratory tubes of Culex (Fig. 229). Pupal Protection. — Inactive and helpless, most pupze are concealed in one way or another from the observation of enemies and are protected from mois- ture, sudden changes of temperature, mechanical shock and other adverse in- fluences. The larve of many moths burrow into the ground and make an . : e f Chryso da, earthen cell in which to pupate; a large Seeger ed eee ees ‘ after emergence of number of coleopterous larve (Lachno- imago. Slightly en- larged. sterna, Osmoderma, Passalus, Lucanus, etc.) make a chamber in earth or wood, the walls of the cell being strengthened with a cementing fluid or more or less silk, forming a rude cocoon. Silken cocoons are spun by some Neuroptera (Chrysopide, Fig. 214), by Trichoptera (whose cases are essentially cocoons), Lepidoptera, a few Co- leoptera (as Curculionidee, Donacia), some Diptera (as Cecido- myidz), Siphonaptera, and many Hymenoptera (for exam- ple, Tenthredinidze, Ichneumonide, wasps, bees and some ants). The cocoon-making instinct is most highly developed in Lepidoptera and the most elaborate cocoons are those of Satur- nid. The cocoon of Samia cecropia is a tough, water-proof structure and is double (Fig. 215), there being two air spaces around the pupa; thus the pupa is protected against moisture and sudden changes of temperature and from most birds as well, though the downy woodpecker not infrequently punc- tures the cocoon. S. cecropia binds its cocoon firmly to a 170 ENTOMOLOGY twig; Tropea luna and Telea polyphemus spin among leaves, and their cocoons (with some exceptions) fall to the ground; Callosamia promethea, whose coccon is covered with a curved leaf, fastens the leaf to the twig with a wrapping of silk, so that the leaf with its burden hangs to the twig throughout the winter. The leaves surrounding cocoons may render them inconspicuous or may serve merely as a foundation for the cocoon. While silk and often a water-proof gum or cement Bre 27 on Cocoon of Samia cecropia, cut open to skow the two silken layers and the enclosed pupa. Natural size. form the basis of a cocoon, much foreign material, such as bits of soil or wood, is often mixed in; the cocoons of many com- mon Arctiidae, as Diacrisia virginica and [sia isabella, consist principally of hairs, stripped from the body of the larva. Butterflies have discarded the cocoon, the last traces of which occur in Hesperiidz, which draw together a few leaves with a scanty supply of silk to make a flimsy substitute for a cocoon. Papilionid and pierid pupz are supported by a silken girdle (Fig. 27), and nymphalid chrysalides hang freely sus- pended by the tail (Fig. 212). Cocoon-Spinning.—The caterpillar of Telea polyphemus “feels with its head in all directions, to discover any leaves to which to attach the fibres that are to give form to the co- coon. If it finds the place suitable, it begins to wind a layer DEVELOPMENT We of silk around a twig, then a fibre is attached to a leaf near by, and by many times doubling this fibre and making it shorter every time, the leaf is made to approach the twig at the distance necessary to build the cocoon; two or three leaves are disposed like this one, and then fibres are spread between them in all directions, and soon the ovoid form of the cocoon distinctly appears. This seems to be the most difficult feat for the worm to accomplish, as after this the work is simply mechanical, the cocoon being made of regular layers of silk united by a gummy substance. The silk is distributed in zig- zag lines of about one-eighth of an inch long. When the cocoon is made, the worm will have moved his head to and fro, in order to distribute the silk, about two hundred and fifty-four thousand times. After about half a day’s work, the cocoon is so far completed that the worm can hardly be dis- tinguished through the fine texture of the wall; then a gummy resinous substance, sometimes of a light brown color, is spread over all the inside of the cocoon. ‘The larva continues to work for four or five days, hardly taking a few minutes of rest, and finally another coating is spun in the interior, when ETE) 216: the cocoon is all finished and completely air tight. The fibre diminishes in thick- ness as the completion of the cocoon advances, so that the last internal coat- ing is not half so thick and so strong as the outside ones.” (Trouvelot.) Emergence of Pupa.—Subterranean pupe wriggle their way to the surface Subterranean pupa of of the ground, often by the aid of spines Gee es (Fig. 216) that catch successively into the surrounding soil. These locomotor spines may occur on almost any part of the pupa, but occur commonly on the abdominal segments, as in lepidopterous pupz; the extremity of the abdomen, also, bears frequently one or more spinous projections, as in Tipulide, Carabidz and Lepidoptera, to assist the escape of the pupa. 172 ENTOMOLOGY These structures are found also in pupz, as those of Sesiide, that force their way out of the stems of plants in which the larve have lived. The emergence from the cocoon is accom- plished in some cases by the pupa, in others by the imago. Hemerobiide, Trichoptera and the primitive lepidopteron Eriocephala use the pupal mandibles to cut an opening in the cocoon; while many lepidopterous pupz have on the head a beak for piercing the cocoon, or teeth for rending or cutting the silk. Eclosion.—During the last few hours before the emer- gence of a butterfly the colors of the imago develop and may be seen through the transparent skin of the chrysalis (PI. 2, 4). No movement occurs, however, until several seconds before emergence; then, after a few convulsive movements of. the legs and thorax of the imprisoned insect, the pupa skin breaks in the region of the tongue and legs (B), a secondary split often occurs at the back of the thorax, and the butterfly emerges (C—E) with moist body, elongated abdomen and miniature wings. Hanging to the empty pupa case (Ff), or to some other available support, the insect dries and its wings eradually expand (G, H) through the pressure of the blood. At regular intervals the abdomen contracts and the wings fan the air, and sooner or later a drop or two of a dull greenish fluid (the meconium) is emitted from the alimentary canal. The expansion of the wings takes place rapidly, and in less than. an hour, as a rule, they have attained their full size (J). T. polyphemus is “ provided with two glands opening into the mouth, which secrete during the last few days of the pupa state, a fluid which is a dissolvent for the gum so firmly unit- ing the fibres of the cocoon. This liquid is composed in great part of bombycic acid. When the insect has accomplished the work of transformation which is going on under the pupa skin, it manifests a great activity, and soon the chrysalis cover- ing bursts open longitudinally upon the thorax; the head and legs are soon disengaged, and the acid fluid flows from its lle PAE from Anosia plexippus, d Successive stages in the emergence of the milkweed butterfly, Natural size, chrysalis. the DEVELOPMENT 73 mouth, wetting the inside of the cocoon. The process of ex- clusion from the cocoon lasts for as much as half an hour. The insect seems to be instinctively aware [?] that some time is required to dissolve the gum, as it does not make any attempt to open the fibres, and seems to wait with patience this event. When the liquid has fully penetrated the cocoon, the pupa con- tracts its body, and pressing the hinder end, which is furnished with little hooks, against the inside of the cocoon, forcibly extends its body; at the same time the head pushes hard upon the fibres and a little swelling is observed on the outside. These contractions and extensions of the body are repeated many times, and more fluid is added to soften the gum, until under these efforts the cocoon swells, and finally the fibres separate, and out comes the head of the moth. In an instant the legs are thrust out, and then the whole body appears; not a fibre has been broken, they have only been separated. “To observe these phenomena, | had cut open with a razor a small portion of a cocoon in which was a living chrysalis nearly ready to transform. The opening made was covered with a piece of mica, of the same shape as the aperture, and fixed to the cocoon with mastic so as to make it solid and air- tight; through the transparent mica, I could see the move- ments of the chrysalis perfectly well. “When the insect is out of the cocoon, it immediately seeks for a suitable place to attach its claws, so that the wings may hang down, and by their own weight aid the action of the fluids in developing and unfolding the very short and small pad-like wings. Every part of the insect on leaving the co- coon, is perfect and with the form and size of maturity, except the pad-like wings and swollen and elongated abdomen, which still gives the insect a worm-like appearance ; the abdomen con- tains the fluids which flow to the wings. “When the still immature moth has found a suitable place, it remains quiet for a few minutes, and then the wings are seen to grow very rapidly by the afflux of the fluids from the abdo- men. In about twenty minutes the wings attain their full WA ENTOMOLOGY size, but they are still like a piece of wet cloth, without con- sistency and firmness, and as yet entirely unfit for flight, but after one or two hours they become sufficiently stiff, assuming the beautiful form characteristic of the species.” (Trouvelot.) The expansion of the wing 1s due to blood-pressure brought about chiefly by the abdominal muscles. In the freshly- emerged insect, the two membranes of the wing are corru- gated, and expansion consists in the flattening out of these folds. The wing is a sac, which would tend to enlarge into a balloon-shaped bags were it not for hypodermal fibers which hold the wing-membranes closely together (Mayer). Samia cecropia also uses a dissolvent fluid; Tropea luna, Philosamia cynthia and others cut and force an opening through the cocoon by means of a pair of saw-like organs, one at the base of each front wing. Hypermetamorphosis.—In a few remarkable instances, metamorphosis involves more than three stages, owing to the existence of supernumerary larval forms. This phenomenon of hypermetamorphosis occurs notably in the coleopterous genera Meloe, Epicauta, Sitaris, Rhipiphorus and Stylops, in male Coccidze and several parasitic Hymenoptera. In Meloe, as described by Riley,, the newly-hatched larva (triungulin form) is active and campodea-form. , It climbs upon a flower and thence upon the body of a bee (Auntho- phora), which carries it to the nest, where it eats the egg of the bee. After a moult, the larva though still six-legged, has become cylindrical, fleshy and less active, resembling a lamelli- corn larva; it now appropriates the honey of the bee. With plenty of rich food at hand the larva becomes sluggish, and after another moult appears as a pseudo-pupa, with function- less mouth parts and atrophied legs. From this pseudo-pupa emerges a third larval form, of the pure eruciform type, fat and apodous like the bee-larvee themselves. After these four distinct stages the larva becomes a pupa and then a beetle. Epicauta, another meloid, has a similar history. The t7- ungulin (Fig. 217, d) of E. vittata burrows into an egg-pod DEVELOPMENT P5 of Melanoplus differentialis and eats the eggs of that grass- hopper. After a moult the second larva (carabidoid form) appears; this (B) is soft, with reduced legs and mouth parts and less active than the triungulin. A second moult and the scarabeidoid form of the second larva is assumed; the legs FiG. 217. Stages in the hypermetamorphosis of Epicauta. A, triungulin; B, carabidoid stage of second larva; C, ultimate stage of second larva; D, coarctate larva; E, pupa; F, imago. E is species cinerea; the others are vittata. All enlarged except F.—After Ritey, from Trans. St. Louis Acad. Science. and mouth parts are now rudimentary and the body more compact than before. A third and a fourth moult occur with little change in the form of the second larva, which is now in its ultimate stage (C). After the fifth moult, however, the coarctate larva, or pseudo-pupa, appears; this (D) hibernates and in spring sheds its skin and becomes the third larva, which soon transforms to a true pupa (£), from which the beetle (F) shortly emerges. Thus the pupal stage is preceded by at least three distinct larval stages. In the anomalous beetle Stylops, the males are winged, but the females are maggot-like and sedentary, living in the bodies of bees and wasps. Packard found as many as three hundred 176 ENTOMOLOGY triungulin larve issuing from a female Stylops in the body of an dAndrena. The further life history of Stylops is but im- perfectly known; probably the triungulin climbs upon a bee or a wasp and enters its body, after the manner of the Euro- pean Rhipiphorus paradoxus, whose life-history is much bet- ter understood. The most extraordinary metamorphoses have been found among parasitic Hymenoptera, as in Platygaster, a proctotry- pid which infests the larva of Cecidomyia. ‘The egg of Platy- gaster, according to Ganin, hatches into a larva of bizarre <2 Ps A or x fc yay fee Stages in the hypermetamorphosis of Platygaster. A, first larva; B, second larva; C, third larva; a, antenna; b, brain; f, fat-tissue; h, hind intestine; m, mandible; mo, mouth; ms, muscle; n, nerve cord; r, reproductive organ of one side; s, salivary gland; t, trachea.—After GANIN. form (Fig. 218, 4), suggesting the crustacean Cyclops, rather than an insect. ‘This first larva has a blind food canal and no nervous, circulatory or respiratory systems. After a moult the outline is oval (6), and there are no appendages as yet, though the nervous system is partially developed. Another moult, and the third larva appears (C), elliptical in contour, externally segmented, with trachez and a pair of mandibles. DEVELOPMENT 177 From now on, the development is essentially like that of other parasitic Hymenoptera. Equally anomalous are the changes undergone by Poly- nema, a proctotrypid parasite in the eggs of dragon flies, and by the proctotrypid Teleas, which affects the eggs of the tree cricket (Gicanthus). In all these cases the larvee go through changes which in most other insects are confined to the egg stage. In other words, the larva hatches before its embryonic development is completed, so to speak. Significance of Metamorphosis.—* The essential features of metamorphosis,” says Sharp, ‘‘ appear to be the separation in time of growth and development, and the limitation of the reproductive processes to a short period at the end of the indi- vidual life.” The simplest insects, Thysanura, have no metamorphosis, and show no traces of ever having had one. Hence it is in- ferred that the first insects had none; in other words, the phe- nomenon of metamorphosis originated later than insects them- selves. Successive stages in the evolution of metamorphosis are illustrated in the various orders of insects. The distinctive mark of the simplest metamorphosis, as in Orthoptera and Hemiptera, is the acquisition of wings; growth and sexual development proceeding essentially as in the non- metamorphic insects (Thysanura and Collembola). Here the development of wings does not interfere with the activity of the insect; its food habits remain unaltered; throughout life the environment of the individual is practically the same. Even when considerable difference exists between the nym- phal and imaginal environments, as in Ephemerida and Odonata, the activity of the individual may still be continu- ous, even if somewhat lessened as the period of transforma- tion approaches. With Neuroptera, the pupal stage appears. In these and all other holometabolous insects the larva accumulates a sur- plus of nutriment sufficient for the further development, which becomes condensed into a single pupal stage, during which external activity ceases temporarily. 13 178 ENTOMOLOGY With the increasing contrast between the organization of the larva and that of the imago, the pupal stage gradually becomes a necessity. Metamorphosis now means more than the mere acquisition of wings, for the larva and the imago have become adapted to widely different environments, chiefly as regards food. The caterpillar has biting mouth parts for eating leaves, while the adult has sucking organs for obtaining liquid nourishment; the maggot, surrounded by food that may be obtained almost without exertion, has but minimum sensory and locomotor powers and for mouth parts only a pair of simple jaws; as contrasted with the fly, which has wings, highly developed mouth parts and sense organs, and many other adaptations for an environment which is strikingly un- like that of the larva; so also in the case of the higher Hymen- optera, where maternal or family care is responsible for the helpless condition of the larva. Thus it is evident that the change from larval to imaginal adaptations is no longer congruous with continuous external activity; a quiescent period of reconstruction becomes in- evitable. As was said, the eruciform type of larva has been derived from the thysanuriform type, the strongest evidence of this being the fact that among hypermetamorphic insects, the change from the one to the other takes place during the life- time of the individual. Furthermore, the eruciform condi- tion is plainly an adaptive one, brought about by an abundant and easily obtainable supply of food. The lack of a thysa- nuriform stage in the development of the most specialized eruciform larve, as those of flies and bees, is regarded by Hyatt and Arms as an illustration of the general principle known as “acceleration of development,” according to which newer and useful adaptive characters tend to appear earlier and earlier in the development, gradually crowding upon and forcing out older and useless characters. In connection with. this subject, the appearance of temporary abdominal legs in embryo bees is significant, as indicating an ancestral active DEVELOPMENT 179 condition. In accounting for the evolution of metamorpho- sis, the theory of natural selection finds one of its most important appli- Fic. 210. cations. 3. INTERNAL METAMORPHOSES In Heterometabola, the internal post-embryonic changes are as di- mette as the external changes of form; in Holometabola, on the con- trary,. not all the larval organs ; : ; J Diagrammatic transverse pass directly into imaginal organs, — section of Corethra larva, to show imaginal buds of wings (w) and legs (/); h, hypoder- molished and their substance recon- ™!5; # integumerft.—Modified from Lang’s Lehrbuch. fom certain larval ‘tissues are de- structed into imaginal tissues. When Fic. 220. Diagrammatic transverse sections of muscid larve, to show imaginal buds. hi, lar- val hypodermis; 7, larval integument; if, imaginal hypodermis; /, imaginal bud of leg; w, imaginal bud of wing.—Modified from Lang’s Lehrbuch. 180 ENTOMOLOGY indirect, however, the internal metamorphosis is nevertheless continuous and gradual, without the abruptness that charac- terizes the external transformation. In the larval stage ima- ginal organs arise and grow; in the pupal stage the purely larval organs gradually disappear while the imaginal organs are continuing their development. Imaginal buds of full grown larva of Pieris, dorsal aspect. b, brain; m, mid intestine; st, prothoracic spiracle; s+, first abdominal spiracle; sg, silk gland; J, prothoracie bud; II, bud of fore wing; JIJ, bud of hind wing.—After Gonin. Phagocytes.—The destruc- tion of larval tissues, or /is- tolysis, is due often to the amoeboid blood corpuscles, known as leucocytes or phago- cytes, which attack some tis- sues and absorb their mate- rial, but later are themselves food for the developing imagi- nal tissues. The construction of tissues is termed /isto- genesis. In Coleoptera, however, the degeneration of the larval mus- cles is entirely chemical, there being no evidence of phago- cytosis, according to Dr. R. S. Breed. Berlese, indeed, goes so far as to deny in general the destructive action of leuco- cytes on larval tissues. Imaginal Buds.—The wings and legs of a fly originate in the larva in the form of cellu- lar masses, or imaginal buds, as Weismann discovered. Thus in the larva of Corethra, there are in each thoracic segment a pair of dorsal buds and a pair of ventral buds (Fig. 219), each bud being clearly an evagi- nation of the hypodermis at the bottom of a previous invagi- DEVELOPMENT ISI nation. The six ventral buds form the legs eventually; of the dorsal buds, the middle and posterior pairs form, respec- tively, the wings and the halteres, and the anterior pair form the pupal respiratory processes. Each imaginal bud is situ- ated in a peripodal cavity, the wall of which (peripodal mem- brane) 1s continuous with the general hypodermis; as the legs and wings develop, they emerge from their peripodal sacs and become free. In Corethra but little histolysis occurs, most of the larval structures passing directly into the corresponding structures of the adult. Corcethra, indeed, is in many respects interme- diate between heterometabolous and holometabolous insects as regards its internal changes. lo a 4 ria pS Section through left hind wing in larva of Pieris rape, the section being a frontal one of the caterpillar; the base of the wing is anterior in position,. and the apex posterior. c, cuticula; h, hypodermis; t, trachea; w, developing wing.—After Mayer. Muscidz.—In Muscide, as compared with Corethra, the imaginal buds are more deeply situated, the peripodal mem- brane forming a stalk (Fig. 220), and the processes of his- tolysis and histogenesis become extremely complicated. The hypodermis, muscles, alimentary canal and fat-body are grad- ually broken down and remodeled, and part of the respiratory system is reorganized, though the dorsal vessel and the central nervous system, uninterrupted in their functions, undergo comparatively little alteration. The imaginal hypodermis of the thorax arises from thick- 182 ENTOMOLOGY enings of the peripodal membrane which spread over the lar- Internal transformations of Sphinx ligus- im. A, larva Be pupasiG an, antenna; b, brain; f, fore intestine; fr, food reservoir; hi, hind intestine: ht, heart; m, mid intestine; mt, Malpighian tubes; p/p, lion; t, testis; tg, thoracic ganglia; v, ven- tral nerve cord.—After NEwport. moth; a, aorta; proboscis; s, frontal section of the larva appearing as in Fig. subeesophageal gang- while the latter is gradually being broken down by the leuco- cytes; in the head and abdo- val hypodermis, men the process is essen- tially the same as in the thorax, the new hypodermis arising from imaginal buds. Most of the larval mus- cles, excepting the “titeee pairs of respiratory muscles, undergo dissolution. The imaginal muscles have been traced back to mesodermal cells such as are always as- sociated with imaginal buds. Hymenoptera and Lepi- doptera.—The internal transformation in Hymen- optera, according to Bugn- profound than more ex- ion, 1s less in Muscide and tensive than in Coleoptera and Lepidoptera. The metamorphosis in resembles in in- ternal Lepidoptera many respects that of Core- thra. In both these orders the dorsal pair of protho- In a full-grown the fundaments of the imaginal legs ‘and wings (Fig. 221) racic buds is absent. caterpillar may be seen, the wings in a Many ZOD ame DEVELOPMENT 183 of the details of the internal metamorphosis in Lepidoptera have been described by Newport and Gonin. Figure 223, after Newport, shows some of the more evident internal dif- ferences in the larva, pupa and imago of a lepidopterous insect. Significance of Pupal Stage.—To repeat—among holo- metabolous insects the function of nutrition becomes relegated to the larval stage and that of reproduction to the imaginal stage. Larva and imago become adapted to widely different environments. So dissimilar are the two environments that a gradual change from the one to the other 1s no longer pos- sible; the revolutionary changes in structure necessitate a tem- porary cessation of external activity. GEAGE Pie aay: ADAPTATIONS OF AQUATIC INSECTS Ease, versatility and perfection of adaptation are beauti- fully exemplified in aquatic insects. Systematic Position.—Aquatic insects do not form a sepa- rate group in the system of classification, but are distributed among many orders, of which Plecoptera, Ephemerida, Odo- nata and Trichoptera are pre-eminently aquatic. One third of the families of Heteroptera and less than one fourth those of Diptera are more or less aquatic. One tenth of the families of Coleoptera frequent the water at one stage or another, but only half a dozen genera of Lepidoptera. A few Collembola live upon the surface of water, and several Hymenoptera, though not strictly aquatic, are known to parasitize the eggs and larvee of aquatic insects. The change from the terrestrial to the aquatic habit has been a gradual change of adaptation, not an abrupt one. Thus at present there are some tipulid larve that inhabit comparatively dry soil; others live in earth that is moist; many require a saturated soil near a body of water and many, at length, are strictly aquatic. Among beetles, also, similar transitional stages are to be found. Food.—Insects have become adapted to utilize with re- markable success the immense and varied supply of food that the water affords. Hosts of them attack such parts of plants as project above the surface of the water, and the caterpillar of Paraponyx (Fig. 171) feeds on submerged leaves, espe- cially of Vallisneria, being in this respect unique among Lepi- doptera. Hydrophilid beetles and many other aquatic insects devour submerged vegetation. The larve of the chrysomelid genus Donacia find both nourishment and air in the roots of aquatic plants. Various Collembola subsist on floating alge, 184 ADAPTATIONS OF AQUATIC INSECTS 185 and larvze of mosquitoes and black-flies on microscopic organ- ismS near the surface, while larve of Chironomus find food in the sediment that accumulates at the bottom of a body of water. Predaceous species abound in the water. Notonecta (Fig. 224) approaches its prey from beneath, clasps it with the front Fic. 224. / N \ Backswimmer, Notonecta insulata, Water-skater, Gerris remigis, natural size. natural size. pair of legs and pierces it. Nepa and Ranatra likewise have prehensile front legs along with powerful piercing organs. Belostoma and Benacus (Vig. 22) even kill small fishes by their poisonous punc- tures. Some other kinds, as the water- skaters (Gerride, Fig. 225), depend on dead or disabled insects. The species of Hydrophilus (Fig. 226) are to some ex- tent carnivorous as larve but phytopha- gous as imagines, while Dytiscidze are car- nivorous throughout life. Aquatic insects eat not only other insects, but also worms, crustaceans, mollusks or any other avail- able animal matter. Even aquatic insects are not exempt from the attacks of parasitic species. A few Hymenoptera actually enter the Fic. 226. Hydrophilus triangularis, natural size. water to find their victims, for example, the ichneumon A grio- typus, which lays its eggs on the larve of caddis flies. 186 ENTOMOLOGY Locomotion.—Excellent adaptations for aquatic locomo- tion are found in the common Hydrophilus triangularis (Fig. 226). Its general form reminds one of a boat, and its long legs resemble oars. The smoothly elliptical contour and the polished surface serve to lessen friction. Owing to the form of the body (Fig. 227, 4) and the presence of a dorsal air- A . B ‘Transverse sections of (4) Hydrophilus and (B) Notonecta. e, elytron; h, hemely- tron; 7, metathoracic leg. chamber under the elytra, the back of the insect tends to re- main uppermost, while in Notonecta (Fig. 227, B), on the other hand, the conditions are reversed, and the insect swims with its back downward. The legs of Hydrophilus, excepting the first pair, are broad and thin (Fig. 228, 4) and the tarsi are fringed with long hairs. When swimming, the “ stroke ”’ is made by the flat surface, aided by the spreading hairs; but on the “ recover,” the leg is turned so as to cut the water, while the hairs fall back against the tarsus from the resistance of the water, as the leg is being drawn forward. The hind legs, being nearest the center of gravity, are of most use in swim- ming, though the second pair also are used for this purpose; indeed, a terrestrial insect, finding itself in the water, instinc- tively relies upon the third pair of legs for locomotion. Hy- drophilus uses its oar-like legs alternately, in much the same sequence as land insects, but Cybister.and other Dytiscide, which are even better adapted than Hydrophilus for aquatic locomotion, move the hind legs simultaneously, and therefore can swim in a straight line, without the wobbling and less economical movements that characterize Hydrophilus. ADAPTATIONS OF AQUATIC INSECTS 187 Larve of mosquitoes propel themselves by means of lash- ing, or undulatory, movements of the abdomen. A peculiar mode of locomotion is. found in dragon fly nymphs, which project themselves by forcibly ejecting a stream of water from the anus. On account of the large amount of air that they carry about, most aquatic imagines are lighter than the water in which they Left hind legs of aquatic beetles. A, Hydrophilus triangularis; B, Cybister fimbrio- latus; c, coxa; f, femur; s, spur; t, tarsus; fi, tibia; tr, trochanter. live, and therefore can rise without effort, but can descend only by exertion, and can remain below only by clinging to chance stationary objects. The mosquito larva (Fig. 229, 4) is often heavier than water, but the pupa (Fig. 229, B) is lighter, and remains clinging to the surface film. . The tension of this surface film is sufficient to support the weight of an insect up to a certain limit, provided the insect 188 ENTOMOLOGY has some means of keeping its body dry. This is accom- plished usually by hairs, set together so thickly that water cannot penetrate between them. As the legs and body of Gerris are rendered water-proof by a vel- Fic. 220. vety clothing of hairs, the insect, though heavier than water, is able to skate about on the surface. Gyrinus, by means of a similar - adaptation, can circle about on the surface film, and minute collem- bolans leap about on the surface as readily as on land. The modifications of the legs for swimming have often impaired their usefulness for walking, so that many aquatic Coleoptera and Hemiptera can move but awk- wardly on land. When walking, it is interesting to note, Cybister and some other aquatic forms no longer move their hind legs simul- taneously as they do in swimming, but use them alternately, like ter- restrial species. The adaptations for swimming do not necessarily affect the power of flight. Dytiscus, Hydrophilus, Gyrinus, Notonecta, Benacus and many other Coleoptera and Hemip- Ht MAAN RST ruee: CEN: dos tera leave the water at night and mosquito, Culex pipiens. r, respi fly around, often being found about ratory tube; t, tracheal gills. Gees tens Respiration.—Aquatic insects have not only retained the primitive, or open (holopneustic), type of respiration, charac- ADAPTATIONS OF AQUATIC INSECTS 189 terized by the presence of spiracles, but have also developed an adaptive, or closed (apneustic), type, for utilizing air that is mixed with water. Through minor modifications of structure and habit, many holopneustic insects have become fitted for an aquatic life. In these instances the insects have some means of carrying down a supply of air from the surface of the water. Thus Noto- necta bears on its body a silvery film of air entangled in closely set hairs, which exclude the water. Gyrinus descends with a bubble of air at the end of the abdomen. Dytiscus and Hy- drophilus have each a capacious air-space between the elytra and the abdomen, into which space the spiracles open. Nepa and Ranatra have each a long respiratory organ composed of two valves, which lock together to form a tube that communicates with the single pair of spiracles situated near the end of the abdomen. The mosquito larva, hanging from the surface film, breathes through a cylindrical tube (Fig. 229, A, 7) pro- jecting from the penultimate abdominal segment; the pupa, however, bears a pair of respiratory tubes on the back of the thorax (Fig. 229, B, r, r), which is now upward, probably in order to facilitate the escape of the fly. The rat-tailed maggot (Eristalis), three quarters of an inch long, has an extensile caudal tube seven times that length, containing two trachez terminating in spiracles, through which air is brought down from above the mud in which the larva lives. Similarly, in the dipterous larva, Bittacomorpha clavipes (Fig. 172), the posterior segments of the abdomen are attenuated to form a long respiratory tube. The larva of Donacia appears to have no special adaptations for aquatic respiration except a pair of spines near the end of the body, for piercing air chambers in the roots of the aquatic plants in which it dwells. The simplest kind of apneustic respiration occurs in aquatic nymphs such as those of Ephemerida and Agrionide, whose skin at first is thin enough to allow a direct aération of the blood. This cutaneous respiration is possible during the early life of many aquatic species. 190 ENTOMOLOGY Branchial respiration, however, is the prevalent type among aquatic nymphs and is perhaps the most important of their adaptive characteristics. Thin-walled and extensive out- . growths of the integument, containing tracheal branches or, rarely, only blood, enable these forms to obtain air from the water. May fly nymphs (Figs. 19, 4; 169), with their ample waving gills, offer familiar examples of branchial respiration. Tracheal gills are very diverse in form and situation, occurring in a few species of May fly nymphs on the Fic. 230. thorax or head, though commonly re- stricted to the sides of the abdomen, where they occur in pairs or in paired clusters (Fig. 19, 4). Caudal gills are found in agrionid nymphs (Fig. 170). The aquatic caterpillars of Paraponyx (Fig. 171) are unique among Lepidop- tera in having gills, which are filamentous in this instance. Caddis worms, enclosed in their cases, maintain a current of water by means of undulatory movements of the body, Simulium; A, larva; B, and the larvee and pupz of most black flies pupa, showing respira- tory filaments. (Simuliide, Fig. 230) secure a continuous supply of fresh air simply by fastening themselves to rocks in swiftly flowing streams. Rectal respiration is highly developed in odonate and ephe- merid nymphs. In thesé, the rectum is lined with thousands of tracheal branches, which are bathed by water drawn in from behind, and then expelled. All these kinds of respiration—cutaneous, branchial and occur in young ephemerid nymphs; while mosquito rectal larvee have in addition spiracular respiration. With the arrival of imaginal life, tracheal gills disappear, except in Perlida, and even in these insects the gills are of little if any use. Marine Insects.—Except along the shore, the sea is almost ADAPTATIONS OF AQUATIC INSECTS IO! devoid of insect life, the exceptions being a few chironomid larvee which have been dredged in deep water, and fifteen species of Halobates (belonging to the same family as our familiar pond-skaters ), which are found on warm smooth seas, where they subsist on floating animal remains. Between tide-marks may be found various beetles and col- lembolans, which feed upon organic debris; as the tide rises, the former retreat, but the latter commonly burrow in the sand or under stones and become submerged, for example the com- mon Anurida maritima. Insect Drift.—Seaweed or other refuse cast upon the shore harbors a great variety of insects, especially dipterous larve, staphylinid scavengers and predaceous Carabide. On the shores of inland ponds and lakes a similar assemblage of in- sects may be found feeding for the most part on the remains of plants or animals, or else on one another. During a strong wind, the leeward shore of a lake is an excellent collecting ground, as many insects are driven against it. On the shores of the Great Lakes insects are occasionally cast up in immense numbers, forming a broad windrow, fifty or perhaps a hundred miles long. Needham has described such an occurrence on the west shore of Lake Michigan, following a gale from the northeast. In this instance, a liter of the drift contained nearly four thousand insects, of which 66 per cent. were crick- ets (Nemobius), 20 per cent. Acridiidz, and the remainder mostly beetles (Carabidz, Scarabeeide, Chrysomelidz, Coc- cinellidz, etc.), dragon flies, moths, butterflies (Anosia, Pieris, etc.) and various Hemiptera, Hymenoptera and Dip- tera. A large proportion of the insects were aquatic forms, such as Hydrophilus, Cybister, Zaitha, and a species of caddis fly; these had doubtless been carried out by freshets, while the butterflies and dragon flies had been borne out by a strong wind from the northwest, after which all were driven back to the coast by a northeast wind. While some of these insects survived, notably Coccinellide, Trichoptera, Asilidae, Acridi- idee and Gryllidz, nearly all the rest were dead or dying, in- 192 ENTOMOLOGY cluding the dragon flies, flies, bumble bees and wasps. Fora- ging Carabidz were observed in large numbers, also scaven- gers of the families Staphylinidz, Silphidee and Dermestide. On the seashore and on the shores of the Great Lakes, the salient features of insect life are essentially the same. Sim- ilar species occur in the two places with similar biological relations, on account of the general similarity of environment. Origin of the Aquatic Habit.—The theory that terrestrial insects have arisen from aquatic species is no longer tenable, for the evidence shows that the terrestrial type is the more primitive. Aquatic insects still retain the terrestrial type of organization, which remains unobscured by the temporary and comparatively slight adaptations for an aquatic life. Thus, the development of tracheal gills has involved no important modification of the fundamental plan of tracheal respiration. It is significant, moreover, that the most generalized, or most primitive, insects—Thysanura—are without exception terres- trial. Aquatic insects do not constitute a phylogenetic unit, but represent various orders, which are for the most part un- doubtedly terrestrial, notwithstanding the fact that a few of these orders (Plecoptera, Ephemerida, Odonata, Trichoptera ) are now wholly aquatic in habit. Adaptations for an aquatic existence have arisen independently and often, in the most diverse orders of insects. Grae RaiRARe: WV COLOR AND COLORATION The naturalist distinguishes between the terms color and coloration. A color is a single hue, while coloration refers to the arrangement of colors. Sources of Color.—The colors of insects are classed as (1) pigmental (chemical), those due to internal pigments; (2) structural (physical), those due to structures that cause interference or reflection of light; and (3) combination colors (chemico-physical), which are produced in both ways at once. Structural Colors.—The iridescence of a fly’s wing and that of a soap bubble are produced in essentially the same way. The wing, however, consists of two thin, transparent, slightly separated lamellz, which diffract white light into prismatic rays, the color differences depending upon differences in the distance between the two membranes. The brilliant iridescent hues of many butterfly scales are due to the diffraction of light by fine, closely parallel striz (Fig. g2) just as in the case of the “ diffraction gratings ’’ used by the physicist, which consist of a glass or metallic plate with parallel diamond rulings of microscopic fineness. The par- ticular color produced depends in both cases upon the distance between the striz. Though almost all lepidopterous scales are striated, it is only now and then that the striz are sufficiently close together to give diffraction colors. Ina Brazilian species of Apatura the iridescent scales have 1050 striz to the milli- meter, and in a species of Morpho, according to Kellogg, the iridescent pigmented scales have 1,400 strize per millimeter, the strize being only .0007 mm. apart; while in some of the finest Rowland gratings they are as far apart as .oo15 mm., though numbering 1,700 per millimeter. These interference colors of butterfly scales may be due, not 14 193 194 ENTOMOLOGY only to surface markings, but also to the lamination of the scale and to the overlapping of two or more scales. In beetles the metallic blues and greens, and iridescence in general, are often produced by minute lines or pits that diffract the light. Purely structural colors, however, are not so common as might be supposed, according to Tower, who says, “ The pits alone, however, are powerless to produce any color; it is only when they are combined with a highly reflecting and refractive sur- face lamella and a pigmented layer below that the iridescent color appears. The action of light is in this case the same as in the plain metallic coloring, excepting that each pit acts as a revolving prism to disperse different wave-lengths of light in different directions, and the combined result is iridescence. The existence of minute pits over the body surface is of com- mon occurrence, but it is only when they are combined as above that iridescent colors occur.” Silvery white effects are usually caused by the total reflec- tion of light from scales or other sacs that are filled with air; the same silvery appearance is given also by air-filled trachez and by the air bubbles that many aquatic insects carry about under water. Violet, blue-green, coppery, silver and gold colors are, with few exceptions, structural colors. (Mayer.) Pigmental Colors.—These are either cuticular or hypo- dermal. The predominant brown and black colors of insects are made by pigment diffused in the outer layer of the cuticula (Fig. 88). Cockroaches are almost white just after a moult, but soon become brown, and many beetles change gradually from brown to black. In these cases it is apparently signifi- cant that the cuticular pigments lie close to the surface of the skin, 1. e., where they are most exposed to atmospheric influences. Tower finds, however, that cuticular colors “ are not due to drying, oxidation, secretion, or like processes,” but are due to “some katalytic agent or enzyme [formed by the hypodermis|] which, passing out through the pore canals, comes in contact with the primary cuticula and there becomes the active factor in the production of cuticula colors.” COLOR AND COLORATION 195 The cuticular pigments are derived, of course, from the underlying hypodermis cells, and these cells themselves, more- over, usually contain (1) colored granules or fatty drops which give red, yellow, orange and sometimes white or gold colors as seen through the skin; (2) diffused chlorophyll (green) or xanthophyll (yellow), taken from the food plant. Unlike the structural colors, which are persistent, these hypo- dermal colors often change after death, though less rapidly when the pigments are tightly enclosed, as in scales or hairs. Though white and green are structural colors as a rule, they are due to pigments in Pieridz, Lycznidze and some Geometridee. Frequently a color pattern consists partly of cuticular and partly of hypodermal colors, the hypodermal or sub-hypoder- mal color forming “a groundwork upon which the pattern is cut out by the cuticular color.” (Tower.) Thus in Leptino- tarsa decemlineata the pattern “is composed of a dark cutic- ular pigment upon a yellow hypodermal background.” Combination Colors.—The splendid changeable hues of Apatura, Euplea and other tropical butterflies depend upon the fact that their scales are both pigmented and striated. Under the microscope, certain Apatura scales are brown by transmitted light and violet by reflected light, and to the un- aided eye the color of the wing is either brown or violet, ac- cording as the light is received respectively from the pigment or from the striated surfaces of the scales. According to Tower, chemico-physical colors “which are of exceedingly wide occurrence, are also the most brilliant and varied of all those found in insects. To this class belong all metallic, iri- descent, pearly, and translucent colors, as well as blue, green, and violet in almost every case.”’ Nature of Pigments.—Some pigments are taken bodily from the food; others are manufactured indirectly from the food, and some of these are excretory products. The green color of many caterpillars and grasshoppers is due to chlorophyll, which tinges the blood and shows through 196 ENTOMOLOGY the transparent integument. Mayer has found that scales of Lepidoptera contain only blood while the pigment is forming; that the first color to appear upon the pupal wings is a dull ochre or drab—the same color that the blood assumes when it is removed from the pupa and exposed to the air; also that pigments like those of the wings may be manufactured artifi- cially from pupal blood. Pieridze are peculiar in the nature of their pigments, as Hopkins has shown. The white pigment of this family is uric acid and the reds and yellows of Pieris, Colias and Papilio are due to derivatives of uric acid; the yellow pigment, termed lepidotic acid, precedes the red in time of appearance, the latter being probably a derivative of the former. The green pigments of some Papilionide, Noctu- idee, Geometridz and Sphingidz are also said by some inves- tigators to be products of uric acid, which in insects as in other animals is primarily an excretory, or waste, product. Effects of Food on Color.—Besides chlorophyll, to which various caterpillars, aphids and other forms owe their green color, the yellow constituent of chlorophyll, namely xantho- phyll, frequently imparts its color to plant-eating insects, while some phytophagous species are dull yellow or brown from the presence of tannin, taken from the food plant. Most pig- ments, however, are elaborated from the food by chemical processes that are not well understood. Many who have reared Lepidoptera extensively know that the color of the imago is influenced by the character of the larval food, other conditions being equal, and are able at will to effect certain color changes simply by feeding the larvee from birth upon particular kinds of plants. In this country we have few observations upon the subject, but in Europe the effects of food upon coloration have been ascertained in the case of many species of Lepidoptera. According to Greg- son, Hybernia defoliaria is richly colored when fed upon birch, but is dull colored and almost unmarked when fed on elm. Pictet, by feeding larve of Vanessa urtice on the flow- ers instead of the leaves of the nettle obtained the variety COLOR AND COLORATION 197 known as urticoides. Food affects the color of the larva also, as Poulton found in the case of caterpillars of Tryphena pro- nuba, all from the same batch of eggs. When fed with only the white midribs of cabbage leaves, the larvae remained almost white for a time, but afterward showed a moderate amount of black pigment; when fed with the yellow etiolated heart-leaves or the dark green external leaves, however, the larvz all be- came bright green or brown—the same pigment being derived indifferently from etiolin (probably the same substance as xanthophyll) or chlorophyll. Though the pigments may differ in color or amount accord- ing to the kind of food, the color patterns vary without regard to food. Thus Callosamia promethea, Leptinotarsa decem- lineata (Colorado potato beetle), Coccinellidee (lady-bird beetles) and a host of other insects exhibit extensive individ- ual variations in coloration under precisely the same food con- ditions. Caterpillars of the same kind and age are often very differently marked when feeding upon the same plant; for example, Heliothis armiger (corn worm) and the sphingid Deilephila lineata. Furthermore, striking changes of colora- tion accompany each moult in most caterpillars, but particu- larly those of butterflies, and these changes may prove to have an important phylogenetic significance. Individual differ- ences of coloration apart from those due to the direct action of food, light, temperature and other environmental condi- tions are to be explained by heredity. Effects of Light and Darkness.—Sunlight is an important factor in the development of most animal pigments, as they will not develop in its absence. The collembolan Anurida maritima is white at hatching, but soon becomes indigo blue, unless shielded from sunlight, in which event it remains white until exposed to the sunlight, when it assumes the blue color. Subterranean or wood-boring larve are commonly white or yellow, but never highly colored. The most notable instances, however, are furnished by cave insects. These, like other cavernicolous animals, are characteristically white or pale 198 ENTOMOLOGY from the absence of pigment, if they live in regions of con- tinual darkness, but have more or less pigmentation in propor- tion respectively to the greater or less amount of sunlight to which they have access. Curiously enough, light often hastens the destruction of pigment in insects that are no longer alive, for which reason it is necessary to keep cabinet specimens in the dark as much as possible. Life is evidently essential for the sustension or renewal of the pigments. A chrysalis not infrequently matches its surroundings in color. This phenomenon has been investigated by Poulton, who has proved that the color of the chrysalis is determined largely by the prevalent color of the surroundings during the last few days of larval life. Larve of Pieris rape, raised upon the same food plant (all other conditions being made as nearly equal as possible) produced dark pupze if kept in dark- ness for a few days just before pupation; yellow light arrested the formation of the dark pigment and gave green pupz ; while light colors in general gave light-colored pupe. This color re- semblance is commonly assumed to be of protective value, and perhaps it is. Nevertheless, it is a direct effect of light, and does not need to be explained by natural selection, even though it cannot be denied that natural selection may have helped in its production. Poulton extended his studies to the adaptive coloration of caterpillars and has published the results of an extensive series of experiments which prove that the colors of certain caterpillars also are directly produced by the same colors in the surrounding light. Gastropacha quercifolia, which always rests by day on the older wood of its food plant, was given black twigs, reddish brown sticks, lichens, etc., to rest upon, and though all the larvee were from the same cluster of eggs, and had been fed in the same way, each larva gradually assumed the color or colors of its resting place, resulting in exquisite examples of protective resemblance, the most re- markable of which were those in which the larve assumed the COLOR AND COLORATION 199 variegated coloration of lichens. Only the younger larve, however, proved to be susceptible to the colors of the environ- ment; unlike those of Amp/idasis betularia, in which the older larve also were sensitive to the surrounding light. Here again, natural selection is unnecessary, even if not superfluous, as an explanation of this kind of protective coloration. Effects of Temperature.—The amount of a pigment in the wing of a butterfly depends in great measure upon the sur- rounding temperature during the pupal stage, when the pig- ments are forming. Black or brown spots have been enlarged artificially by subjecting chrysalides to cold; hence it is probable that the characteristically large black spots on the under side of the wings of the spring brood of our Cyaniris pseudargiolus are simply a direct effect of cold upon the wintering chrysal- ides. Similarly the spring brood (variety marcia) of Phy- ciodes tharos owes its distinctive coloration to cold, as Ed- wards has proved experimentally. Lepidoptera have been the subject of very many temperature experiments, some of which will be mentioned presently in the consideration of seasonal coloration. Speaking generally, warmth (except in melanism) tends to induce a brightening and cold a darkening of coloration, the darkening being due to an increased amount of black or brown pigment. ‘Temperature, whether high or low, seldom if ever produces new pigments, but simply alters the amount and dis- tribution of pigments that are present already. Effects of Moisture.—Very little is known as to the effects of moisture upon coloration. The dark colors of insular or coastal insects as contrasted with inland forms, and the pre- dominance of dull or suffused species in mountainous regions of high humidity, have led observers occasionally to ascribe melanism and suffusion to humidity. In these cases, how- ever, the possible influence of low temperature and other fac- tors must be taken into consideration. The experiments of Merrifield and of Standfuss showed no effect of moisture upon lepidopterous pupe. 200 EN TOMOLOGY Pictet has recently found, however, that humidity acting on the caterpillars of Vanessa urtice and V. polychloros has a conspicuous effect on the coloration of the butterflies. Thus when the caterpillars were fed for ten days with moist leaves, the resulting butterflies had abnormal black markings on the wings, and the same results followed when the larvze were kept in an atmosphere saturated with moisture. Climatal Coloration.—The brilliant and varied colors of tropical insects are popularly ascribed to intense heat, light and moisture; and the dull monotonous colors of arctic insects, similarly, to the surrounding climatal conditions. Climate undoubtedly exerts a strong influence upon coloration, but the precise nature of this influence is obscure and will remain so until more is known about the effects separately produced by each of the several factors that go to make up what is called climate. The prevalence of intense and varied colors among tropical insects is doubtless somewhat exaggerated, for the reason that the highly colored species naturally attract the eye to the ex- clusion of the less conspicuous forms. Indeed, Wallace assures us that, although tropical insects present some of the most gorgeous colors in the whole realm of nature, there are thousands of tropical species that are as dull colored as any of the temperate regions. Carabidz, in fact, attain their greatest brilliancy in the temperate zone, according to Wal- lace, though butterflies certainly show a larger proportion of vivid and varied colors in the tropics. Mayer finds, in the widely distributed genus Papilio, that 200 South American species display but 36 colors, while 22 North American species show 17. While the number of species in South America is nine times as great as in North America, the number of colors displayed is only a little more than twice as great; hence Mayer concludes that the richer display of colors in the tropics may be due to the far greater number of species, which gives a better opportunity for color sports to arise; and not to any direct influence of the climate. Furthermore, the number of COLOR AND COLORATION 201 broods which occur in a year is much greater in the tropics than in the temperate zones, so that the tropical species must possess a correspondingly greater opportunity to vary. Albinism and Melanism.—These interesting phenomena, widespread among the higher animals, are little understood, but appear to be due chiefly to temperature. Albinism is exceptional whiteness or paleness of coloration, and is due usually to lack or deficiency of pigment, but in some instances (Pieridz) to the presence of a white pigment. The common yellow butterfly, Colias philodice, and its rela- tives, are frequently albinic. Indeed, as Scudder observes, albinism among butterflies in America appears to be confined toramicw Pieridze, and’ io be restricted to the female: sex ;1t is more common in subarctic and subalpine regions than in lower latitudes and altitudes, and only in the former places does it include all the females. At low altitudes, instead of appear- ing early in the year as might be expected, the albinic forms appear during the warmer months. In Europe there are many albinic species of butterflies, and they are by no means confined to the family Pieride. Melanism is unusual blackness or darkness of coloration. As to how it is produced little is known, though warmth is probably the most potent influence, and some attribute it to moisture, as was mentioned. Pictet obtained partial melan- ism in Vanessa urtice and V. polychloros by subjecting the larvee to moisture. In warm latitudes, some females of our Papilio glaucus are blackish brown with black markings, instead of being, as usual, yellow with black markings. In the South, some males of the spring brood of Cyaniris pseudargiolus are partly or wholly brown instead of blue. Seasonal Coloration.—When butterflies have more than one brood in a year, the broods usually differ in aspect, some- times so much that their specific identity is revealed only by rearing one brood from another. The same species may exist under two or more distinct forms during the same sea- 202 ENTOMOLOGY son—in other words, may be seasonally dimorphic, trimorphic or polymorphic. : Thus Polygonia interrogations has two forms, fabricii and umbrosa, which differ not only in coloration, but even in the form of the wings and the genitalia. In New England fabricii hibernates and produces wmbrosa, as a rule, while wmbrosa usually yields fabricii. The little blue butterfly, Cyaniris pseudargiolus (Fig. 231), is polymorphic to a remarkable degree. In the high latitudes of Canada, a single brood (lucia) occurs. About Boston, the same spring brood appears, but under two forms: an earlier variety (lucia), which is small, with large black markings Cyaniris pseudargiolus; A, form lucia; B, violacea ; C, pseudargiolus proper. Natural size. beneath; and a later variety (violacea), which is typically larger, with smaller black spots, though it varies into the form lucia. Finally, in summer, a third form (pseudargiolus proper) appears, as the product of Jucia or else the joint prod- uct of lucia and violacea, and this is still larger, but the black spots are now faint. In the warm South, the spring form is violacea, but while some of the males are blue, others are melanic, as just mentioned—a dimorphic condition which does not occur in the North. Violacea then produces pseudargi- olus, in which, however, all the males are blue. Iphiclides ajax (Fig. 232) is another polymorphic butterfly whose life history is complex. The three principal varieties of this species, known respectively as marcellus, telamonides and ajax, differ not only in coloration, but also in size and form; marcellus appears first, in spring; telamonides appears COLOR AND COLORATION 203 a little later (though before marcellus has disappeared) ; and ajax is the summer form; as the season advances the varieties become successively larger, with longer tails to the hind wings. tes 232: Iphiclides ajax, form telamonides, on flower of button bush. Reduced. Now Edwards submitted chrysalides of the summer form ajax to cold and thereby obtained, in the same summer, butter- flies with the form of ajax but the markings of the spring Fic. 233. Phyciodes tharos; A, spring form, marcia; B, summer form, morpheus; under sur- faces. Natural size. form telamonides. Some of the chrysalides, however, lasted over until the next spring and then gave telamonides. 204 ENTOMOLOGY In Phyciodes tharos (Fig. 233) the spring and summer broods, termed respectively marcia and morpheus, were at first regarded as distinct species. In marcia the hind wings are heavily and diffusely marked beneath with strongly contrast- ing colors, while in morpheus they are plain and but faintly marked. Edwards placed upon ice eighteen chrysalides that normally would have produced morpheus; but instead of this, the fifteen imagines that emerged were all of the spring form marcia and were smaller than usual. Pupz derived from eges of marcia gave, after artificial cooling, not morpheus, but marcia again. The evident conclusion is that the distinc- tive coloration of the spring variety is brought about by low temperature. In Labrador, only one brood occurs—marcia; in New York, the species is digoneutic (two-brooded) and in West Virginia polygoneutic (several-brooded). Extensive temperature experiments upon seasonal dimor- phism in Lepidoptera have been conducted in Europe by some of the most competent biologists. Weismann found that pupze of the summer form of Pieris napi, if placed on ice, disclosed the darker winter form, usually in the same season, though sometimes not until the next spring. It was found impossible, however, to change the winter variety into the summer one by the application of heat. Similar results have attended the important and much-discussed experiments of Dorfmeister, Weismann and others upon Vanessa levana-prorsa and other species, from which it has been inferred by Weismann that the winter form is the primary, older, and more stable of the two forms, and the summer form a secondary, newer, and less stable variety; since the latter form only, as a rule, responds much to thermal influences. Weismann argues that, in addition to the direct effect of temperature, alternative inheritance also plays an important part in the production of seasonal varieties. He tries to show, moreover, that each seasonal variety is col- ored in adaptation to its particular environment and that this adaptation may have been brought about by natural selection— though he does not succeed in this respect. COLOR AND COLORATION 205 In several instances, local varieties have been artificially pro- duced as results of temperature control. Thus Standfuss produced in Germany, by the application of cold, individuals of Vanessa urtice which were indistinguishable from the northern variety polaris; and from pup of Vanessa cardui, by warmth, a very pale form like that found in the tropics; and, by cold, a dark variety similar to one found in Lapland. These investigators and others, notably Merrifield and Fischer, have accumulated a considerable mass of experimen- tal evidence, the interpretation of which is in many respects difficult, involving as it does, not merely the direct effect of temperature upon the organism, but also deep questions of heredity, including reversion, individual variation, and the in- heritance of acquired characters. The seasonal increase in size that is noticeable, as in C. pseudargiolus and I. ajax, is doubtless an expression of in- creasing metabolism due to increasing temperature. Warmth, as is well known, stimulates growth, and cold has a dwarfing effect. While this is true as a rule, there are some apparent exceptions, however. Thus Standfuss found that some cater- pillars were so much stimulated by unusual warmth that they pupated before they were sufficiently fed, and gave, therefore, undersized imagines. A moderate degree of warmth, how- ever, undoubtedly hastens growth. Sexual Coloration.—The sexes are often distinguished by colorational as well as structural differences. Colorational antigeny (this word signifying secondary sexual differences of whatever sort) is most prevalent among butterflies, in which it is the extreme phase of that differentiation of orna- mentation for which Lepidoptera are unrivaled. The male of Pieris protodice (Fig. 234) has a few brown spots on the front wings; the female is checkered with brown on both wings. In Colias philodice (Fig. 235) and C. eury- theme the marginal black band of the front wings is sharp and uninterrupted in the male, but diffuse and interrupted by yellow spots in the female. In the genus Papilio the sexes 206 ENTOMOLOGY Fig. 234. Pieris protodice; male (on the left) and female (on the right). Natural size. are often distinguished by colorational differences and in Hes- periidz the males often have an oblique black dash across the middle of each front wing. Callosamia promethea (Fig. 236), the gypsy moth and many other Lepidoptera exhibit colorational antigeny. In not a few Sestidz the sexes differ ; greatly in coloration. Thus in the Pig 235: male of the peach tree borer (San- ninoidea exitiosa) all the wings are colorless and transparent; while in the female the front wings are vio- let and opaque and the fourth ab- dominal segment is orange above. The same sex may present two types of coloration, as do males of Cyanuris pseudargiolus and females of Papilio glaucus, already men- tioned. Papilio merope, of South Africa, is remarkable in having three Colias philodice; right fore females ( Frontispiece, Figs. 5; 7> 9; wing of male (above) and of 7) which are entirely different in female (below). Natural size. ‘ cs coloration from one another and from the male. There is no longer any doubt, it may be added, as to the specific identity of these forms. Next to Lepidoptera, Odonata most frequently show col- orational antigeny. The male of Calopteryx maculata is vel- COLOR AND COLORATION 207 vety black; the female smoky, with a white pterostigmatal spot. Among Coleoptera, the male of Hoplia trifasciata is grayish and the female reddish brown; a few more examples might be given, though sexual differences in coloration are Callosamia promethea; A, male, clinging to cocoon; B, female. Reduced. comparatively rare among beetles. Of Hymenoptera, some of the Tenthredinidz exhibit colorational antigeny. Among tropical butterflies there are not a few instances in which the special coloration of the female is adaptive—har- monizing with the surroundings or else imitating with remark- able precision the coloration of another species which is known 208 ENTOMOLOGY to be immune from the attacks of birds—as described beyond. In this way, as Wallace suggests, the egg-laden females may escape destruction, as they sluggishly seek the proper plants upon which to lay their eggs. Here would be a fair field for the operation of natural selection. In most insects, however, sexual differences in coloration are apparently of no protective value and are usually so trivial and variable as.probably to be of no use for recognition pur- poses. The usual statement that these differences facilitate sexual recognition 1s a pure assumption, in the case of insects, and one that is inadequate in spite of its plausibility, for (1) it is extremely improbable from our present knowledge of insect vision that insects are able to perceive colors except in the broadest way, namely, as masses; (2) the great majority of insect species show no sexual differences in coloration; (3) when colorational antigeny is present it is probably unneces- sary, to say the least, for sexual recognition. Thus, notwith- standing the marked dissimilarity of coloration in the two sexes of C. promethea, the males, guided by an odor, seek out their mates even when the wings of the female have been am- putated and male wings glued in their place, as Mayer found. Hence, when useless, colorational antigeny cannot have been developed by natural selection and may be due simply to the extended action of the same forces that have produced variety of coloration in general. Origin of Color Patterns.—Tower, who has written an important work on the colors and color patterns of Coleop- tera, finds that each of the black spots on the pronotum of the Colorado potato beetle (Fig. 237) “is developed in connection with a muscle, and marks the point of attachment of its fibers to the cuticula.” Thus the color pattern, in its origin, is not neces- sarily useful. This point is so important that we quote Tow- er’s conclusions in full. ‘‘ The most important and widely disseminated of insect colors are those of the cuticula these colors develop as the cuticula hardens, and appear first, as a rule, upon sclerites to which muscles are attached. ~ In COLOR AND COLORATION 209 one of the earlier sections of this paper I showed that the pig- ment develops from before backward and, approximately, by segments, excepting that it may appear upon the head and most posterior segments simultaneously. “In ontogeny color appears first, as a rule, over the muscles which become active first, or upon certain sclerites of the body. These are usually the head muscles, although exceptions are not infrequent. It should be remembered that as the color appears the cuticula hardens, and, considering that muscles must have fixed ends for their action, it seems that there is a definite relation between the development of color, the hard- ening of the cuticula, and the beginning of muscular activity ; the last being dependent upon the second, and, incidentally, accompanied by the first. As muscular activity spreads over the animal the cuticula hardens and color appears, so that color is nearly, if not wholly, segmentally developed. “ The relation which exists between cuticular color and the stiffening of the cuticula is thus a physiological one, the cutic- ula not being able to harden without becoming yellow or brown. What bearing has this upon the origin of color pat- terns? In the lower forms of tracheates, such as the Myria- pods, colors appear as segmental repetitions of spots or pig- mented areas which mark either important sclerites or muscle attachments. On the abdomens of insects, where segmenta- tion is best observed, color appears as well-defined, segmen- tally arranged spots, but on the thorax segmentation is ob- scured and lost upon the head. Of what importance, then, is pigmentation? And how did it arise? If the ontogenetic stages offer any basis for phylogenetic generalization, we may conclude that cuticula color originated in connection with the hardening of the integument of the ancestral tracheates as necessary to the muscular activity of terrestrial life. The primitive colors were yellows, browns and blacks, correspond- ing well with the surroundings in which the first terrestrial insects are supposed to have lived. The color pattern was a segmental one, showing repetition of the same spots upon suc- cessive segments, as upon the abdomen of Coleoptera. 15 210 EN TOMOLOGY “So firmly have these characters become ingrained in the tracheate series, and so important is this relation of the hard- ening of the cuticula to the musculature and to the formation of body sclerites, that even the most specialized forms show this primitive system of coloration; and, although there may be spots and markings which have no connection with it, still the chief color areas are thus closely associated.” Development of Color Patterns.—Although the causes of coloration are, for the most part, obscure, it is possible, never- theless, to point out certain paths along which coloration ap- pears to have developed. These paths have been determined by the comparison of color patterns in kindred groups of 1n- sects and the study of colorational variations in adults of the same species. The development of coloration in the individ- - ual, however, has as yet received but little attention—excepting the excellent studies of Mayer and of Tower. Butterflies, moths and beetles have naturally been preferred by most stu- dents of the subject. The most primitive colors among moths are uniform dull yellows, browns and drabs—the same colors that the pupal blood assumes when it is dried in the air. These simple col- ors prevail on the hind wings of most moths and on the less exposed parts of the wings of highly colored butterflies. The hind wings of moths are, as a rule, more primitively colored than the front ones because, as Scudder says, “all differen- tiation in coloring has been greatly retarded by their almost universal concealment by day beneath the overlapping front wings.” Exceptions to this statement are found in Geomet- ride and such other moths as rest with all the wings spread. “Tn such hind wings we find that the simplest departure from uniformity consists in a deepening of the tint next the outer mar- gin of the wing; next we have an intensification of the deeper tint along a line parallel to the margin; it is but a step from this condition to a distinct line or band of dark color parallel to the margin. Or the marginal shade may, in a similar way, break up into two or more transverse and parallel submarginal COLOR AND COLORATION 211 lines, a very common style of ornamentation, especially in moths. Or, again, starting with the submarginal shade, this may send shoots or tongues of dark color a short distance toward the base, giving a serrate inner border to the marginal shade; when now this breaks up into one, two, or more lines or narrow stripes, these stripes become zigzag, or the inner a very ones may be zigzag, while the outer ones are plain common phenomenon. “A basis such as this is sufficient to account for all the modi- fications of simple transverse markings which adorn the wings of Lepidoptera.” Briefly, one or more bands may break up into spots or bars, the breaks occurring either between the veins or, more com- monly, at the veins; and in the latter event, short bars or more or less quadrate or rounded spots arise in the interspaces. From simple round spots there may develop, as Darwin and others have shown, many-colored eye-like spots, or ocelli. Mayer gives the following laws of color pattern: “ (a) Any spot found upon the wing of a butterfly or moth tends to be bilaterally symmetrical, both as regards form and color; and the axis of symmetry is a line passing through the center of the interspace in which the spot is found, parallel to the longi- tudinal nervures. (b) Spots tend to appear not in one inter- space only, but in homologous places in a row of adjacent interspaces. (c) Bands of color are often made by the fusion of a row of adjacent spots, and, conversely, chains of spots are often formed by the breaking up of bands. (d) When in process of disappearance, bands of color usually shrink away at one end. (e) The ends of a series of spots are more vari- able than the middle. (f) The position of spots situated near the outer edges of the wing is largely controlled by the wing- folds or creases.” These results have been arrived at chiefly by the study of the variations presented by color patterns. Variation in Coloration.—It is safe to say that no two insects are colored exactly alike. Some species, however, are HIG 237. a & © a3 z ~ ~ dD — ie nD 15 € Colorational variations of the pronotum of the Colorado potato beetle, Leptinotarsa decemlineata. (212) Fic. 238. 6 5 4 13 14 15 18 Elytral color patterns of species of Cicindela. 1-8 illustrate reduction of dark area; 9-14, extension of dark area; 15, 16, formation of longitudinal vitta; 17, 18, linear extension of markings. 1, C. vulgaris; 2, generosa; 3, generosa; 4, pamphila; 5, lim- bata; 6, togata; 7, gratiosa; 8, canosa; 9, tenuisignata; 10, marginipennis; 11, hentzii; I2, sexguttata; 13, hemorrhagica; 14, splendida; 15, imperfecta; 16, lemniscata; 17, gabbu; 18, saulcyi.imAfter Horn, from Entomological News. (213) 214 EN TOMOLOGY far more variable than others. Catocala ila, for example, occurs under more than fifty varieties, each of which might be given a distinctive name, were it not for the fact that these varieties run into one another. One may examine hundreds of potato beetles (L. decemlineata) without finding any two that have precisely the same pattern on the pronotum. The range of this variation in this species is partially indicated in Fig. 237, and that of Cicindela in Fig. 238. Individuals of Cicindela vary in pattern in a few definite directions, and the patterns that characterize the various spe- cies appear to be fixations of individual variations. In the words of Dr. Horn: “ (1) The type of marking is the same in all our species. (2) Assuming a well-marked species (vul- igaris, Fig. 238, 1) as a central type, the markings of other species vary from that type, (a) by a progressive spreading of the white, (b) by a gradual thinning or absorption of the white, (c) by a fragmentation of the markings, (d) by linear supplementary extension. (3) Many species are practically invariable (7. ¢., the individual variations are small in amount as compared with those in other species). These fall into two series: (a) those of the normal type, as vulgaris, lurticollis and tenwisignata; (b) those in which some modification of the type has become permanent, probably through isolation, as marginipenms, togata and lemmiscata. (4) Those species which vary do so in one direction only.” New types of pat- tern, of specific value, appear to have arisen by the isolation and perpetuation of individual variations. Variations in general fall into two classes: continuous (1n- dividual variations) and discontinuous (sports). The former are always present, are slight in extent and intergrade with one another; they are distributed symmetrically about a mean condition. The latter are occasional, of considerable extent and sharply separated from the normal condition. Replacements. by another are familiar to all collectors. The red of Vanessa atalanta and Coccinellidee may be replaced by yellow. These Examples of the replacement of one color COLOR AND COLORATION 215 two colors in many butterflies and beetles are due to pigments that are closely related to each other chemically. Thus in the chrysomelid Melasoma lapponica the beetle at emergence is pale but soon becomes yellow with black markings, and after several hours, under the influence of sunlight, the yellow changes to red; the change may be prevented, however, by keep- ing the beetle in the dark. After death, the red fades back through orange to yellow, especially as the result of exposure to sunlight. Yellow in place of red, then, may be attributed to an arrested development of pigment in the living insect and to a process of reduction in the dead insect, metabolism having ceased. Yellow and green are similarly related. The stripes of Pecilocapsus lineatus are yellow before they become green, and after death fade back to yellow. As the green pigment in most, if not all, phytophagous insects is chlorophyll, these color changes are probably similar to those that occur in leaves. Leaves grown in darkness are yellow, from the presence of etio- lin, and do not turn green until they are exposed to sunlight (or electric light), without which chlorophyll does not develop; and as metabolism ceases, chlorophyll disintegrates, as in autumn, leaving its yellow constituent, xanthophyll, which is very likely the same substance as etiolin. Cicindela sexguttata and Calosoma scrutator are often blue in place of green. Here, however, these colors are structural, and their variations are to be attributed to slight differences in the spacing of the surface elevations or depressions. Green grasshoppers occasionally become pink toward the close of summer. No explanation has been offered for this phenomenon, though it may be remarked that when grasshop- pers are killed in hot water the normal green pigment turns to pink. These changes of color are apparently of no use to the insect, being merely incidental effects of light, temperature or other inorganic influences. CEASE Toya ADAPTIVE COLORATION Protective Resemblance.—F very naturalist knows of many animals that tend to escape detection by resembling their surroundings. This phenomenon of protective resemblance is richly exemplified by insects, among which one of the most remarkable cases is furnished by the Kallima butterflies, espe- cially K. inachis of India and K. parakieta of the Malay Archi- pelago. The former species (Fig. 239) is conspicuous when Fic. 230. Kallima inachis; A, upper surface; B, with wings closed, showing resemblance to a leaf. xX 4. on the wing; its bright colors, however, are confined to the upper surfaces of the wings, and when these are folded to- gether, as in repose, the insect resembles to perfection one of the dead leaves among which it is accustomed to hide. The form, size and color of the leaf are accurately reproduced, the petiole being simulated by the tails of the wings. Two paral- lel shades, one light and one dark, represent, respectively, 216 ADAPTIVE COLORATION 217 the illuminated and the shaded side of a mid-rib, and the side- veins as well are imitated; there are even small scattered black spots resembling those made on the leaf by a species of fungus. Furthermore, the butterfly habitually rests, not among green leaves, where it would be conspicuous, but among leaves with which it har- monizes in coloration. Fic. 240. Notwithstanding a recent discussion as to whether it usually rests in pre- cisely the same position as a leaf, this insect cer- tainly deceives experi- enced entomologists and presumably eludes birds and other enemies by means of its deceptive coloration. Some of the tropical Phasmide counterfeit sticks, green leaves, or dead leaves with minute accuracy. Our common phasmids, Diapheromera femorata and veliei (Fig. 240), are well known as “stick insects’’; indeed, it is not necessary to go beyond the temperate zone if Diapheromera velieit, on a twig. Natural size. to find plenty of examples of protective resemblance. Geometrid caterpillars imitate twigs, holding the body stiffly from a branch and frequently reprodu- cing the form and coloration of a twig with striking exactitude ; and the moths of the same family are often colored like the bark against which they spread their wings. [ven more per- fectly do the Catocala moths resemble the bark upon which Bits) ENTOMOLOGY they rest (Fig. 241), with their conspicuous and usually showy hind wings concealed under the protectively colored front wings. The caterpillars of Basilarchia archippus and Pa- pilio thoas, as well as other larve and not a few moths, resemble closely the excrements of birds. Numerous grass- Ringe s2Aie Catocala lacrymosa; A, upper surface; B, with wings closed, and resting on bark. Reduced. eating caterpillars are striped with green, as is also a sphingid species (Ellema harris) that lives among pine needles. The large green sphinx caterpillars perhaps owe their inconspicu- ousness partly to their oblique lateral stripes, which cut a mass of green into smaller areas. The caterpillar of Sclgura ipomee (Fig. 242), which is green with brown patches, rests ADAPTIVE COLORATION 219 for hours along the eaten or torn edge of a basswood leaf, in which position it bears an extremely deceptive resemblance to the partially dead border of a leaf. The weevils that drop to the ground and remain immovable are often indistinguishable Pies 242) Caterpillar of Schizura ipom@e clinging to a torn leaf. Natural size. to the collector on account of their likeness to bits of soil or little pebbles. Everyone has noticed the extent to which some of the grasshoppers resemble the soil in color; Trimerotropis maritima is practically invisible against the gray sand of the seashore or other places to which it restricts itself; and Dis- sosteira carolina, which varies greatly in color, ranging from ashy gray to yellowish or to reddish brown, is commonly found on soil of its own color. Adventitious Resemblance.—If, instead of hastily ascrib- ing all cases apparently of protective resemblance to the action of natural selection, one inquires into the structural basis of the resemblance in each instance, it is found that some cases can be explained, without the aid of natural selection, as being 220 EN TOMOLOGY direct effects of food, light or other primary factors. Such cases, then, are in a sense accidental. For example, many inconspic- uous green insects are green merely because chlorophyll from the food-plant tinges the blood and shows through the skin. If it be argued that natural selection has brought about a thin and transparent skin, it may be replied that the skin of a green caterpillar is by no means exceptional in thinness or trans- parency. Moreover, many leaf-mining caterpillars are green, simply because their food is green; for, living as they do within the tissues of leaves, and surrounded by chlorophyll, their own green color is of no advantage, but is merely incidental. Again, in the “ protectively ’ colored chrysalides experi- mented upon by Poulton, their color was directly influenced by the prevailing color of the light that surrounded the larva during the last few days before pupation. Of course, it is conceivable that natural selection may have preserved such in- dividuals as were most responsive to the stimulus of the sur- rounding light; nevertheless the fact remains that these resem- blances do not demand such an explanation, which is, in other words, superfluous. Indeed, a great many of the assumed examples of “ protec- tive resemblance”’ are very far-fetched. On the other hand, when the resemblance is as specific and minutely detailed as it is in the Kallima butterflies—where, moreover, special instincts are involved—the phenomenon can scarcely be due to chance; the direct and uncombined action of such factors as food or light is no longer sufficient to explain the facts—although these and other factors are undoubtedly important in a primary, or fundamental, way. Here natural selection becomes useful, as enabling us to understand how original variations of structure and instinct in favorable directions may have been preserved and accumulated until an extraordinary degree of adaptation has been attained. Value of Protective Resemblance.—The popular opinion as to the efficiency of protective resemblances is undoubtedly an exaggerated one, owing mainly to the false assumption that ADAPTIVE COLORATION 221 the senses of the lower animals are co-extensive in range with our own. As a matter of fact, birds detect insects with a facility far superior to that of man, and destroy them by the wholesale, in spite of protective coloration. Thus, as Judd has ascertained, no less than three hundred species of birds feed upon protectively colored grasshoppers, which they destroy in immense numbers, and more than twenty species prey upon the twig-like geometrid larve; while the weevils that look like particles of soil, and the green-striped caterpillars that assimilate with the surrounding foliage are constantly to be found in the stomachs of birds. After all, however, protective resemblance may be regarded as advantageous upon the whole, even if it is ineffectual in thousands of instances. An adaptation may be successful even if it does fall short of perfection; and it should be borne in mind that the evolution of protective resemblances among insects has probably been accompanied on the part of birds by an increasing ability to discriminate these insects from their surroundings. Warning Coloration.—In strong contrast to the protec- tively colored species, there are many insects which are so vividly colored as to be extremely conspicuous amid their nat- ural surroundings. Such are many Hemiptera (Lygeus, Murgantia), Coleoptera (Necrophorus, Lampyridz, Coccinel- lide, Chrysomelide), Hymenoptera (Mutillide, Vespide), and numerous caterpillars and butterflies. Conspicuous col- ors, being frequently—though not always—associated with qualities that render their possessors unpalatable or offensive to birds or other enemies, are advantageous if, by insuring ready recognition, they exempt their owners from attack. Efficiency of Warning Colors.—Owing to much disagree- ment as to the actual value of “ warning” colors, several in- vestigators have made many observations and experiments upon the subject. Tests made by offering various conspicu- ous insects to birds, lizards, frogs, monkeys and other insec- tivorous animals have given diverse results, according to cir- i) NO NO ENTOMOLOGY cumstances. Thus, one gaudy caterpillar is refused by a cer- tain bird, at once, or else after being tasted, but another and equally showy caterpillar is eaten without hesitation. Or, an insect at first rejected may at length be accepted under stress of hunger; or a warningly colored form disregarded by some animals is accepted by others. Moreover, some of the experi- ments with captive insectivorous animals are open to objection on the score of artificiality. Nevertheless, from the data now accumulated, there emerge some conclusions of definite value. Frank Finn, whose con- clusions are quoted beyond, has found in India that the con- spicuous colors of some butterflies (Danainz, Acrea viole, Delias eucharis, Papilio aristoloch@) are probably effective as “warning” colors. Marshall found in South Africa that: mantids, which would devour most kinds of butterflies, includ- ing warningly colored species, refused Acrea, which appeared to be not only distasteful but even unwholesome; Acrea is eaten, however, by the predaceous Asilidz, which feed indis- criminately upon insects—for example, beetles, dragon flies and even stinging Hymenoptera. The masterly studies of Mar- shall and Poulton strongly support the general theory of warn- ing coloration. In this country, much important evidence upon the subject has been obtained by Dr. Judd from an extensive examination of the stomach-contents of birds, supplemented by experiments and field observations. Judd says that Murgantia histrionica and other large showy bugs are usually avoided by birds; that the showy, ill-flavored Coccinellidze, and Chrysomelidz such as the elm leaf beetle, Diabrotica, and Leptinotarsa (Dory- phora), possess comparative immunity from birds; and that Macrodactylus, Chauliognathus and Cyllene are highly exempt from attack. Such cases, he adds, are comparatively few among’ insects, however, and in general, warning colors are effective against some enemies but ineffective against others. Generally speaking, hairs, stings and other protective de- vices are accompanied by conspicuous colors—though there ADAPTIVE COLORATION 223 are many exceptions to this rule. These warning colors, how- ever, fail to accomplish their supposed purpose in the follow- ing instances, given by Judd. Taking insects that are thought to be protected by an offensive odor or a disagreeable taste: Heteroptera in general are eaten by all insectivorous birds, the squash bug by hawks and the pentatomids by many birds; among Carabidz with their irritating fluids, Harpalus caligi- nosus and pennsylvanicus are food for the crow, catbird, robin and six others; Carabus and Calosoma are relished by crows and blackbirds; Silphidze are taken by the crow, loggerhead shrike and kingbird; and Leptinotarsa decemlineata is eaten by at least six kinds of birds: wood thrush, rose-breasted gros- beak, quail, crow, cuckoo and catbird. Of hairy and spiny cat- erpillars, Arctiidz are eaten by the robin, bluebird, catbird, cuckoo and others; the larve of the gypsy moth are food for the blue-jay, robin, chickadee, Baltimore oriole and many others [thirty-one birds, in Massachusetts]; and the spiny caterpillars of Vanessa antiopa are taken by cuckoos and ori- oles. Of stinging Hymenoptera, bumble bees are eaten by the bluebird, blue-jay and two flycatchers; the honey bee, by the wood pewee, phcebe, olive-sided flycatcher and kingbird; Andrena by many birds, and Vespa and Polistes by the red- bellied woodpecker, kingbird, and yellow-bellied flycatcher. These facts by no means invalidate the general theory, but they do show that “ disagreeable” qualities and their associ- ated color signals are of little or no avail against some enemies. The weight of evidence favors the theory of warning colora- tion in a qualified form. While conspicuous colors do not always exempt their owners from destruction, they frequently do so, by advertising disagreeable attributes of one sort or another. The evolution of warning coloration is explained by natural selection; in fact, we have no other theory to account for it. The colors themselves, however, must have been present before natural selection could begin to operate; their origin is a ques- tion quite distinct from that of their subsequent preservation. to i) ne ENTOMOLOGY Protective Mimicry.—This interesting and highly involved phenomenon is a special form of protective resemblance in which one species imitates the appearance of another and Fic. 243. A, Anosia plexippus, the ‘‘ model”; B, Basilarchia archippus, the “ mimic.” Natural size. better protected species, thereby sharing its immunity from destruction. Though it attains its highest development in the tropics, mimicry is well illustrated in temperate regions. A familiar example is furnished by Basilarchia archippus (Fig. 243, B), which departs widely from the prevailing dark colora- tion of its genus to imitate the milkweed butterfly, dnosia ADAPTIVE COLORATION 2 iS) UL ‘ plexippus. The latter species, or “ model,’ appears to be un- molested by: birds, and the former species, or “ mimic,” 1s thought to secure the same exemption from attack by being mistaken for its unpalatable model. The common drone-fly, Eristalis tenax (Fig. 244, B) mimics a honey bee in form, size, Fic. 244. Protective mimicry. A, drone bee, Apis mellifera; B, drone fly, Eristalis tenax. Natural size. coloration and the manner in which it*buzzes about flowers, in company with its model; it does not deceive the kingbird and the flicker, however. Some Asilidz are remarkably like bumble bees in superficial appearance and certain Syrphus flies mimic wasps with more or less success. The beetle Casnonia bears a remarkable resemblance to the ants with which it lives. The classic cases are those of the Amazonian Heliconiide and Pieridz, in which mimicry was first detected by Bates. The Heliconiide (Frontispiece, Fig. 1) are abundant, vividly colored and eminently free from the attacks of birds and other enemies of butterflies, on account of their disagreeable odor and taste. Some of the Pieridze—a family fundamentally dif- ferent from Heliconiide—imitate (Frontispiece, Fig. 2) the protected Heliconiidze so successfully, in coloration, form and flight, that while other Pieridz are preyed upon by many foes, the mimicking species tend to escape attack. The family Heliconiide, referred to by Bates, comprised what are now known as the subfamilies Helicontinz, Itho- miinz and Danainz; similarly, Pieridze and Papilionidz are 16 226 ENTOMOLOGY now often termed respectively Pierinz and Papilionine. Ithomiinz are mimicked also by Papilioninee and by moths of the families Castniidze and Pericopide. The discoveries of Bates in tropical South America were paralleled and supported by those of Wallace in India and the Malay Archipelago (where Danainz are the chief “ medels”’), and of Trimen in South Africa (where Acreinz and Danainz serve as models). Trimen discovered a most remarkable case, in which three species of Danainz are mimicked, each by a distinct variety of the female of Papilio merope (Frontispiece, Figs. 5-11). So much for that kind of mimicry—but how is the following kind to be explained? The Ithominze of the Amazon valley have the same form and coloration as the Helicontinz ( Frontis- piece, Figs. 1, 4), but the Ithomunz themselves are already highly protected. The answer is that this resemblance is of advantage to both groups, as it minimizes their destruction by birds—these having to learn but one set of warning signals instead of two. This is the essence of Muller’s famous expla- nation, which will presently be stated with more precision. There are two kinds of mimicry, then: (1) the kind described by Bates, in which an edible species obtains security by coun- terfeiting the appearance of an inedible species; (2) that ob- served by Bates and interpreted by Muller, in which both species are inedible. These two kinds are known respectively as Batesian and Mullerian mimicry, though some writers prefer to limit the term mimicry to the Batesian type. ’ Wallace’s Rules.—The chief conditions under which mimi- cry occurs have been stated by Wallace as follows: “1, That the imitative species occur in the same area and occupy the very same station as the imitated. “2. That the imitators are always the more defenceless. “3. That the imitators are always less numerous in indi- viduals. “4. That the imitators differ from the bulk of their allies. CG 5. That the imitation, however minute, is external and ADAPTIVE COLORATION 227 visible only, never extending to internal characters or to such as do not affect the external appearance.” These rules relate chiefly to the Batesian form of mimicry and need to be altered to apply to the Mullerian kind. The first criterion given by Wallace is evidently an essential one and it is sustained by the facts. It is also true that mimic and model occur usually at the same time of year; Marshall found many new instances of this in South Africa. In some cases of mimicry, strange to say, the precise model is unknown. Thus some Nymphalide diverge from their relatives to mimic the Eupleeine, though no particular model has been found. In such instances, as Scudder suggests, the prototype may exist without having been found; may have become extinct; or the species may have arrived at a general resemblance to another group without having as yet acquired a likeness to any particular species of the group, the general likeness mean- while being profitable. The second condition named by Wallace is correct for Batesian but not for Mullerian mimicry. The fulfilment of the third condition is requisite for the success of Batesian mimicry. Bates noted that none of the pierid mimics were so abundant as their heliconiid models. If they were, their protection would be less; and should the mimic exceed its model in numbers, the former would be more subject to attack than the latter. Sometimes, indeed, as Muller found, the mimic actually is more common than the model; in which event, the consequent extra destruction of the mimic would—at least theoretically—treduce its numbers back to the point of protection. In Mullerian mimicry, however, the inevitable variation in abundance of two or more converging and protected species is far less disastrous; though when two species, equally distaste- ful, are involved, the rarer of the two has the advantage, as Fritz Muller has shown. His lucid explanation is essentially as follows: Suppose that the birds of a region have to destroy 1,200 228 ENTOMOLOGY butterflies of a distasteful species before it becomes recognized as such, and that there exist in this region 2,000 individuals of species A and 10,000 of species B; then, if they are different in appearance, each will lose 1,200 individuals, but if they are deceptively alike, this loss will be divided among them in pro- portion to their numbers, and 4 will lose 200 and B 1,000. A accordingly saves 1,000, or 50 per cent. of the total number _of individuals of the species, and B saves only 200, or 2 per cent. Thus, while the relative numbers of the two species are as I to 5, the relative advantage from their resemblance is as Ze tO) Ll: If two or more distasteful species are equally numerous, their resemblance to one another brings nearly equal advan- tages. In cases of this kind—and many are known—it is. sometimes impossible to distinguish between model and mimic, as all the participants seem to have converged toward a com- mon protective appearance, through an interchange of features —the “reciprocal mimicry ” of Dr. Dixey. From this explanation, the superior value of Mullerian as compared with Batesian mimicry is evident. The fourth condition—that the imitators differ from the bulk of their allies—holds true to such a degree that even the two sexes of the same species may differ extremely in colora- tion, owing to the fact that the female has assumed the like- ness of some other and protected species. The female of Papilio merope, indeed, occurs (as was just mentioned) under three varieties, which mimic respectively three entirely dissim- ilar species of Danainz, and none of the females are any- thing like their male in coloration (Frontispiece, Figs. 5-11). The specific identity of these four South African varieties of merope has been established by Trimen, Marshall and other investigators. The generally accepted explanation for these remarkable but numerous cases in which the female alone 1s mimetic, is that the female, burdened with eggs and consequently sluggish in flight and much exposed to attack, is benefited by imitating ADAPTIVE COLORATION 229 a species which is immune; while the male has had no such incentive—so to speak—to become mimetic. Of course, there has been no conscious evolution of mimicry. Wallace’s fifth stipulation is important, but should read this way: “ The imitation, however minute, is but external and visible wsually, and never extends to internal characters w/ich do not affect the external appearance.” For, as Poulton points out, the alertness of a beetle which mimics a wasp, implies appropriate changes in the nervous and muscular sys- tems. In its intent, however, Wallace’s rule holds good, and by disregarding it some writers strain the theory of mimicry beyond reasonable limits. Some have said, for example, that the resemblance between caddis flies and moths is mimicry; when the fact is that this resemblance is not merely superficial but is deep-seated; the entire organization of Trichoptera shows that they are closely related to Lepidoptera. ‘This like- ness expresses, then, not mimicry, but affinity and parallel development. The same objection applies to the assumed cases of mimicry within the limits of a single family, as be- tween two genera of Heliconiidze or between the chrysomelid genera Lema and Diabrotica. Vhe nearer two species are related to each other, the more probable it becomes that their similarity is due— not to mimicry—but to their common ancestry. FIG. 245. On the other hand, the resemblance frequently occurs between species of such ‘ : 5 A locustid, Myrme- Gitenent orders that it cannotcbe-attsib- copnana fallax, which Medio atnmity. (Ullustrations of this are “sembles a2 ent Twice = natural tength. From the mimicry of the honey bee by the Brunner von Wat- TENWYL. drone fly, and the many other instances in which stinging Hymenoptera are counterfeited by harmless flies or beetles. A locustid of the Soudan resembles an ant (Fig. 245), and the resemblance, by the way, is obtained in a most remarkable manner. Upon the stout body of this or- thopteron the abdomen of an ant is delineated in black, the rest 230 ENTOMOLOGY of the body being light in color and inconspicuous by contrast with the black. Indeed the various means by which a super- ficial resemblance is brought about between remotely related insects are often extraordinary. Irrespective of affinity, insects of diverse orders may con- verge in wholesale numbers toward a central protected form. The most complete examples of this have recently been brought to light by Marshall and Poulton, in their splendid work on the bionomics of South African insects, in which is given, for instance, a colored plate showing how closely six distasteful and dominant beetles of the genus Lycus are imitated by nearly forty species of other genera—a remarkable example of con- vergence involving no less than eighteen families and five or- ders, namely, Coleoptera, Hymenoptera, Hemiptera, Lepidop- tera and Diptera. Excepting a few unprotected, or Batesian, mimics (a fly and two or three beetles), this association is one between species that are already protected, by stings, bad tastes or other peculiarities. In other words, here is Muller- ian mimicry on an immense scale; and if Mullerian mimicry is profitable when only two species are concerned, what an enormous benefit it must be to each of forty participants! Strength of the Theory.—Evidently the theory of mimicry rests upon the assumption that the mimics, by virtue of their mimicry, are specially protected from insectivorous foes. Un- til the last few years, however, there was altogether too little positive evidence bearing upon the assumption itself, though this was supported by such scattered observations as were available. The oft-repeated assertion that this lack of evi- dence was due simply to inattention to the subject, has been proved to be true by the decisive results recently gained in the tropics by several competent investigators who have been able to give the subject the requisite amount of attention. From his observations and experiments in India, Frank Finn concludes : “1. That there is a general appetite for butterflies among insectivorous birds, even though they are rarely seen when wild to attack them. ADAPTIVE COLORATION 231 “2. That many, probably most species, dislike, if not in- tensely, at any rate in comparison with other butterflies, the warningly-colored Danainz, Acrea viole, Delias eucharis, and Papilio aristolochie; of these the last being the most distaste- ful, and the Danainz the least so. “ 2. That the mimics of these are at any rate relatively palatable, and that the mimicry is commonly effectual under natural conditions. | “4. That each bird has separately to acquire its experience, and well remembers what it has learned. * That therefore on the whole, the theory of Wallace and Bates is supported by the facts detailed in this and my former papers, so far as they deal with birds (and with the one mam- mal used). Professor Poulton’s suggestion that animals may be forced by hunger to eat unpalatable forms is also more than confirmed, as the unpalatable forms were commonly eaten without the stimulus of actual hunger—generally, also, | may add, without signs of dislike.” Though insects have many vertebrate and arthropod ene- mies, it is probable that the evolution of mimetic resemblance, implying warning coloration, has been brought about chiefly by insectivorous birds. Neglecting papers of minor importance, we may pass at once to the most important contribution upon this subject— the voluminous work of Marshall and Poulton upon mimicry and warning colors in South African insects. These investi- gators have found that birds are to be counted as the principal enemies of butterflies; that the Danainz and Acreinz, which are noted as models, are particularly immune from destruc- tion, while unprotected forms suffer; and that mimicking, though palatable species, share the freedom of their models. The same is true of beetles, of which Coccinellide, Mala- codermide (notably Lycus), Cantharidze and many Chryso- melidze serve as models for many other Coleoptera, being “conspicuous and constantly refused by insect-eaters.” In short, the splendid work of Marshall and Poulton tends to 232 ENTOMOLOGY place the theory of Batesian and Mullerian mimicry upon a substantial foundation of observational and experimental evidence. In regard to the important question—do birds avoid un- palatable insects instinctively or only as the result of experi- ence—the evidence is all one way. Several investigators, in- cluding Lloyd Morgan, have found that newly-hatched birds have no instinctive aversions as regards food, but test every- thing, and (except for some little parental guidance) are obliged to learn for themselves what is good to eat and what is not. This experimental evidence that the discrimination of food by birds is due solely to experience, was evidently highly necessary to place the theory of mimicry—especially the Mul- lerian theory—upon a sound basis. Though butterflies as a group are much subject to the at- tacks of birds in the tropics, there are very few recorded in- stances of this for our temperate region. It may then be asked, what advantage does the “ viceroy” (Fig. 243, B) gain by resembling the “ monarch,” in a region where all butter- flies are exempt from destruction by birds? In reply, it may be said that the premise of the argument is as yet little more than an assumption, because so little attention has been given to the relations between birds and butterflies in our own coun- try. Or,admitting the premise, it may be said that the resem- blance was advantageous once, if not now; and that in any event, the departure of arclippus from its congeners toward one of the Danainze—a famous group of “ models” in the tropics—is unintelligible except as an instance of mimicry. Granting that mimicry is upon the whole advantageous, it becomes important to learn just how far the advantage ex- tends; and we find that mimicry is not of universal effective- ness. Even the highly protected Heliconiinz and Danainz are food for some predaceous insects. In this country, as Judd has observed, the drone-fly (Eristalis tenax), which mimics the honey bee, is eaten by the kingbird and the phoebe; the kingbird, indeed, eats the honey bee itself, but is said to i) ADAPTIVE COLORATION pick out the drones; chickens also discriminate between drones and workers, eating the former and avoiding the latter. Bum- ble bees and wasps, imitated by many other insects, are them- selves eaten by the kingbird, catbird and several other birds, though it is not known whether the stingless males of these are singled out or not. Such facts as these do not discredit the general theory of mimicry but point out its limits. Evolution of Mimicry.—Natural selection gives an adequate explanation of the evolution of a mimetic pattern. Before accepting this explanation, however, we must inquire: (1) What were the first stages in the development of a mimetic pattern? (2) What evidence is there that every step in this development was vitally useful, as the theory demands that it should be? These pertinent questions have been answered by Darwin, Wallace, Muller, Dixey and several other authorities. The incipient mimic must have possessed, to begin with, col- ors or patterns that were capable of mimetic development; evidently the raw material must have been present. Now Muller and Dixey in particular have called attention to the fact that many pierids have at least touches of the reds, yellows and other colors that are so conspicuous in the heliconids. More than this, however, Dixey has demonstrated—as appears clearly from his colored figures—a complete and gradual tran- sition from a typical non-mimetic pierid, Pieris locusta, to the mimetic pierid Mylothris pyrrha, the female of which imitates Hehconius numata. He traces the transition chiefly through the males of several pierid species—for the males, though for the most part white (the typical pierid color), ‘‘ show on the under surface, though in varying degrees, an approach towards the Heliconine pattern that is so completely imitated by their mates. These partially developed features on the under sur- face of the males [compare Figs. 2 and 3 of Frontispiece] en- able us to trace the history of the growth of the mimetic pat- tern.” Starting from Pieris locusta, it is an easy step to Mylothris lypera, thence to M. lorena, and from this to the mimetic M. pyrrha. “ Granted a beginning, however small, 234 EN TOMOLOGY such as the basal red touches in the normal Pierines, an elabo- rate and practically perfect mimetic pattern may be evolved therefrom by simple and easy stages.” Furthermore (in answer to the second question), it does not tax the imagination to admit that any one of these color pat- terns has—at least occasionally—been sufficiently suggestive of the heliconid type to preserve the life of its possessor; espe- cially when both bird and insect were on the wing and perhaps some distance apart, when even a momentary flash of red or yellow from a pierid might be enough to save it from attack. It is highly desirable, of course, that this plausible explana- tion should be tested as far as possible by observations in the field and by experiments as well. Adaptive Colors in General.—Several classes of adaptive colors have been discriminated and defined by Poulton, whose classification, necessarily somewhat arbitrary but nevertheless very useful, is given below, in its abridged form. I. APATETIC COLORS.—Colors resembling some part of the en- vironment or the appearance of another species. A. Cryptic CoLtors.—Protective and Aggressive Resemblances. 1. Procryptic colors.—Protective Resemblances.—Conceal- ment as a protection against enemies. Example: Kal- lima butterfly. 2. Anticryptic colors—Aggressive Resemblances.—Conceal- ment in order to facilitate attack. Example: Mantids with leaf-like appendages. B. PseuposemMaAtTic Cotors.—False warning and signalling colors. 1. Pseudaposematic colors—Protective Mimicry. Example: Bee-like fly. 2. Pseudepisematic colors —Aggressive Mimicry and Allur- ing Coloration. Examples: Volucella, resembling bees (Fig. 246); Flower-lke mantid. Il. SEMATIC COLORS.—Warning and Signalling Colors. 1. Aposematic colors—Warning Colors. Examples: Gaudy colors of stinging insects. 2. Episematic colors —Recognition Markings. Ill. EPIGAMIC COLORS.—Colors Displayed in Courtship. Such of these classes as have not already been discussed need brief reference. ADAPTIVE COLORATION 235 Fic. 246. Aggressive mimicry. On the left, a bee, Bombus mastrucatus; on the right, a fly, Volucella bombylans. Natural size. Aggressive Resemblances.—The resemblance of a car- nivorous animal to its surroundings may not only be protec- tive but may also enable it to approach its prey undetected, as in the case of the polar bear or the tiger. Among insects, however, the occurrence of aggressive resemblance is rather doubtful, even in the case of the leaf-like mantids. Ageressive Mimicry.—Under this head are placed those cases in which one species mimics another to which it is hostile. The best known instance is furnished by European flies of the genus Volucella, whose larve feed upon those of bumble bees and wasps. The flies bear a close resemblance to the bees, owing to which it is supposed that the former are able to enter the nests of the latter and lay their eggs. Alluring Coloration.—The best example of this phenom- enon is afforded by an Indian mantid, Gongylus gongyloides, which resembles so perfectly the brightly colored flowers among which it hides that insects actually fly straight into its clutches. Recognition Markings.—Though these are apparently im- portant among mammals and birds, as enabling individuals of the same species quickly to recognize and follow one another, no special markings for this purpose are known to occur among insects, not excepting the gregarious migrant species, such as Anosia plexippus and the Rocky Mountain locust. Epigamic Colors.—Among birds, frequently, the bright col- ors of the male are displayed during courtship, and their evo- 236 ENTOMOLOGY lution has been attributed by Darwin and many of his follow- ers to sexual selection—a highly debatable subject. Among insects, however, no such phenomenon has been found; when- ever the two sexes differ in coloration the difference does not appear to facilitate the recognition of even one sex by the other. Evolution of Adaptive Coloration.—Natural selection is the only theory of any consequence that explains the highly involved phenomena of adaptive coloration. Against such vague and unsupported theories as the action of food, climate, laws of growth or sexual selection, natural selection alone accounts for the multitudinous and intricate correlations of color, pattern, form, attitude, movement, place, time, etc., that are necessary to the development of a perfect case of protective resemblance or mimicry. Natural selection cannot, of course, originate colors or any other characters, its action being re- stricted to the preservation and accumulation of such advan- tageous variations as may arise, from whatever causes. As Poulton says, the vast body of facts, utterly meaningless under any other theory, become at once intelligible as they fall har- moniously into place under the principle of natural selection, to which, indeed, they yield the finest kind of support. (Clabeyie dane Aye ORIGIN OF ADAPTATIONS AND OF SPECIES 1. ADAPTATIONS Organic Evolution.—Organic evolution is essentially the evolution of adaptive structures and functions. There remain to be explained, however, non-adaptive structures and func- tions, and no theory of evolution 1s adequate which does not account for the useless as well as the useful characters. Existing structures are due to the nature of the organism and the nature of the environment; in other words, are results of the activity of protoplasm under the influence of environ- mental forces. Variations arise which are useful or not and either transmissible or not. Useful transmissible variations not only remain but tend to become more nearly perfect ; while useless variations tend to disappear. The various theories of organic evolution differ chiefly in their answers to these questions: (1) What is the nature of variations and how do they arise? Variations are classed as either continuous or discontinuous; adaptive or unadaptive. In asexual organisms, variations are brought about by the direct influence of temperature, light and other primary fac- tors upon protoplasm; in sexual organisms, variations are due to another cause as well, namely, the union of two kinds of protoplasm. In any given case of variation, how much is due immediately to protoplasm and how much to the environment ? (2) What kinds of variations are transmissible? Discontinu- ous variations (sports) are strongly transmissible as a rule, while continuous (individual) variations are often non-trans- missible; though it is often difficult to decide whether they are transmissible or not. Each kind of variation has to be exam- ined separately, on its own merits. Difficulties arise from the 237 238 ENTOMOLOGY fact that some variations which appear in successive genera- tions are due not to inheritance but to the direct action of the environment on each successive generation; also to the fact that some structural changes may have been brought about by selection of some sort, rather than by inheritance. Are the results of use or disuse or mutilation inheritable? It has not been proved as yet that these “acquired characters” are transmissible. On the other hand, experiments show that some organisms can become acclimatized to unusual degrees of heat, density, etc., through inheritance, in cases where selec- tion does not enter into the problem. Much of the confusion attending the discussion of “the inheritance of acquired char- acters’ has been due to disagreements as to what is meant by the term “‘acquired characters.” (3) What are the secondary influences that have brought about the evolution of structures ? Of these influences, natural selection and isolation are by far the most important; while in some instances extensive struc- tural adaptations have arisen spontaneously, without a long course of evolution. Natural Selection.—The more intricate adaptations of organism to environment, however, are for the most part inex- plicable without the aid of Darwin’s and Wallace’s theory of natural selection. After almost fifty years of searching criti- cism and even violent opposition, this theory, though modified in some respects, remains essentially as it was formulated, and is at present the working hypothesis of most naturalists. This doctrine is here outlined in its several factors. Excessive Multiplication.—Any one species of animal or plant, were its multiplication unchecked, would soon cover the earth. The progeny of a single aphid in ten generations; as calculated by Huxley, would “ contain more ponderable sub- stance than five hundred millions of stout men; that is, more than the whole population of China.” The hop aphid (Phor- odon humuli), studied by Riley, has thirteen generations a year, consisting entirely of females up to the last generation. Assuming that each female produces 100 young and that the ORIGIN OF ADAPTATIONS AND OF SPECIES 239 increase is unchecked, the number of individuals of the twelfth generation, as the descendants of a single female of the first generation, would be ten sextillions. These if placed in a single file, allowing 10 aphids to an inch, would form a line so long that light itself, traveling at the rate of 186,000 miles per second, would require over 2,690 years to go from one end of the line to the other. As it is, many species become temporarily dominant under favorable conditions; for example, the Rocky Mountain locust, chinch bug and gypsy moth. Even one of the least prolific species would predominate in a surprisingly short time, were it permitted to increase in its normal geometrical ratio. The rate of sexual reproduction 1s highest in fishes and insects. An insect averages one or two hundred eggs, while some forms, as queen termites, lay them by thousands. Struggle for Existence.—Although a single species is potentially capable of covering the earth, there actually are at least 1,000,000 species of insects, not to mention 250,000 spe- cies of other animals and some 500,000 kinds of plants. This means a tremendous prevention of reproduction among the individuals of any one species—an intense “ struggle for ex- istence,’ as Darwin termed it. Among plants and the lower animals, comparatively few individuals survive and reproduce; the majority die. The agents of destruction are manifold, each species having its own army of enemies, organic and in- ‘ organic. Thus insects are subject to unfavorable conditions of temperature and moisture, to bacterial and fungous dis- eases, vertebrate and invertebrate enemies, accidents, etc. The aphids are at the same time among the most prolific and the most defenceless of animals. ‘These delicate insects suc- cumb to very slight mechanical shocks and are killed by ex- tremes of temperature that most other insects can endure. They are often washed off their food plants by rain. Their rate of reproduction decreases if their food plant receives in- sufficient moisture. Aphids form the chief food of coccinellid larvee and beetles, are preyed upon by chrysopid and syrphid 240 ENTOMOLOGY larvee, parasitized by Braconidz and Chalcidide, carried off by some of the digger-wasps (Muimeside, Pemphredonide), and devoured by ants, carabids, other insects, spiders, and some birds, as the chickadee. In damp weather, aphids are killed in countless numbers by a fungous disease. In short, the aphid is threatened in every direction. Elimination of the Unfit.—In the intense “ struggle for existence,’ as it 1s commonly, though misleadingly, called, those comparatively few individuals that survive do so mani- festly by virtue of certain advantages over their less fortunate fellows. One egg can stand a little more cold than another; one beetle drops to the ground when disturbed and thus escapes an attacking bird, while its companions remain in place and are destroyed; some individuals escape by surpassing their fellows in locomotor ability or by resembling the surface on which they happen to rest. Such fortunate individuals live to transmit their advantage- ous peculiarities to their progeny, while the less favored indi- viduals succumb. The progeny inherit the life-saving pecu- liarities in differing degrees, and the least favored of the progeny are again weeded out. Thus by the continual elim- ination of individuals that vary in unfavorable directions, the individuals that remain become better and better adapted to the surrounding conditions of life, through the preservation and accumulation of advantageous variations. This preser- vation and accumulation of advantageous variations through the destruction of disadvantageous ones is the essence of nat- ural selection, or the “ survival of the fittest.” Favorable variations may have been so slight and infre- quent as to have required geological ages for their accumula- tion. On the other hand, adaptive variations are sometimes so extensive from the beginning as to lead some writers to doubt that these variations are preserved and improved by natural selection. Variation.—Natural selection cannot originate useful char- acters, of course, but is limited to the preservation and accu- ORIGIN OF ADAPTATIONS AND OF SPECIES 24 1 mulation of such advantageous variations as already exist. Variation, then, is the basis of natural selection. Though the question of the origin of variations is still unsettled, the fact of their occurrence in a manner sufficient for the purposes of natural selection is beyond dispute. No two individuals of a species are ever exactly alike in structure or behavior, and their differences furnish the material for the operation of natural selection. Two classes of variations are distinguished on the basis of the amount of variation: (1) continuous (individual) varia- tions, of small extent, intergrading with one another and with the typical form; and (2) discontinuous variations (sports), or considerable and isolated departures from the normal con- dition. Furthermore, variations of either class are adaptive or unadaptive, the latter kind being either harmful or simply neutral. Origin of Adaptive Variations.—Natural selection, as was said, does not begin to operate until useful variations are already in existence; and the origin of these primary adaptive variations is a question quite distinct from that of their sub- sequent preservation and accumulation by natural selection. That all adaptive variations are due to the response of pro- toplasm to environmental influences (using the term “ envi- ronment ” in its widest sense), it goes without saying. These variations are, however, either direct or indirect. Direct variations, appearing first in the soma, or body, of the organ- ism, are termed somatogenic; indirect variations, apparently spontaneous, and due immediately to the germ cells, are termed blastogenic. Weismann places somatogenic variations, ac- cording to their origin, into three categories: (1) myuries, (2) functional variations, and (3) variations depending on the so-called being mainly climatic. These three kinds will receive brief ‘ ‘influences of environment,’ these influences consideration. Injuries.—There appears to be no good evidence that in- juries or mutilations can be transmitted. Nearly all the ex- 17 242 ENTOMOLOGY periments upon the subject have given decidedly negative results. Thus Weismann found that the amputation of the tails of hundreds of mice, down to the nineteenth generation, had no influence on the tails of the descendants. Mechanical injuries to the body of an organism are merely casual, or accidental, effects of the environment and appear to have no influence upon the germ cells. From the standpoint of adaptation, injuries are only of minor importance. Functional Variations.—While it is certain that the use or disuse of organs affects their form in the individual, it | remains doubtful whether the effects of use and disuse are transmissible. Weismann and his followers contend that they are not. On the other hand, Neo-Lamarckians, as Cope, Hyatt, H. F. Osborn, Packard and Eimer, have maintained - that they are. Weismann admits, however, that both use and disuse may lead indirectly to variations, “the former when- ever an increase as regards the character concerned is useful, and the latter in all cases in which an organ is no longer of any importance in the preservation of the species’; and that these variations may be acted upon by natural selection. Thus, in a few words, the question stands. Environmental Variations.—Under this head may be classed such variations as are due directly to climate, nutrition and other primary environmental influences. It is certain that changes of temperature, light, and food, for example, cause corresponding changes of form and function in the indi- vidual organism; though the inheritance of these changes directly induced by the environment is the subject of much debate. Dallinger took flagellate infusorians that at first would die at a temperature of 23° C., and by slowly raising the tempera- ture through several years, brought them safely to a tempera- ture of 70° C. There was some mortality, to be sure, in his experiments, but other experimenters have obtained similar results without the loss of a single individual, and therefore— it is important to note—without the entrance of natural selec- ORIGIN OF ADAPTATIONS AND OF SPECIES 243 tion. ‘This progressive acclimatization of successive genera- tions of an organism to heat is clearly due in large measure to heredity. So also in the case of the entomostracan Artemia, whose specific form Schmankewitsch succeeded in changing, by increasing the salinity of the water in which the animal lived. Here, again, the adaptation was brought about with- out the aid of selection. Poulton’s already-mentioned experiments on larve and pupze show that these may become protectively colored as the direct effect of the surrounding light on the organism. Here, of course, the possible influence of natural selection can scarcely be excluded, though the fact remains that the color resem- blances are initiated directly by the stimulus of light upon protoplasm. Protoplasm itself is to a certain extent adaptive, in that it may become acclimatized to untoward conditions of heat, light and other stimuli. From this point of view, Henslow’s theory of self-adaptation in plants deserves more consideration than it has received, though Henslow did not adopt the theory of natural selection. Blastogenic Variations.—According to Weismann, only congemtal variations are inheritable, 1. e., only those that result from modifications of the germ plasm. He holds that while all variations are due ultimately to external influences, the processes of reproduction (conjugation in unicellular, and sexual reproduction in multicellular organisms) furnish fresh combinations of individual variations for the operation of nat- ural selection, and that this is the chief purpose of amphimixis, or “the mingling of two individuals or of their germs.”’ Inheritance of Acquired Characters.—\Veismann and his followers, in opposition to the Neo-Lamarckians, hold that somatogenic, or acquired, characters are not transmissible; that every permanent (hereditary) variation proceeds from the germ. The subject of the inheritance of acquired characters has aroused no end of discussion, much of which has been fruit- 244 ENTOMOLOGY less, chiefly for two reasons. First, there is no little disagree- ment as to what is meant by the term “ acquired characters.” An acquired character arises, not in the germ cells, but in the soma, or body, and for the theoretical transmission of the character the soma must affect the germ cells subsequently ; though some maintain that a given external influence may affect both soma and germ plasm at the same time. The defi- nition of acquired characters excludes (1) sports; (2) changes due to the renewed action of the environment upon successive generations of an organism; (3) changes which may have been due to selection. Second, having defined the term, it is often difficult if not impossible to say whether a given charac- ter is acquired or not. Thus in an acclimatization experiment, if heat, for example, affects first the soma and the latter affects the germ cells subsequently, we have an example of the inheri- tance of an acquired character. If, however, the heat affects soma and germ plasm simultaneously, the result is or is not the inheritance of an acquired character, according as one de- fines the term. Indeed, Weismann himself has found the greatest difficulty in trying to explain the inheritance of “ cli- matic” variations in terms of his well-known hypothesis. In fact, the distinction between acquired and non-acquired charac- ters is to no little extent artificial and arbitrary; and too strong an insistence upon the distinction bars the way to the solution of the more important question—What kinds of variations are inheritable and what are not? To summarize: Of somatogenic, or acquired, characters, (1) injuries or mutilations are unadaptive and probably unin- heritable. (2) Functional variations are adaptive, but the subject of their transmissibility is involved in doubt. As yet there is no adequate experimental evidence upon the subject, the discussion of which, therefore, is based chiefly on theoret- ical grounds. ‘There is a strong tendency, however, to believe that results of use or disuse are to some extent transmissible to the benefit of succeeding generations, and even Weismann, the chief opponent of the Neo-Lamarckians, admits that the ORIGIN OF ADAPTATIONS AND OF SPECIES 245 effects of use and disuse are important in organic evolution. (3) Effects of climatal influences and of nutrition are fre- quently adaptive and often transmissible, as experiments have proved. There is, however, much difference of opinion as to the precise way in which these effects are transmitted. Incidental Adaptations.—Many leaf-eating caterpillars and grasshoppers are green from the presence of chlorophyll in their bodies; they owe their color directly to their food. Now it may be admitted that this green color is often protec- tive, without admitting that the color was acquired for that purpose. In the case of green leaf-mining caterpillars, cer- tainly, the color appears to be superfluous for protective pur- poses. Even variegated protective coloration may be simply a direct effect of the surrounding kinds of light, as Poulton proved. Again, take the various tropisms, described in another chapter. Often they are adaptive and often they are not; but they occur inevitably, whether they result advantageously or not. It is too much to say that a useful structure or function appeared because of its usefulness. It first appeared, and then proved to be either useful or not useful. If useful, a structure may save the life of its possessor and possibly be transmitted .to the next generation; if harmful, it is self-eliminating. 2. SPECIES Modifications arise, and are either useful or not to their possessors. For the systematist who aims merely to distin- guish one species from another, this distinction matters but little. To the biologist, however, the difference is an essential one, and he draws a line between specific peculiarities that are adaptive and those that are not adaptive. The origin of species and the origin of adaptations are by no means the same thing. Darwin’s Origin of Species.—At the time Darwin’s great work was written, its immediate purpose was to demonstrate a process of organic evolution; and this object was accom- 246 ENTOMOLOGY plished in the most forcible way, namely, by shattering the traditional belief in the immutability of species. Nowhere does Darwin imply that nature is striving to produce “ spe- cies’ for their own sake. A process of evolution was the theme of Darwin and its key-note was adaptation. Indeed, for the purposes of the present generation, Dar- win’s immortal work would more properly be entitled—The Evolution of Adaptations by Means of Natural Selection. And to us, who now ridicule the old notion of the special creation of species, the doctrine of natural selection appears in a fresh light, with a new mission. For, in the words of Romanes, the theory is “ primarily, a theory of adaptations, and only becomes secondarily a theory of species in those com- paratively insignificant cases where the adaptations happen to be distinctive of the lowest order of taxonomic division.” The opposite view he compares “ to that of an astronomer who should define the nebular hypothesis as a theory of the origin of Saturn’s rings. It is indeed a theory of the origimgor Saturn’s rings; but only because it is a theory of the origin of the entire solar system, of which Saturn’s rings form a part. Similarly, the theory of natural selection is a theory of the entire system of organic nature in respect of adaptations, whether these happen to be distinctive of particular species only, or are common to any number of species.”’ It should be remembered, of course, in using this comparison, that not all specific characters are adaptive. As regards the origin of species, however, there are several] processes at work besides natural selection. Indeed, Darwin himself knew this, for he expressly stated: “ I am convinced that natural selection has been the most important, but not the exclusive, means of modification.” The Conception of “Species.”—What is a “species”? The only practical criterion of species is isolation, or separate- “species ”” ‘ ness, of one kind or another. The majority of our are sharply separated from one another by structural differ- ences; the minority, however, blend into one another, and ORIGIN OF ADAPTATIONS AND OF SPECIES 247 have so many characters in common that the separation into species becomes an arbitrary matter, depending upon the good judgment of the systematist, who if wise, is neither-a “Jumper” nor a “splitter.” At present, the minutely dis- criminating powers of an unfortunately large number of ento- mological systematists are displayed in an extraordinary mul- tiplication of generic and specific names, often to the sacrifice of convenience and stability of nomenclature. This has been carried to such an extent, however, that a reaction has already set in, and there is now some promise of a rational termi- nology. Considering characters as of specific importance only, it makes no immediate difference whether they are adaptive or not. If adaptive, whatever their origin, they may have been developed by natural selection; if not, they are incidental, and may be due to such influences as those next to be referred to. Climate and Food.—Naturalists have recorded many in- stances in which plants or animals when transferred to a new climate have produced offspring markedly different from the parent form. The term climate, however, has no precise meaning for the naturalist, referring as it does collectively to several distinct influences, chief among which are tempera- ture, moisture, light and (indirectly) food conditions. Ex- perimental evidence has already been adduced to show that color changes in insects may be brought about as direct effects of warmth, cold, light or food. Some of these color varia- tions are possibly inheritable, and many of them, artificially produced, would be regarded as distinctive of new species, if found in a state of nature. In fact, the distinction between varieties and species is often entirely arbitrary; varieties are incipient species and it is often impossible to draw any sharp line between the two. Mutation Theory.—De Vries’ mutation theory, expounded in 1901 as the result of nearly twenty years of experimenta- tion, is at present an absorbing subject of study and discussion in the biological world, and will continue to be for many years, until the full bearing of the theory is ascertained. 248 ENTOMOLOGY De Vries has produced new species by experimental means and without the aid of selection. Moreover, he has produced them at once, showing that a species does not necessarily re- quire hundreds of years to develop, by means of a long-con- tinued process of selection. It has long been customary to draw a distinction between individual variations and sports. Darwin recognized the dis- tinction and was one of the first to notice the extraordinary persistence with which sports are transmitted, as compared with the relative instability of individual variations. Not a few dominant races of plants and animals are known to have arisen from sports, and the belief has been gaining ground with Bateson and others that species also have to some extent arisen from sports, rather than from individual variations; though the rarity of sports as compared with individual varia- tions is the strongest objection to this theory as a theory of the origin of species in general. De Vries, however, was the first to make extensive experi- ments on sports, or mutations, as he calls them, and to formu- late a definite theory of the subject from a considerable body of evidence. He regards the qualities of organisms as being built up of definite but sharply separated units, or elements, which combine in groups. The addition of a new unit means a mutation, a sudden departure from the normal specific form; in other words, a new species may arise from the parent form without any evident gradation. The mutable condition exists only at times, and some species are more mutable than others. Acting upon this as a hypothesis, De Vries made a preliminary study of a great number of plants in order to find one in its period of mutation, and at length selected Ginothera Lamarck- tana (probably a variety of our E. biennis, introduced into Holland from America), because of its exceptionally vigorous multiplication, dispersion and variation. By careful cultivation and by means of artificial pollination, he succeeded in obtaining seven or more new species. Most of these remained con- stant from year to year in spite of intercrossing. Moreover, ORIGIN OF ADAPTATIONS AND OF SPECIES 249 cross pollination was not necessary to the production of new species by mutation, and when employed did not accelerate the results materially. As a botanist, De Vries confined his inves- tigations to plants, but his general conclusions are perhaps equally applicable to animals, and his experiments are doubt- less being repeated by zoologists. Through his exhaustive experiments, De Vries has partly attained a long-desired object, in that he has removed the ques- tion of the origin of some species “ from the purely theoretical pomene concrete. The mutation theory is not primarily a theory of the origin of adaptive characters. It endeavors to account for the origin of certain characters, which may or may not prove useful to their possessors. Indeed, one great merit of De Vries’ theory is that it affords an explanation for the existence of variations which are not useful. Now Darwin does not pretend to account for the origin of variations, but he shows how given variations, if useful, may be preserved and accumulated. Thus the theory of De Vries supplements that of Darwin and does not antagonize it; even though De Vries himself takes much pains to contrast the two theories, and even asserts that new species arise exclusively as mutations. Both theories, indeed, are theories of the origin of species; but according to De Vries, specific characters spring into existence, irrespective of their usefulness; while according to Darwin, useful characters, and these only, are premised, as the starting point of the evolu- tion of certain kinds of species. Thus, as another has said, natural selection begins where the mutation theory leaves off. Isolation.—The theory of isolation as given by Gulick and by Romanes is highly important as affording an explanation of “ the rise and continuance of specific characters which need not necessarily be adaptive characters.” By isolation is meant “simply the prevention of intercrossing between a separated section of a species or kind and the rest of that species or kind. . . . So long as there is free intercrossing, heredity cancels variability, and makes in favor of fixity of type. Only 250 ENTOMOLOGY when assisted by some form of discriminate isolation, which determines the exclusive breeding of like with like, can hered- ity make in favour of change of type, or lead to what we un- derstand by organic evolution.” (Romanes. ) “As soon as a portion of a species is separated from the rest of that species, so that breeding between the two portions is no longer possible, the general average of characters in the separated portion not being in all respects precisely the same as it is in the other portion, the result of in-breeding among all individuals of the separated portion will eventually be dif- ferent from that which obtains in the other portion; so that, after a number of generations, the separated portion may become a distinct species from the effect of isolation alone. Even without the aid of isolation, any original difference of average characters may become, as it were, magnified in suc- cessive generations, provided that the divergence is not harm- ful to the individuals presenting it, and that it occurs in a sufficient proportional number of individuals not to be imme- diately swamped by intercrossing.” (Romanes. ) Of the many modes of isolation, the most important are the geographical and the physiological, both of which have re- ceived elaborate treatment by Romanes. The doctrine of geographical isolation offers a partial ex- planation of the origin of the peculiar faunze and flore of remote islands. These island species, however peculiar, doubtless came originally from the mainlands where their nearest allies now occur; thus the endemic insects of the Gala- pagos Islands are most nearly related to species of western South America. The first individuals of Schistocerca doubtless reached the Galapagos Islands by means of the wind or on driftwood. These individuals, separated from the main body of their spe- cies, would interbreed and might thereby give rise to a new variety or species, if we may assume that the average of charac- ters of the detached portion of the species differed from that of the main body of individuals; in other words, that the iso- ORIGIN OF ADAPTATIONS AND OF SPECIES 251 lated forms varied around a mean condition of their own, and no longer around the mean of the species as a whole. Besides this, the influences of new food and new climatal con- ditions as means of modification must be taken into account. Furthermore, though a new species might conceivably arise on an island without the aid of natural selection, it is very likely that selection has often played a part in the formation of such a species, as in the apterous or subapterous forms that pre- dominate on oceanic islands. While it is possible that the earliest arrivals were already apterous, and arrived safely be- cause on that account they clung to driftwood instead of flying away, it is probable, on the other hand, that on wind-swept islands the full-winged and more venturesome individuals would be carried out to sea and drowned, leaving the poorly winged and less venturesome ones to remain and transmit their own life-saving peculiarities; which would become inten- sified by continual selection of the same kind. Romanes, in- deed, regards natural selection itself as but one form of iso- lation. Physiological isolation, which though important will not be discussed here, “arises in consequence of mutual infertility between the members of any group of organisms and those of all other similarly isolated groups occupying simultaneously the same area.”’ (Romanes. ) C PLACE AER Weald INSECTS IN.RELATION TO PLANTS Insects, in common with other animals, depend for food primarily upon the plant world. No other animals, however, sustain such intimate and complex relations to plants as in- sects do. The more luxuriant and varied the flora, the more abundant and diversified is its accompanying insect fauna. Not only have insects become profoundly modified for using all kinds and all parts of plants for food and shelter, but plants themselves have been modified to no small extent in relation to insects, as appears in their protective devices against unwelcome insects, in the curious formations known as “ galls,” the various insectivorous plants, and especially the omnipresent and often intricate floral adaptations for cross-pollination through the agency of insect visitors. Though insects have laid plants un- der contribution, the latter have not only vigorously sustained the attack but have even pressed the enemy into their own ser- vice, as it were. Numerical Relations.—The number of insect species sup- ported by one kind of plant is seldom small and often surpris- ingly large. The poison ivy (Rhus toxicodendron) is almost exempt from attack, though even this plant is eaten by a leaf- mining caterpillar, two pyralid larve and the larva of a scolytid beetle (Schwarz, Dyar). Horse-chestnut and buckeye have per- haps a dozen species at most; elm has eighty ; birches have over one hundred, and so have maples; pines are known to harbor 170 species and may yield as many more; while our oaks sus- tain certainly 500 species of insects and probably twice as many. Turning to cultivated plants, the clover is affected, directly or indirectly, by about 200 species, including predaceous insects, parasites, and flower-visitors. Clover grows so vigorously that 25 to INSECTS IN RELATION TO PLANTS 253 it is able to withstand a great deal of injury from insects. Corn is attacked by about 200 species, of which 50 do notable injury and some 20 are pests. Apple insects number some 400 species. Not uncommonly, an insect is restricted to a single species of plant. Thus the caterpillar of Heodes hypophleas feeds only on sorrel (Rume-x acetosella), so far as is known. The chry- somelid Chrysochus auratus appears to be limited to Indian hemp (Apocynum androsenifolium) and to milkweed (As- clepias). In many instances, an insect feeds indifferently upon several species of plants provided these have certain attributes in common. Thus Argynnis cybele, aphrodite and atlantis eat the leaves of various species of violets, and the Colorado potato beetle eats different species of Solanum. Papilio thoas feeds upon orange, prickly ash and other Ruta- cee. Anosia plexippus eats the various species of Asclepias and also Apocynum androsenuifolium; while Chrysochus also is limited to these two genera of plants, as was said. These plants agree in having a milky juice; in fact the two genera are rather nearly related botanically. The common cab- bage butterfly (Pieris rape) though confined for the most part to Cruciferze, such as cabbage, mustard, turnip, radish, horse- radish, etc., often develops upon Trope@olum, which belongs to Geraniacee ; all its food plants, however, have a pungent odor, which is probably the stimulus to oviposition. Most phytophagous insects, however, range over many food- plants. The cecropia caterpillar has more than sixty of these, representing thirty-one genera and eighteen orders of plants; and the tarnished plant bug (Lygus pratensis) feeds indiffer- ently on all sorts of herbage, as does also the caterpillar of Diacrisia virginica. Many of the insects of apple, pear, quince, plum, peach, and other plants of the family Rosaceze occur also on wild plants of the same family; and the worst of our corn and wheat insects have come from wild grasses. As regards number of food plants, the gypsy moth “holds the record,” for its caterpillar will eat almost any plant. In Mass- achusetts, according to Forbush and Fernald, it fed in the field 254 ENTOMOLOGY upon 78 species of plants, in captivity upon 458 species (30 under stress of hunger, the rest freely), and refused only 19 species, most of which (such as larkspur and red pepper) had poisonous or pungent juices, or were otherwise unsuit- Holcaspis globulus. A, galls on oak, natural size; B, the gall-maker, twice natural length. able as food. The migratory locust is notoriously omnivy- orous, and perhaps eats even more kinds of plants than the gypsy moth. Galls.—Most of the conspic- uous plant_outgrowths known as oe galls’ are made by in- sects, though many of the smaller plant galls are made by mites (Acarina) and a few plant excrescences are due to nematode worms and to fungi. Among insects, Cynipide (Hy- menoptera) are pre-eminent as -gall-makers and next to these, Cecidomyiidz (Diptera), Aphididz and Psyllide (Hemiptera) ; a few gall-insects occur Fic. 248. Galls of Holcaspis duricoria, on oak. Natural size. among Tenthredinidz (Hymenoptera) and Trypetidze (Dip- tera), and one_or two antong Coleoptera and Lepidoptera. Cynipide affect the oaks (Figs. 247, 248) far more often INSECTS IN RELATION TO PLANTS No unr un than any other plants, though not a few species select the wild rose. Cecidomyiid galls occur on a great variety of plants, and those of aphids on elm (Fig. 249), poplar, and many other plants; while psyllid galls are most frequent on hackberry. The galls may occur anywhere on a plant, from the roots to the flowers or seeds, though each gall-maker always works on the same part of its plant,—root, stem, bud, leaf, leaf-vein, flower, seed, etc. Galls present innumerable forms, but the form and situation of a gall are_usually—characteristic, so that it is Often possible to classify galls as_species even before the gall-maker is known. Gall-Making.—The female cy- nipid punctures the plant and lays an egg in the wound; the egg hatches and the surrounding plant FIG. 249. tissue is stimulated to grow rapidly and abnormally into a gall, which serves as food for the larva; this transforms within the gall and es- capes as a winged insect. The physiology of gall-formation is far Cockscomb gall of Colopha ulmicola, Sas on elm. Slightly reduced. from being understood. It has been found that the mechanical irritation from the ovipositor is not the initial stimulus to the development of a gall; neither is the fluid which is injected by the female during oviposition, this fluid being probably a lubricant ; if the egg is removed, the gall does not appear. Ordinarily the gall does not begin to grow until the egg has-hatched, and then the gall grows along with the larva; exceptions to this are found in some Hymenoptera in which the egg itself increases in volume, when the gall may grow with the ege. It appears that the larva exudes some fluid which acts upon the protoplasm of certain plant cells (the cambium and other cells capable of further growth and multi- plication) in such a way as to stimulate their increase in size 256 ENTOMOLOGY and number. Why the gall should have a distinctive, or spe- cific, form, it is not yet known. There is no evidence that the form is of any adaptive importance, and the subject probably admits of a purely mechanical explanation — a problem for the future. Gall Insects. — The study of gall insects is in many respects. difficult. It is not at all certain that an insect which emerges from a gall is the species that made it; for many species, even of Cynipidz, make no galls themselves but lay their eggs in galls made by other species. Such guest-insects are termed inguilines. Furthermore, both gall-makers and inquilines are attacked by parasitic Hymenoptera, making the interrelations of these insects hard to determine. Many species of insects feed upon ‘the substance of galls; thus Sharp speaks of as many as thirty different k kinds of insects, belonging to o nearly all the orders, as having” been reared from a single species of gall. Parthenogenesis and Alternation of Generations.—Par- thenogenesis has long been known to occur among Cynipide. It has repeatedly been found that of thousands of insects emerging from galls of the same kind, all were females. In one such instance the females were induced by Adler to lay eggs on potted oaks, when it was found that the resulting galls were quite unlike the original ones, and produced both sexes of an insect which had up to that time been regarded as another species. Besides parthenogenesis and this alternation of gene- rations, many other complications occur, making the study of gall-insects an intricate and highly interesting subject. Plant-Enemies of Insects.—Most of the flowering plants are comparatively helpless against the attacks of insects, though insects 9 there are many devices which prevent “unwelcome from entering flowers, for instance the sticky calyx of the catch- fly (Silene virginica), which entangles ants and small flies. A few plants, however, actually feed upon insects themselves. Thus the species of Drosera, as described in Darwin’s classic volume on insectivorous plants, have specialized leaves for the INSECTS IN RELATION TO PLANTS 257 purpose of catching insects. The stout hairs of these leaves end each in a globular knob, which secretes a sticky fluid. When a fly alights on one of these leaves the hairs bend over and hold the insect; then a fluid analogous to the gastric juice of the human stomach exudes, digests the albuminoid substances of the insect and these are absorbed into the tissues of the leaf; after which the tentacles’ unfold and are ready for the next insect visitor. The Venus’s flytrap is another well- known example; the trap, formed from the terminal portion of a leaf, consists of two valves, each of which bears three trigger-like bristles, and when these are touched by an insect the valves snap to- gether and frequently imprison the insect, which is eventually digested, as before. In the common pitcher-plants, the pitcher, fashioned from a leaf, is lined with down- ward pointing bristles, which allow an insect to enter but prevent its escape. The bottom of the pitcher contains water, in which may be found the remains of a great variety of insects which have drowned. There are even nectar glands and conspicuous colors, presum- ably to attract insects into these traps, Fructifying sprouts of where their decomposition products are a fungus, Cordyceps rave- nelii, arising from the In body of a white grub, mowtcula are UAE af rolls Lachnosterna. Slightly Pinguicula the margin of a leaf Ee aie ee over and envelops insects that have been caught by the glandular hairs of the upper surface more or less useful to the plant. of the leaf, a copious secretion digests the softer portions of the insects, and the dissolved nitrogenous matter is absorbed into the plant. Utricularia has little bladders which entrap small aquatic insects. These plants are only partially depend- 18 258 ENTOMOLOGY ent on insect-food, however, for they all possess chlorophyll. Bacteria cause epidemic diseases among insects, as in the flacherie of the silkworm; and fungi of a few groups are spe- cially adapted to develop in the bodies of living insects. Those who rear insects know how frequently caterpillars and other larve are destroyed by fungi that give the insects a powdered appearance. These fungi, referred to the genus Tsaria, are in some cases known to be asexual stages of forms of Cordyceps, which forms appear from the bodies of various larvee, pupze and imagines as long, conspicuous, fructifying sprouts (Fig. 250). The chief fungus parasites of insects belong to the large family Entomophthoracez, represented by the common Empusa musce (Tig. 251) which affects various flies. In autumn, Ge 25ir Empusa musce, the common fly-fungus. A, house fly (Musca domestica), sur- rounded by fungus spores (conidia); B, group of conidiophores showing conidia in several stages of development; C, basidium (b) bearing conidium (c) before discharge. B and C after THAXTER. especially in warm moist weather, the common house fly may often be seen in a dead or dying condition, sticking to a win- dow-pane, its abdomen distended and presenting alternate black and white bands, while around the fly at a little distance is a INSECTS IN RELATION TO PLANTS 259 white powdery ring, or halo. The white intersegmental bands are made by threads of the fungus just named, and the white halo by countless asexual spores known as conidia, which have been forcibly discharged from the swollen threads that bore them (Fig. 251) by pressure, resulting probably from the ab- sorption of moisture. These spores, ejected in all directions, may infect another fly upon contact and produce a growth of fungus threads, or hyphe, in its body. The fungus may be propagated also by means of resting spores, as found by Thax- ter, our authority upon the fungi of insects. Empusa aphidis is very common on plant lice and is an im- portant check upon their multiplication. Aphids killed by this fungus are found clinging to their food plant, with the body swollen and discolored. Empusa grylli attacks crickets, grass- hoppers, caterpillars and other forms. Curiously enough, grasshoppers affected by this fungus almost always crawl to the top of some plant and die in this conspicuous position. Sporotrichum, a genus of hyphomycetous fungi, affects a great variety of insects, spreading within the body of the host and at length emerging to form on the body of the insect a dense white felt-like covering, this consisting chiefly of myriads of spores, by means of which healthy insects may become in- fected. Under favorable conditions, especially in moist sea- sons, contagious fungus diseases constitute one of the most important checks upon the increase of insects and are therefore of vast economic importance. Thus the termination (in 1889) of a disastrous outbreak of the chinch bug in Illinois ‘ and neighboring states “was apparently due chiefly, if not altogether, to parasitism by fungi.” Artificial cultures of the common Sporotrichum globuliferum have been used exten- sively as a means of spreading infection among chinch bugs and grasshoppers, with, however, but moderate success as yet. Insects in Relation to Flowers.— Among the most marve- lous phenomena known to the biologist are the innumerable and complex adaptations by means of which flowers secure cross pollination through the agency of insect visitors. 260 EN TOMOLOGY Cross fertilization is actually a necessity for the continued vigor and fertility of flowering plants, and while some of them are adapted for cross pollination by wind or water, the major- ity of flowering plants exhibit profound modifications of floral structure for compelling insects (and a few other animals, as birds or snails) to carry pollen from one flower to another. In general, the conspicuous colors of flowers are for the purpose Bumble bee (Bombus) entering flower of blue-fiag ([ris versicolor). Slightly reduced. of attracting insects, as are also the odors of flowers. Night- blooming flowers are often white or yellow and as a rule strongly scented. Colors and odors, however, are simply indications to insects that edible nectar or pollen is at hand. Such is the usual statement, and it is indeed probable that INSECTS IN RELATION TO PLANTS 261 insects actually do associate color and nectar, even though they will fly to bits of colored paper almost as readily as they will to flowers of the same colors. It is not to be supposed, however, that insects realize that they confer any benefit upon the plant in the flowers of which they find food. At any rate, most flowers are so constructed that certain insects cannot get the nectar or pollen \ without carrying some pollen = p.-----~ : away, and cannot enter the next flower of the same kind without leaving some of this pollen upon the stigma of that flower. Take the iris, for example, which is admirably adapted for pollina- tion by a few bees and flies. Iris—In the common blue-flag (Jris versicolor, Fig. 252), each of the three drooping sepals forms the floor of an arched passageway leading to the nec- tar. Over the entrance and pointing outward is a movable lip (Fig. 253, 7), the outer surface of which is stigmatic. An entering bee hits and bends down the free edge of this lip, which scrapes pollen from the back of the insect and then springs back into place. Within the passage, the Section to illustrate cross pollination hairy back of the beerubs against - eo ae ae Scag a an overhanging anther(am). and becomes powdered with grains of pollen as the insect pushes down towards the nectar. As the bee backs out of the pass- age it encounters the guardian lip again, but as this side of the lip can not receive pollen, immediate close pollination is prevented. Of course, it is possible for bees to enter another part of the same flower or another flower of the same plant, but as a matter of fact, they habitually fly away to another plant; moreover, as Darwin found, foreign pollen is prepotent over pollen from the same flower. It may be added that bees 262 ENTOMOLOGY and other pollenizing insects ordinarily visit in succession sev- eral flowers of the same kind. Orchids.—The orchids, with their fantastic forms, are really elaborate traps to insure cross pollination. In some orchids (Habenaria and others) the nectar, lying at the bottom of a long tube, is accessible only to the long-tongued Sphingide. While probing for the nectar, a sphinx moth brings each eye against a sticky disk to which a pollen mass is attached, and flies away carrying the mass on its eye. Then these pollinia bend down on their stalks in such a way that when the moth thrusts its head into the next flower they are in the proper position to encounter and adhere to the stigma. The orchid Angrecum sesquipedale, of Madagascar, has a nectary tube more than eleven inches long, frem which Darwin inferred the. existence of a sphinx moth with a tongue equally long,—an inference which proved to be correct. Milkweed.—The various milkweeds are fascinating subjects to the student of the interrelations of flowers and insects. The flowers, like those of orchids, are remarkably formed with Fig. 254. Structure of milkweed flower (Asclepias incarnata) with reference to cross pollina- tion. A, a single flower; c, corolla; h, hood; B, external aspect of fissure (f) leading up to disk and also into stigmatic chamber; hh, hood; C, pollinia; d, disk. Enlarged. INSECTS IN RELATION TO PLANTS 263 reference to cross pollination by insects. As a honey bee or other insect crawls over the flowers (Fig. 254, 4) to get the nectar, its legs slip in between the peculiar nectariferous hoods situated in front of each anther. Asa leg is drawn upward one of its claws, hairs, or spines frequently catches in a V-shaped fissure (f, Fig. 254, B) and is guided along a slit to a notched Wisieeor corpuscle (Fig. 254, C, d). Whis disk clings to the leg of the insect, which carries off by means of the disk a pair of pollen masses of pollima (Fig. 254, C). When first re- moved from their enclosing pockets, or anthers, these thin spatulate pollinia lie each pair in the same plane, but in a few minutes the two pollinia twist on their stalks and come face to face in such a way that one of them can be easily introduced into the stigmatic chamber of ~ a new flower visited by the in- sect. Then the struggles of the insect ordinarily break the stem, or retinaculum, of the pollinitum and free the insect. Often, however, the insect loses a leg or else is permanently entrapped, particularly in the case of such _ large-flowered milkweeds as Asclepias cornutt, MieMmotben captures bees, fies: a WascoSphex: schneumonea, with pol- aidmaouis of considerable size, Ht of -milkweed. attached to its legs. Slightly enlarged. Pollination is accomplished by a great variety of insects, chiefly Hymenoptera, Diptera, Lepi- doptera and Coleoptera. These insects when collected about milkweed flowers usually display the pollinia dangling from their legs, as in Fig. 255. The details of pollination may be gathered by a close ob- server from observations in the field and may be demonstrated to perfection by using a detached leg of an insect and dragging it upward between two of the hoods of a flower; first to re- move the pair of pollinia and then again to introduce one of them into an empty stigmatic chamber. 264 ENTOMOLOGY Yucca.—An extraordinary example of the interdependence of plants and insects was made known by Riley, whose detailed account is here summarized. The yuccas of the southern United States and Mexico are among the few plants that depend for pollination each upon a single species of insect. The pollen of Yucca flamentosa cannot be introduced into the stigmatic tube of the flower without the help of a little white tineid moth, Pronuba yuccasella, the female of which pollen- izes the flower and lays eggs among the ovules, that her larve Fic. 256. may feed upon the young seeds. While the male has no un- usual structural pecu- liarities, the female is. adapted for her special work by modifications which “are Wntqmine among Lepidoptera, namely, a pair of pre- hensile and _— spinous maxillary “tentacles ” (Fig. 256,-°4) Panes long protrusible ovi- Promuba yucca. Ay maxillary tentade POSIOT, 9 C3 Ramus and palpus; B, ovipositor.—After Ritey. Fig- e@ombines in itself the ures 256-258 are republished from the Third _ Report of the Missouri Botanical Garden, by functions of a lance a ae and a saw. The female begins to work soon after dark, and will con- tinue her operations even in the light of a lantern. Clinging to a stamen (Fig. 257) she scrapes off pollen with her palpi and shapes it into a pellet by using the front legs. After gathering pollen from several flowers she flies to another flower, as a rule, thrusts her long flexible ovipositor into the ovary (Fig. 258) and lays a slender egg alongside seven or eight of the ovules. After laying one or more eggs she ascends INSECTS IN RELATION TO PLANTS i) oO" wal the pistil and actually thrusts pollen into the stigmatic tube and pushes it in firmly. The ovules develop into seeds, some of which are consumed by the larve, though plenty are left to perpetuate the plant itself. Three species of Pronuba are known, each restricted to particular species of Yucca. Riley says that Yucca never produces seed where Pronuba does not occur or where she is excluded artificially, and that artificial pollination is rarely so success- ful as the normal method. Why does the insect do this? The ht- tle nectar secreted at the base of the pistil appears to be of no consequence, at pres- ent, and the stigmatic fluid is not necta- rian; indeed, the tongue of Pronuba, used in clinging to the stamen, seems to have lost partially or entirely its sucking power, WSS SS AR “s Pronuba yuccasella, fe- male, gathering pollen from anthers of Yucca. Enlarged. and the alimentary canal is regarded as functionless. Ordina- Pronuba moth ovipositing in flower of Yucca. Slightly reduced. rily it is the flower which has become adapted to the insect, which is enticed by means of pollen or nectar, but here is a 266 ENTOMOLOGY flower which—though entomophilous in general structure—has apparently adapted itself in no way to the single insect upon which it is dependent for the continuance of its existence. More than this, the insect not only labors without compensation in the way of food, but has even become highly modified with refer- ence to the needs of the plant,—its special modifications being unparalleled among insects with the exception of bees, and being more puzzling than the more extensive adaptations of the bees when we take into consideration the impersonal nature of the operations of Pronuba. Further investigation may render these extraordinary interrelations more intelligible, or less mysterious, than they are at present. The bogus Yucca moth Fic. 259. (Prodoxus quinquepunc- tella) closely resembles and associates with Pro- nuba but oviposits in the flower stalks of Yucca and has none of the spe- cial adaptive structures found in Pronuba. As regards floral adap- tations, these examples are sufficient for present purposes; many others have been described by the botanist; in fact, the adaptations for cross pol- Phiceethontius sezta visiting Aower of Petunia, Mtation by imseutspaemas Reduced. varied as the flowers them- selves. Insect Pollenizers.—The great majority of entomophilous flowers are pollenized by bees of various kinds; the apple, pear, blackberry, raspberry and many other rosaceous plants depend chiefly upon the honey bee, while clover cannot set seed without the aid of bumble bees or honey bees, assisted possibly INSECTS IN RELATION TO PLANTS 267 by butterflies. Lilies and orchids frequently employ butterflies and moths, as well as bees, and the milkweed is adapted in a remarkable manner for pollination by butterflies, moths and some wasps, as was described. Honeysuckle, lilac, azalea, tobacco, Petunia, Datura and many other strongly scented and conspicuous nocturnal flowers attract for their own uses the Fic. 260. A butterfly, Polites peckius, stealing nectar from a flower of Iris versicolor. Slightly reduced. long-tonged sphinx moths (Fig. 259) ; the evening primrose, like milkweed, is a favorite of noctuid moths. Umbelliferous plants are pollenized chiefly by various flies, but also by bees and wasps. Pond lilies, golden rod and some other flowers are pollenized largely by beetles, though the flowers exhibit no special modifications in relation to these partictilar insects. It 268 ENTOMOLOGY is noteworthy that pollination is performed only by the more highly organized insects, the bees heading the list. Of all the insects that haunt the same flower, it frequently happens that only a few are of any use to the flower itself; many come for pollen only; many secure the nectar illegiti- mately ; thus bumble bees puncture the nectaries of columbine, snapdragon and trumpet creeper from the outside, and’ wasps of the genus Odynerus cut through the corolla of Pentstemon levigatus, making a hole opposite each nectary; then there are the many insects that devour the floral organs, and the insects which are predaceous or parasitic upon the others. In the Tris, according to Needham, two small bees (Clisodon termi- nalis and Osmia distincta) are the most important pollenizers, and next to them a few syrphid flies, while bumble bees also are of some impor- tance. Theoibecwmle Trichius piger and sev- eral small flies obtain pollen without assist- ing the plant, and Pamphila, Eudamus, Chrysophanus and some other butterflies succeed after many trials in stealing the nectar from the out- side (Fig. 260)27 ae weevil (Mononychus vulpeculus) punctures the nectary, and the flowing nectar then at- A, right mandible; B, right maxilla; C, hypo- F . a5 Ss : f pharynx, of a pollen-eating beetle, Euphoria inda. tracts a great variety O Enlarged. (Yhe mandibles are remarkable in insects. Grasshoppers being two-lobed.) 5 and caterpillars eat the flowers, an ortalid fly destroys the buds, and several parasitic or predaceous insects haunt the plant; in all, over sixty species of insects are concerned in one way or another with the J7is. INSECTS IN RELATION TO PLANTS 269 Modifications of Insects with Reference to Flowers.— While the manifold and exquisite adaptations of the flower for cross pollination have engaged universal attention, very little has been recorded concerning the adaptations of insects in re- lation to flowers. In fact, the adapta- tion is largely one-sided; flowers have become adjusted to the structure of in- { sects as a matter of vital necessity—to put it that way—while insects have had no such urgent need—so to speak—in relation to floral structure. They have been influenced by floral structure to some extent, however, and in some cases to a very great extent, as appears from their structural and physiological adapta- tions for gathering and using pollen and ES nectar. Te. 262) Among mandibulate insects, beetles and caterpillars that eat the floral en- Pollen-gathering hair } We : from a worker honey velopess Show no special modifications pee, with a pollen grain io@iunpurpose, pollen-teeding beetles, “see Gray mae: however, usually have the mouth parts densely clothed with hairs, as in Euphoria (Fig. 261). In suctorial insects, the mouth parts are frequently formed with reference to floral structure; this is the case in many but- terflies and particularly in Sphingidz, in which the length of the tongue bears a direct relation to the depth of the nectary in the flowers that they visit. According to Muller, the mouth parts of Syrphide, Stratyomyiide and Muscidz are specially adapted for feeding on pollen. In Apidz, the tongue as com- pared with that of other Hymenoptera, is exceptionally long, enabling the insect to reach deep into a flower, and is exqui- sitely specialized (Fig. 127) for lapping up and sucking in nectar. Pollen-gathering flies and bees collect pollen in the hairs of the body or the legs; these hairs, especially dense and often 270 ENTOMOLOGY twisted or branched (Figs. 262, 89) to hold the pollen, do not occur on other than pollen-gathering species of insects. Cau- dell found that out of 200 species of Hymenoptera only 23 species had branched hairs and that these species belonged without exception to the pollen-gathering group Anthophila, iG 263% Adaptive modifications of the legs of the worker honey bee. A, outer aspect of left hind leg; B, portion of left middle leg; C, inner aspect of tibio-tarsal region of left hind leg; D, tibio-tarsal region of left fore leg; a, antenna comb; b, brush; c, coxa; co, corbiculum; f, femur; pc, pollen combs; s, spur; sp, spines; ss, spines; t, trochanter; fi, tibia; v, velum; w, wax pincers; 7-5, tarsal segments; 7, metatarsus, or planta. no representative of which was found without such hairs. Similar branched hairs occur also on the flower-frequenting Bombylidze and Syrphide. The most extensive modifications in relation to flowers are found in Pronuba, as already described, and above all in Apidze, especially the honey bee. Honey Bee.—The thorax and abdomen and the bases of the legs are clothed with flexible branching hairs (Fig. 262), INSECTS IN RELATION TO PLANTS 2 “J fol which entangle pollen grains. These are combed out of the gathering hairs by means of special pollen combs (Vig. 263, C, pc) on the inner surface of the proximal segment of the hind tarsus, the middle legs also assisting in this operation. From these combs, the pollen is transferred to the pollen baskets, or corbicula (Fig. 263, A, co), of the outer surface of each hind tibia; by crossing the legs, the pollen from one side is trans- ferred to the corbiculum of the opposite side, the spines (ss) on the posterior margin of the tibia serving to scrape the pollen from the combs. Arriving at the nest, the hind legs are thrust into a cell and the mass of pollen on each corbiculum 1s pried out by means of a spur situated at the apex of the middle tibia (Fig. 263, B, s), this lever being slipped in at the upper end of the corbiculum and then pushed along the tibia under the mass of pollen; the spur is used also in cleaning the wings, which explains its presence on queen and drone, as well as worker, but the pollen-gathering structures of the hind legs are confined to the worker. ‘This is true also of the wax- pincers of the hind legs (Fig. 263, A, C, w) at the tibio-tarsal articulation; these nippers are used by the worker to remove the wax plates from the abdomen. For cleaning the antennz, a front leg is passed over an antenna, which slips into a semicircular scraper (Fig. 263, D, a) fashioned from the basal segment of the tarsus; when the leg is bent at the tibio-tarsal articulation, an appendage, or velum (wv), of the tibia falls into place to complete a circular comb, through which the antenna is drawn. This comb is itself cleaned by means of a brush of hairs (b) on the front margin of the tibia. A series of erect spines (sp) along the anterior edge of the metatarsus is used as an eye brush, to remove pollen grains or other foreign bodies from the hairs of the compound eyes. The labium, hypopharynx and max- ile (Fig. 54) are exquisitely constructed with reference to gathering and sucking nectar; the maxillz are used also to smooth the cell walls of the comb; the mandibles (Fig. 45, C), notched in queen and drone but with a sharp entire edge in the ‘ 272 ENTOMOLOGY worker, are used for cutting, scraping and moulding wax, as well as for other purposes. The entire digestive system of the honey bee is adapted in relation to nectar and pollen as food; the proventriculus forms a reservoir for honey and is even provided at its mouth with a rather complex apparatus for straining the honey from the accompanying pollen grains, as described by Cheshire. The wax glands (Fig. 102) are re- markable specializations in correlation with the food habits, as are also the various cephalic glands, the chief functions of which are given as: (1) digestion, as the conversion of cane sugar into grape sugar, and possibly starch into sugar; (2) the chemical alteration of wax; (3) the production of special food substances, which are highly important in larval develop- ment. Numerous special sensory adaptations also occur. In fact, the whole organization of the honey bee has become pro- foundly modified in relation to nectar and pollen. Many other insects have the same food but none of them sustain such intimate relations to the flowers as do the bees. Ant-Plants.—There are several kinds of tropical plants which are admirably suited to the ants that inhabit them. In- deed, it is often asserted that these plants have become modified Fic. 264. Acacia spherocephala, an ant-plant. b, one of the “ Belt’s bodies”; g, gland; s, s, hollow stipular thorns, perforated by ants. Reduced.—From Strasburger’s Lehrbuch der Botantk. INSECTS IN RELATION TO PLANTS 273 with special reference to their use by ants, though this is a gratuitous and improbable assumption. Belt found several species of Acacia in Nicaragua and the Amazon valley which have large hollow stipular thorns, in- habited by ants of the genus Pseudomyrma. ‘The ants enter by boring a hole near the apex of a thorn (Fig. 264, 5). The plant affords the ants food as well as shelter, for glands (g) Fic. 265. Fic. 266. Portion of young stem of Cecropia adenopus, Cecropia adenopus. Por- showing internodal pits, a and b. Natural size. tion of a stem, split so as Figures 265-267 are from Schimper’s Pfanzen- to show internodal cham- geograpiue. bers and the intervening septa perforated by ants. at the bases of the petioles secrete a sugary fluid, while many of the leaflets are tipped with small egg-shaped or pear-shaped appendages (b) known as “ Belt’s bodies,” which are rich in albumin, fall off easily at a touch, and are eaten by the ants. These ants drive away the leaf-cutting species, incidentally protecting the tree in which they live. 19 274 ENTOMOLOGY The ant-trees (Cecropia adenopus) of Brazil and Central America have often been referred to by travelers. When one of these trees is handled roughly, hosts of ants rush out from small openings in the stems and pugnaciously at- tack the disturber. Just above the insertion of each leaf is a small pit (Fig. 265, a, b) where the wall is so thin as to form a mere dia- phragm, through which an ant (probably a fertilized female) bores and reaches a hollow internode. To es- tablish communication —be- tween the internodal cham- bers, the ants bore through the intervening septa (Fig. 266). They seldom leave the Cecropia plant, unless disturbed, and even keep Gecropia adenopus. Base: of peuale showing herds | Of, -apiida as imam “ Miiller’s bodies. Slightly reduced. abode. The base of each petiole bears (Fig. 267) tender little egg-like bodies (“ Mul- ler’s bodies”) which the ants detach, store away and eat; the presence of these bodies is a sure sign that the tree is un- Fic. 267. inhabited by these ants, which, by the way, belong to the genus Azteca. | It is too much to assert that the ants protect the Cecropia plant im return for the food and shelter which they obtain. All ants are hostile to all other species of ants, with few excep- tions, and even to other colonies of their own species; so that their assaults upon leaf-cutting ants are by no means special and adaptive in their nature, and any protection that a plant derives thereby is merely incidental. Furthermore, hollow stems, glandular petioles and pitted stems are of common oc- INSECTS IN RELATION TO PLANTS 275 currence when they bear no relation to the needs of ants. These interrelations of ants and plants are too often misinter- preted in popular and uncritical accounts of the subject. The interesting habits of the leaf-cutting ants in relation to the plants that they attack are described in a subsequent chap- ter, where will be found also an account of the harvesting ants. Fic. 268. Hydnopliyxtum montanum. Section of pseudo-bulb, to show chambers inhabited by ants. One fourth natural size.—After Foret. The epiphytic plants Myrmecodia and Hydnophytum, of Java, form spongy bulb-like masses, the chambers of which are usually tenanted by ants, which rush forth when disturbed. These lumps (Fig. 268) are primarily water-reservoirs, but the ants utilize them by boring into them and from one cham- ber into another. In plants of the genus Humboldtia the ants can enter the hollow internodes through openings that already exist. CREA Bal EARS as INSECTS IN RELATION TO OTHER ANIMALS 1. THE GENERAL SUBJECT On the one hand, insects may derive their food from other animals, either living or dead; on the other hand, insects them- selves are food for other animals, especially fishes and birds, against which they protect themselves by various means, more or less effective. These topics form the principal subject of the present chapter. Predaceous Insects.—Innumerable aquatic insects feed largely or entirely upon microscopic Protozoa, Rotifera, Ento- mostraca, etc.; this is especially the case with culicid and chi- ronomid larve. Many aquatic Hemiptera and Coleoptera prey upon planarians, nematodes, annelids, molluscs and crustaceans; Belostoma sometimes pierces the bodies of tad- poles and small fishes; Dytiscus also kills young fishes occa- sionally and is distinctly carnivorous both as larva and imago. Among terrestrial insects, Carabidze are notably predaceous, preying not only upon other insects but also upon molluscs, myriopods, mites and spiders. Ants do not hesitate to attack all kinds of animals; in the tropics, the wandering ants (Eciton) attack lizards, rats and other vertebrates, and it is said that even huge serpents, when in a torpid condition, are sometimes killed by armies of these pugnacious insects. Mosquitoes affect not only mammals but also, though rarely, fishes and turtles. The gad flies (Tabanide) torment horses and cattle by their punctures; and the black-flies, or buffalo gnats (Simulium), persecute horses, mules, cattle, fowls, and frequently become unendurable even to man. The notorious tsetse fly (Glossina morsitans) of South Africa spreads a deadly disease among horses, cattle and dogs, by 276 INSECTS IN RELATION TO OTHER ANIMALS 27; inoculating them with a protozoan blood-parasite, to the effects of which, fortunately, man is not susceptible. Parasitic Insects.—Insects belonging to several diverse orders have become peculiarly modified to exist as parasites either upon or within the bodies of birds or mammals. Almost all birds are infested by Mallophaga, or bird lice, of which Kellogg has catalogued 264 species from 257 species of North American birds. Sometimes a species of Mallophaga is restricted to a single species of bird, though in the majority of cases this is not so. Several mallophagan species often infest a single bird; thus nine species occur on the hen, and no less than twelve species, representing five genera, on the American coot. These parasites spread by contact from male to female, from old to young, and from one bird to another when the birds are gregarious. When a single species of bird louse occurs on two or more hosts, these are almost always closely allied, and Kellogg has suggested the interesting possibility that such a species has persisted unchanged from a host which was the common ancestor of the two or more present hosts. Mallophaga are not altogether limited to birds, however, for they may be found on cattle, horses, cats, dogs, and some other mammals; Kellogg records eighteen species from fifteen species of mammals. These biting lice feed, not upon blood, but upon epidermal cells and portions of feathers or hairs. They have flat tough bodies (Fig. 17), with no traces of wings, and a large head with only simple eyes; the eggs are glued to feathers or hairs. Mammals only are infested by the sucking lice, or Pediculidze (Hemiptera). These (Fig. 23) have a large oval or rounded abdomen, no wings, a small head, minute simple eyes or none, and claws that are adapted to clutch hairs; the eggs are glued to hairs. Sucking lice affect horses, cattle, sheep, dogs, mon- keys, seals, elephants, etc., and man is parasitized by three species, namely, the head louse (Pediculus capitis), the body louse (Pediculus vestimenti), and the crab louse (Phthirius pubis), though the first two are possibly the same species. 278 ENTOMOLOGY An anomalous beetle, Platypsyllus castoris, occurs through- out North America and also in Europe as a parasite of the beaver. The fleas, allied to Diptera but constituting a distinct order (Siphonaptera), are familiar parasites of chickens, cats, dogs and human beings. These insects (Fig. 30) are well adapted by their laterally compressed bodies for slipping about among hairs, and their saltatory powers and general elusiveness are well known. Their wings are reduced to mere rudiments, their eyes when present are minute and simple and their mouth parts are suctorial. Among Diptera, there are a few external parasites, the best known of which is the sheep tick (Melophagus ovinus), though several highly interesting but little-studied forms are parasitic upon birds and hats. The larvee of the bot flies (Céstridze) are common internal parasites of mammals. The sheep bot fly (CGstrus ovis) deposits her eggs or larve on the nostrils of sheep; the maggots develop in the frontal sinuses of the host, causing vertigo or even death, and when full grown escape through the nostrils and pupate in the soil. The horse bot fly (Gas- trophilus equi) glues its eggs to the hairs of horses, especially on the fore legs and shoulders, whence the larve are licked off and swallowed; once in the stomach, the bots fasten them- selves to its lining, by means of special hooks, and withstand almost all efforts to dislodge them; though when the bots have attained their growth they release their hold and pass with the excrement to the soil. Bots of the genus Hypoderma form tumors on cattle and other mammals, domesticated or wild. The ox-warble (H. lineata, Fig. 210, 1) reaches the cesophagus of its host in the same manner as the horse bot, according to Curtice, but then makes its way into the subcutaneous tissue and causes the well-known tumors on the back of the animal; when full grown the bots squirm cut of these tumors and drop to the ground, leaving permanent holes in the hide. Parasitism in General.—Parasitic insects evidently do not INSECTS IN RELATION TO OTHER ANIMALS 279 constitute a phylogenetic unit, but the parasitic habit has arisen independently in many different orders. These insects do, however, agree superficially, in certain respects, as the result of what may be termed convergence of adaptation. Thus a dipterous larva, living as an internal parasite, in the presence of an abundant supply of food, has no legs, no eyes or anten- ne, and the head is reduced to a mere rudiment, sufficient simply to support a pair of feeble jaws; the skin, moreover, is no longer armor-like but is thin and delicate, the body is com- pact and fleshy, and the digestive system is of a simplified type. The same modifications are found in hymenopterous larve, under similar food-conditions, except that the head usually undergoes less reduction. The various external parasites lack wings, almost invariably, and the eyes, instead of being com- pound, are either simple or else absent. In some special cases, however, as in a few dipterous parasites of birds and bats, the wings are present, either permanently or only temporarily enabling the insects to reach their hosts. This so-called parasitic degeneration, widespread among animals in general and consisting chiefly in the reduction or loss of locomotor and sensory functions in correlation with an immediate and plentiful supply of food, results in a simplicity of organization which is to be regarded—not as a primitive condition—but as an expression of what is, in one sense, a high degree of specialization to peculiar conditions of life. This exquisite degree of adaptation to a special environment, however, sacrifices the general adaptability of the animal,— makes it impossible for a parasite to adapt itself to new con- ditions ; and while parasitism may be an immediate advantage to a species, there are few parasites that have attained any degree of dominance among animals. Ichneumonidz, to be sure, are remarkably dominant among insects, but here the parasitic adaptations are limited for the most part to the larval stage and the adults may be said to be as free for new adapta- tions as are any other Hymenoptera. Scavenger and Carrion Insects.—Not a few families of 280 ENTOMOLOGY Diptera and Coleoptera derive their food from dead animal matter. The aquatic families Dytiscidze and Gyrinide are largely scavengers. Among terrestrial forms, Silphidz feed on dead animals of all kinds; the burying beetles (Necroph- orus), working 1n pairs, undermine and bury the bodies of birds, frogs and other small animals, and lay their eggs in the carcasses; Histeridze and Staphylinide are carrion beetles, and Dermestidz attack dried animal matter of almost every de- scription, their depredations upon furs, feathers, museum specimens, etc., being familiar to all. Ants are famous as scavengers, destroying decaying organic matter in immense quantities, particularly in the tropics. Many Scarabzeidz feed upon excrementitious matter, for example the “ tumble-bugs,” which are frequently seen in pairs, laboriously rolling along or burying a large ball of dung, which is to serve as food for the larva. : Insects as Food for Vertebrates.—Lizards, frogs and toads are insectivorous, especially toads. The American toad feeds chiefly upon insects, which form 77 per cent. of its food for the season, the remainder consisting of myriopods, spiders, crustacea, molluscs and worms, according to the observations of A. H. Kirkland, who states that Lepidoptera form 28 per cent. of the total insect food, Coleoptera 27, Hymenoptera 19 and Orthoptera 3 per cent. The toad does not capture dead or motionless insects but uses its extensile sticky tongue to lick in moving insects or other prey, which it captures with sur- prising speed and precision. In the cities one often sees many toads under an arc-light engaged in catching insects that fall anywhere near them. ‘Though its diet is varied and some- what indiscriminate, the toad consumes such a large propor- tion of noxious insects, such as May beetles and cutworms, that it is unquestionably of service to man. Moles are entirely insectivorous and destroy large numbers of white grubs and caterpillars; field mice and prairie squirrels eat many insects, especially grasshoppers, and the skunk rey- els in these insects, though it eats beetles frequently, as does INSECTS IN RELATION TO OTHER ANIMALS 281 also the raccoon, which is to some extent insectivorous. Monkeys are omnivorous but devour many kinds of insects. With these hasty references, we may pass at once to the subject of the insect food of fishes and birds. Insects in Relation to Fishes.—Insects constitute the most important portion of the food of adult fresh water fishes, furnishing forty per cent. of their food, according to Dr. Forbes, from whose valuable writings the following extracts are taken. “The principal insectivorous fishes are the smaller species, whose size and food structures, when adult, unfit them for the capture of Entomostraca, and yet do not bring them within reach of fishes or Mollusca. Some of these fishes have pecu- liar habits which render them especially dependent upon insect life, the little minnow Phenacobius, for example, which, ac- cording to my studies, makes nearly all its food from insects (ninety-eight per cent.) found under stones in running water. Next are the pirate perch, Aphredoderus (ninety-one per cent.), then the darters (eighty-seven per cent.), the croppies (seventy-three per cent.), half-grown sheepshead (seventy- one per cent.), the shovel fish (fifty-nine per cent.), the chub minnow (fifty-six per cent.), the black warrior sunfish (Cheno- bryttus) and the brook silversides (each fifty-four per cent.), and the rock bass and the cyprinoid genus Notropis (each fifty-two per cent.). “Those which take few insects or none are mostly the mud- feeders and the ichthyophagous species, Amia (the dog-fish) being the only exception noted to this general statement. Thus we find insects wholly or, nearly absent from the adult dietary of the burbot, the pike, the gar, the black bass, the wall- eyed pike, and the great river catfish, and from that of the hickory shad and the mud-eating minnows (the shiner, the fat- head, etc.). It is to be noted, however, that the larger fishes all go through an insectivorous stage, whether their food when adult be almost wholly other fishes, as with the gar and the pike, or molluscs, as with the sheepshead. The mud- 282 ENTOMOLOGY feeders, however, seem not to pass through this stage, but to adopt the limophagous habit as soon as they cease to depend upon Entomostraca. ‘Terrestrial insects, dropping into the water accidentally or swept in by rains, are evidently diligently sought and largely depended upon by several species, such as the pirate perch, the brook minnow, the top minnows or _ killifishes (cyprinodonts), the toothed herring and several cyprinoids (Semotilus, Pimephales and Notropis). Among aquatic insects, minute slender dipterous larvee, belonging mostly to Chironomus, Corethra and allied genera. are of remarkable importance, making, in fact, nearly one tenth of the food of all the fishes studied. They are most abundant in Phenacobius and Etheostoma, which genera have become especially adapted to the search for these insect forms in shallow rocky streams. Next I found them most generally in the pirate perch, the brook silversides, and the stickleback, in which they averaged forty-five per cent. They amounted to about one third the food of fishes as large and important as the red horse and the river carp, and made nearly one fourth that of fifty-one buffalo fishes. They appear further in con- siderable quantity in the food of a number of the minnow family (Notropis, Pimephales, etc.), which habitually fre- quent the swift waters of stony streams, but were curiously deficient in the small collection of miller’s thumbs (Cottidz) which hunt for food in similar situations. The sunfishes eat but few of this important group, the average of the family being only six per cent. “ Larve of aquatic beetles, notwithstanding the abundance of some of the forms, occurred in only insignificant ratios, but were taken by fifty-six specimens, belonging to nineteen of the species,—more frequently by the sunfishes than by any other group. The kinds most commonly captured were larve of Gyrinidz and Hydrophilidz ; whereas the adult surface beetles themselves (Gyrinus, Dineutes, etc.)—whose zigzag-darting swarms no one can have failed to notice—were not once en- countered in my studies. INSECTS IN RELATION TO OTHER ANIMALS 283 “The almost equally well-known slender water-skippers (Hygrotrechus) seem also completely protected by their habits and activity from capture by fishes, only a single specimen oc- curring in the food of all my specimens. Indeed, the true water bugs (Hemiptera) were generally rare, with the excep- tion of the small soft-bodied genus Corisa, which was taken by one hundred and ten specimens, belonging to twenty-seven species,—most abundantly by the sunfishes and top minnows. “From the order Neuroptera [in the broad sense] fishes draw a larger part of their food than from any other single group. In fact, nearly a fifth of the entire amount of food consumed by all the adult fishes examined by me consisted of aquatic larve of this order, the greater part of them larvze of day flies (Ephemeridz), principally of the genus Hevagenia. These neuropterous larve were eaten especially by the miller’s thumb, the sheepshead, the white and striped bass, the common perch, thirteen species of the darters, both the black bass, seven of the sunfishes, the rock bass and the croppies, the pirate perch, the brook silversides, the sticklebacks, the mud minnow, the top minnows, the gizzard shad, the toothed herring, twelve species each of the true minnow family and of the suckers and buffalo, five catfishes, the dog-fish, and the shovel fish,— seventy species out of the eighty-seven which | have studied. “Among the above, I found them the most important food of the white bass, the toothed herring, the shovel fish (fifty- one per cent.), and the croppies; while they made a fourth or more of the alimentary contents of the sheepshead (forty-six per cent.), the darters, the pirate perch, the common sunfishes (Lepomis and Chenobryttus), the rock bass, the little pickerel., and the common sucker (thirty-six per cent. ). “ Ephemerid larve were eaten by two hundred and thirteen specimens of forty-eight species—not counting young. The larve of Hexagenia, one of the commonest of the ‘ river flies, was by far the most important insect of this group, this alone amounting to about half of all the Neuroptera eaten. ‘They made nearly one half of the food of the shovel fish, more 284 ENTOMOLOGY than one tenth that of the sunfishes, and the principal food re- sources of half-grown sheepshead; but were rarely taken by the sucker family, and made only five per cent. of the food of the catfish group. “The various larve of the dragon flies, on the other hand, were much less frequently encountered. They seemed to be most abundant in the food of the grass pickerel (twenty-five per cent.), and next to that, in the croppie, the pirate perch, and the common perch (ten to thirteen per cent.). “Case-worms (Phryganeide) were somewhat rarely found, rising to fifteen per cent. in the rock bass and twelve per cent. in the minnows of the Hybopsis group, but otherwise averaging from one to six per cent. in less than half of the Species: « Insects in Relation to Birds.—From an economic point of view the relations between birds and insects are extremely important, and from a purely scientific standpoint they are no less important, involving as they do biological interactions of remarkable complexity. The prevalent popular opinion that birds in general are of inestimable value as destroyers of noxious insects is a correct one, as Dr. Forbes proved, from his precise and extensive studies upon the food of Illinois birds, involving a laborious and difficult examination of the stomach contents of many hundred specimens. All that follows is taken from Forbes, when no other author’s name is mentioned, and though the percentages given by Forbes apply to particular years and would undoubtedly vary more or less from year to year, they are here for convenience regarded as representative of any year and are spoken of in the present tense. About two thirds of the food of birds consists of insects. Robin.—The food of the robin in Illinois, from February to May inclusive, consists almost entirely of insects; at first, larvee of Bibio albipennis for the most part, and then caterpil- lars and various beetles. When the small fruits appear, these are largely eaten instead of insects; thus in June, cherries and INSECTS IN RELATION TO OTHER ANIMALS 285 raspberries form fifty-five per cent. and insects (ants, cater- pillars, wire-worms and Carabide) forty-two per cent. of the food; and in July, raspberries, blackberries and currants form seventy-nine per cent. and insects (mostly caterpillars, beetles and crickets) but twenty per cent. of the food. In August, insects rise to forty-three per cent. and fruits drop to fifty-six per cent., and these are mostly cherries, of which two thirds are wild kinds. In September, ants form fifteen per cent. of the food, caterpillars five per cent. and fruits (mostly grapes, mountain-ash berries and moonseed berries) seventy per cent. In October, the food consists chiefly of wild grapes (fifty- three per cent.), ants (thirty-five per cent.), and caterpillars (Sic percent, )'. For the year, judging from the stomach contents of one hundred and fourteen birds, garden fruits form only twenty- nine per cent. of the food of the robin, while insects constitute two thirds of the food. The results are confirmed by those of Professor Beal in Michigan, who found that more than forty-two per cent. of the food of the robin consists of insects with some other animal matter, the remainder being made up of various small fruits, but notably the wild kinds. Upon the whole, the robin deserves to be protected as an energetic destroyer of cutworms, white grubs and other injuri- ous insects, and the comparatively few cultivated berries that the bird appropriates are ordinarily but a meagre compensa- tion for the valuable services rendered to man by this familiar bird. Catbird.—Not so much can be said for the catbird, however, for though its food habits are similar to those of the robin, it arrives later and departs earlier, with the result that it is less dependent than the robin upon insects and that berries form a larger percentage of its total food. In May, eighty-three per cent. of the food of the catbird consists of insects, mostly beetles (Carabidze, Rhynchophora, etc.), crane-flies, ants and caterpillars (Noctuide) ; while dry sumach berries are eaten to the extent of seven per cent. For 286 ENTOMOLOGY the first half of June, the record is much the same, with an in- crease, however, in the number of May beetles eaten; in the second half of the month, the food consists chiefly of small fruits, especially raspberries, cherrtes and currants; so that for the month as a whole, only forty-nine per cent. of the food is made up of insects. This falls to eighteen per cent. in July, when three quarters cf the food consists of small fruits, mostly blackberries, however. In August, with the diminu- tion of the smaller cultivated fruits, the percentage of insects rises to forty-six per cent., nearly one half of which is made up of ants and the rest of caterpillars, grasshoppers, Hemip- tera, Coleoptera, etc. In September, with the appearance of wild cherries, elderberries, Virginia creeper berries and grapes, these are eaten to the extent of seventy-six per cent., the insect element of the food falling to twenty-one per cent., of which almost half consists of ants, and the remainder of beetles and a few caterpillars. For the entire year, as appears from the study of seventy specimens by Forbes, insects form forty-three per cent. of the food of the catbird and fruits fifty-two per cent. As the in- jurious insects killed are offset by the beneficial ones destroyed, “the injury done in the fruit-garden by these birds remains without compensation unless we shall find it in the food of the young,” says Professor Forbes. And this has been found, to the credit of the catbird; for Weed learned that the food of three nestlings consisted of insects, sixty-two per cent. of which were cutworms and four per cent. grasshoppers; while Judd found that fourteen nestlings had eaten but four per cent. of fruit, the diet being chiefly ants, beetles, caterpillars, spiders and grasshoppers. In fact, Weed believes that, on the whole, the benefit received from the catbird is much greater than the harm done, and that its destruction should never be permitted except when necessary in order to save precious crops. Bluebird.—The excellent reputation which the bluebird bears everywhere as an enemy of noxious insects is well-de- INSECTS IN RELATION TO OTHER ANIMALS 28.7 served. From a study of one hundred and eight Illinois speci- mens, Forbes finds that seventy-eight per cent. of the food for the year consists of insects, eight per cent. of Arachnida, one per cent. of Julidze and only thirteen per cent. of vegetable matter, edible fruits forming merely one per cent. of the entire food. The insects eaten are mostly caterpillars (chiefly cut- worms), Orthoptera (grasshoppers and crickets) and Cole- optera (Carabide and Scarabzide). Though some of the insects are more or less beneficial to man, such as Carabidz and Ichneumonidz (respectively predaceous and_ parasitic), the beneficial elements form only twenty-two per cent. of the food for the year, as against forty-nine per cent. of injurious elements, the remaining twenty-nine per cent. consisting of neutral elements. The food of the nestlings, according to Judd, is essentially like that of the adults, being “ beetles, caterpillars, grasshoppers, spiders and a few snails.”’ Other Insectivorous Birds.—Weed and Dearborn, from whose excellent work the following notes are taken, find that the common chickadee devours immense numbers of canker- worms, and that more than half its food during winter con- sists of insects, largely in the form of eggs, including those of the common tent caterpillar (C. americana), the fall web- worm (H. cunea) and particularly plant lice, whose eggs, small as they are, form more than one fifth of the entire food; more than four hundred and fifty of them are sometimes eaten by a single bird in one day, and the total number destroyed annually is inconceivably large. The house wren is almost exclusively insectivorous, feeding upon caterpillars and other .larvee, ants, grasshoppers, gnats, beetles, bugs, spiders, and myriopods. The swallows, also, are highly insectivorous; “most of their food is captured on the wing, and consists of small moths, two-winged flies, especially crane-flies, beetles in great variety, flying bugs, and occasionally small dragon-flies. The young are fed with insects.” Ninety per cent. of the food of the kingbird “consists of insects, including such noxious species as May-beetles, click-beetles, wheat and fruit weevils, 288 ENTOMOLOGY grasshoppers, and leafhoppers.” The honey bees eaten by this bird are insignificant in number. Woodpeckers destroy immense numbers of wood-boring larvee, bark-insects, ants, caterpillars, etc. The cuckoos “are unique in having a taste for insects that other birds reject. Most birds are ready to devour a smooth caterpillar that comes in their way, but they leave the hairy varieties severely alone. The cuckoos, how- ever, make a specialty of devouring such unpalatable crea- tures; even stink-bugs and the poisonous spiny larvze of the lo moth are freely taken.” Caterpillars form fifty per cent. of the food for the year; Orthoptera (grasshoppers, katydids, and tree crickets), thirty per cent. ; Coleoptera and Hemiptera, six per cent. each; and flies and ants are taken in small quanti- ties. ‘‘ The nestling birds are fed chiefly with smooth cater- pillars and grasshoppers, their stomachs probably being unable to endure the hairy caterpillars. All in all, the cuckoos are of the highest economic value. They do no harm and accom- plish great good. If the orchardist could colonize his or- chards with them, he would escape much loss.” The quail feeds largely upon insects during the summer, frequently eat- ing the Colorado potato beetle and the army worm; the prairie hen has similar food habits but lives almost exclusively on grasshoppers, when these are abundant. The Insect Food of Birds.—‘‘ There are few groups of injurious insects that enter so largely into the composition of the food of birds as do the locusts, or short-horned grasshop- pers, of the family Acridiide. The enormous destructive power of these insects is well known, but our indebtedness to birds in checking their oscillations is less generally recog-, nized.” Professor Aughey, who has made extensive studies upon the relation of birds to the Rocky Mountain locust, found that upon one occasion 6 robins had eaten 265 of these insects, 5 catbirds 152, 3 bluebirds 67, 7 barn swallows 139, 7 night hawks 348, 16 yellow-billed cuckoos 416, 8 flickers 252, 8 screech owls 219, and 1 humming bird 4; while crows and blue-jays had eaten large numbers of the locusts; and grouse, INSECTS IN RELATION TO OTHER ANIMALS 289 quail and prairie hen, enormous numbers. Even shore birds, such as geese, ducks, gulls and pelicans came to share in the feast. Aughey estimated that the locusts eaten in one day by the passerine birds of the eastern half of Nebraska were sufficient to destroy in a single day 174.397 tons of crops, valued at $1,743.97. Weed and Dearborn state that, of Hemiptera, Jasside are very often found in the stomachs of birds, and that aphids and their eggs form a large part of the food of many of the smaller birds, such as the warblers, nuthatches, kinglets and chickadees. “ A large proportion of the caterpillars of the Lepidoptera are eagerly devoured by birds, forming an important element of the food of many species.”’ The hairy caterpillars are eaten by cuckoos and blue-jays and the large saturniid caterpillars, such as cecropia and polyphemus, by some of the hawks. AI- most all kinds of Coleoptera are food for birds, but especially the grubs of Scarabzidz, which are eagerly devoured by robins, blackbirds, crows and other birds. Of the Diptera, Cecidomyiidz and other gnats are eaten by swallows, swifts and night hawks; while Tipulidz are often found in the stom- achs of birds. Among Hymenoptera, ants are eaten exten- sively by woodpeckers, catbirds and many other species, as are also Ichneumonide and other parasitic forms—these last by the flycatchers in particular. The Regulative Action of Birds upon Insect Oscilla- tions.—The worst injuries by insects are done by species that fluctuate excessively in number as the result of variations in those manifold forces that act as checks upon the multiplica- tion of the species. In order to determine whether birds do anything to reduce existing oscillations of injurious insects, Professor Forbes made some admirable studies upon the food of birds which were shot in an Illinois apple orchard which was being ravaged by canker-worms. In this orchard, birds were present in extraordinary number and variety, there being at least thirty- five species, most of which were studied by Forbes, from 20 290 ENTOMOLOGY whose exhaustive tables the following food-percentages are taken : Birds Examined. Insects. Canker-worms. Robin, 9 03 4 Bey, Catbird, I4 98 15 Brown Thrush, 4 O4 12 Bluebird, 5 98 12 Black-capped Chickadee, 2 100 61 House Wren, 5 OI 46 Tennessee Warbler, I 100 80 Summer Yellow Bird, 5 04 67 Black-throated Green Warbler, 1 100 70 Maryland Yellow-throat, 2 100 37 Baltimore Oriole, R 100 40 To quote Forbes: “ Three facts stand out very clearly as results of these investigations: 1. Birds of the most varied character and habits, migrant and resident, of all sizes, from the tiny wren to the blue-jay, birds of the forest, garden and meadow, those of arboreal and those of terrestrial habits, were certainly either attracted or detained here by the bountiful supply of insect food, and were feeding freely upon the species most abundant. That thirty-five per cent. of the food of all the birds congregated in this orchard should have consisted of a single species of insect, is a fact so extraordinary that its meaning can not be mistaken. Whatever power the birds of this vicinity possessed as checks upon destructive irruptions of insect life, was being largely exerted here to restore the broken balance of organic nature. And while looking for their in- fluence over one insect outbreak we stumbled upon at least two others, less marked, perhaps incipient, but evident enough to express themselves clearly in the changed food ratios of the birds. “9. The comparisons made show plainly that the reflex effect of this concentration on two or three unusually numerous in- sects was so widely distributed over the ordinary elements of their food that no especial chance was given for the rise of new fluctuations among the species commonly eaten. That is to say, the abnormal pressure put upon the canker-worm and vine- INSECTS IN RELATION TO OTHER ANIMALS 291 chafer was compensated by a general diminution of the ratios of all the other elements, and not by a neglect of one or two alone. If the latter had been the case, the criticism might easily have been made that the birds, in helping to reduce one oscillation, were setting others on foot. “3. The fact that, with the exception of the indigo bird, the species whose records in the orchard were compared with those made elsewhere, had eaten in the former situation as many caterpillars other than canker-worms as usual, simply adding their canker-worm ratios to those of other caterpillars, goes to show that these insects are favorites with a majority of birds.”’ The Relations of Birds to Predaceous and Parasitic In- sects.—The false assumption is often made that a bird is necessarily inimical to man’s interest whenever it destroys a parasitic or a predaceous insect. Weed and Dearborn attack this assumption as follows: ‘“* Suppose an ichneumon parasite is found in the stomach of a robin or other bird: it may belong to any one of the follow- ing categories : “1. The primary parasite of an injurious insect. ‘““2. The secondary parasite of an injurious insect. “3. The primary parasite of an insect feeding on a noxious plant. “4. The secondary parasite of an insect feeding on a nox- ious plant. “5. The primary parasite of an insect feeding on a wild plant of no economic value. “6. The secondary parasite of an insect feeding on a wild plant of no economic value. “7. The primary parasite of a predaceous insect. “8. The primary parasite of a spider or a spider’s egg. “This list might easily be extended still farther, and the assumption that the parasite belongs to the first of these cate- gories is unwarranted by the facts and does violence to the probabilities of the case. 292 ENTOMOLOGY * A correct idea of the economic role of the feathered tribes may be obtained only by a broader view of nature’s methods, a view in which we must ever keep before the mind’s eye the fact that all the parts of the organic world, from monad to man, are linked together in a thousand ways, the net result being that unstable equilibrium commonly called * the balance of nature” * This broader view was first elaborated by Professor Forbes, in his masterly paper, “On Some Interactions of Organisms,” the substance of which is given below. “Evidently a species can not long maintain itself in num- bers greater than can find sufficient food, year after year. If it is a phytophagous insect, for example, it will soon dwindle if it seriously lessens the numbers of the plants upon which it feeds, either directly, by eating them up, or indirectly, by so weakening them that they labor under a,marked disadvantage in the struggle with other plants for foothold, air, light and food. The interest of the insect is therefore identical with the interest of the plant it feeds upon. Whatever injuriously affects the latter, equally injures the former; and whatever favors the latter, equally favors the former. This must, therefore, be regarded as the extreme normal limit of the num- bers of a phytophagous species, a limit such that its depre- dations shall do no especial harm to the plants upon which it depends for food, but shall remove only the excess of foliage or fruit, or else superfluous individuals which must perish otherwise, if not eaten, or, surviving, must injure their species’ by over-crowding. If the plant-feeder multiply beyond the above limit, evidently the diminution of its food supply will soon react to diminish its own numbers; a counter reaction will then take place in favor of the plant, and so on through an oscillation of indefinite continuance. “On the other hand, the reduction of the phytophagous in- sect below the normal number, will evidently injure the food plant by preventing a reduction of its excess of growth or numbers, and will also set up an oscillation like the preceding, except that the steps will be taken in reverse order. INSECTS IN RELATION TO OTHER ANIMALS 293 “T next point out the fact that precisely the same reasoning applies to predaceous and parasitic insects. Their interests, also are identical with the interests of the species they para- sitize or prey upon. a oe Pee od ; re >. 1g, 7 . a bd ny ‘ o ‘ke , ‘ i f DISTRIBUTION BV, ‘ The Austral region “ covers the whole of the United States and Mexico, except the Boreal mountains and the Tropical lowlands.”” It comprises three transcontinental belts: (1) the Transition zone, in which the Boreal and the Austral overlap; (2) the Upper Austral; (3) the Lower Austral. The butter- Distribution of Erynnis manitoba, a Distribution in the United States of butterfly restricted to subarctic and sub- Eudamus proteus, primarily a_ tropical alpine regions.—After SCUDDER. butterfly.—After SCUDDER. fly Eudamus proteus (Fig. 293) 1s restricted, generally speak- ing, to the Tropical region and the warmer and more humid portions of the Austral. The Tropical region covers the southern extremity of Florida and of Lower California, most of Central America and a narrow strip along the two coasts of Mexico, the western strip extending up into California and Arizona. These divisions are based primarily upon the distribution of mammals, birds and plants, and the three primary divisions serve almost equally well for insects also. In regard to the zones, however, not so much can be said—for insects are to a high degree independent of minor differences of climate. Many instances of this are given beyond. The insect fauna of the United States is upon the whole a heterogeneous assemblage of species derived from several sources, and the foreign element of this fauna we shall con- sider at some length. Paths of Diffusion in North America.—It may be laid down as a general rule that every species tends to spread in 378 ENTOMOLOGY all directions and does so spread until its further progress is prevented, in one way or another. The paths along which a species spreads are determined, then, by the absence of barri- ers. The diffusion of insects in our own country has received much attention from entomologists, especially in the case of such insects as are important from an economic standpoint. The accessions to our insect fauna have arrived chiefly from Asia, Central and South America, and Europe. Webster, our foremost student of this subject, to whom the author is indebted for most of his facts, names four paths along which insects have made their way into the United States: (1) Northwest—Northern Asia into Alaska and thence south and east; (2) Souwthwest—Central America through Mexico; (3) Southeast—West Indies into Florida; (4) Eastern—from Europe, commercially. Northwest. — The northern parts of Europe, Asia and North America have in common very many identical or closely allied species, whose distribution is accounted for if, as geol- ogists assure us, Asia and North America were once con- nected, at a time when a subtropical climate prevailed within the Arctic Circle; in fact, the distribution is scarcely explic- able upon any other theory. Curiously enough, the trend of diffusion seems to have been from Asia into North America and rarely the reverse, so far as can be inferred. Coccinella quinquenotata, occurring in Siberia and Alaska, has spread to Hudson Bay, Greenland, Kansas, Utah, Califor- nia and Mexico; while C. sanguinea, well known in Europe and Asia, ranges from Alaska to Patagonia; and Megilla mac- ulata from Vancouver and Canada to Chile. About six hun- dred species of beetles are holarctic in distribution, as was mentioned. Some of them inhabit different climatal regions in different parts of their range; thus Melasoma (Lina) lap- ponica in the Old World “ occurs only in the high north and on high mountain ranges, whereas in North America it ex- tends to the extreme southern portion of the country,” being widely diffused over the lowlands (Schwarz). Similarly, DISTRIBUTION 379 Silpha lapponica is strictly arctic in Europe, but is distributed over most of North America; Silpha opaca, on the contrary, is common all over Europe, but is strictly arctic in North America. Silpha atrata, common throughout Europe and western Siberia, was introduced into North America, but failed to establish itself. Southwest.— Very many species have come to us from Cen- tral America and even from South America. South America appears to be the home of the genus Halisidota, according to Webster, who has traced several of our North American spe- cies as offshoots of South American forms. Many of our species may be traced back to Yucatan. H. cinctipes ranges from South America to Texas and Florida; H. tessellaris has spread northward from Central America and now occurs over the middle and eastern United States, while a form closely like tessellaris ranges from Argentina to Costa Rica; H. carye follows tessellaris, and appears to have branched in Central America, giving off H. agassizu, which extends northward into California. Similarly in the case of the Colorado potato beetle (Leptinotarsa decemlineata) and its relatives. Accord- ing to Tower, the parent form, L. undecemlineata, seems to have arisen in the northern part of South America, to have migrated northward and, in the diversified Mexican region, to have split into several racial varieties. The parent form erades into L. multilineata of the Mexican table lands, which in turn, in the northern part of the Mexican plateau, passes imperceptibly into L. decemlineata, which last species has spread northward along the eastern slope of the western high- lands, west of the arid region. In the lower part of the Mex- ican region the parent form may be traced into L. juncta, which has spread along the low humid Gulf Coast, up the Miss- issippi valley to southern Ilinois, and along the Gulf Coast and up the Atlantic coast to Maryland, Delaware and New Jersey. In general, the mountains of Central America and Mexico and the plateau of Mexico have been barriers to the northward spread of many species, which have reached the 380 ENTOMOLOGY United States by passing to the east or to the west of these barriers, in the former case skirting the Gulf of Mexico and spreading northward along the Mississippi valley or along the Atlantic coast, in the latter event traveling along the Pacific coast to California and other Western states. Not a few spe- cies, however, have made their way from the Mexican plateau into New Mexico and Arizona; this is true of many Sphin- gide. The butterfly Anosia berenice ranges from South America into New Mexico, Arizona and Colorado; while many of the Libytheidz have entered Arizona and neighboring states from Mexico. The chrysomelid genus Diabrotica is almost exclusively confined to the western hemisphere and its home is clearly in South America, where no less than 367 species are found. About 100 species occur in Venezuela and Colombia, “of which It extend into Guatemala, 8 into Mexico, and 1 into the United States.”’ We have 18 species of Diabrotica, almost all of which can be traced back to Mexico, and several of them—as the common D. longicornis—to Central America. “The common Dynastes tityus occurs from Brazil through Central America and Mexico, and in the United States from Texas to Illinois and east to southern New York and New England.” Erebus odora ranges from Ecuador and Brazil to Colorado, Illinois, Ohio, New England and into Canada, though it is not known to breed in North America, being in fact a rare visitor in our northern states. Southeast.—Many South American species have made their way into southern and western Florida by way of the West Indies, while some subtropical species have reached Florida probably by following around the Gulf coast. The semi- tropical insect fauna of southern and southwestern Florida, including about 300 specimens of Coleoptera, according to Schwarz, is entirely of West Indian and Central American origin, the species having been introduced with their food plants, chiefly by the Gulf Stream, but also by flight, as in the case of Sphingide. Ninety-five speciesof Hemiptera collected in extreme southern Florida by Schwarz and studied by Uhler DISTRIBUTION 381 are distinctly Central American and West Indian in their affinities. Indeed Uhler is inclined to believe that the principal portion of the Hemiptera of the United States has been derived from the region of Central America and Mexico. Eastern.—On the Atlantic coast are many European species of insects which have arrived through the agency of man. Most of them have not as yet passed the Appalachian moun- tain system, but some have worked their way inland. Thus the common cabbage butterfly (Pieris rape), first noticed in Quebec about 1860, was found in the northern parts of Maine, New Hampshire and Vermont five or six years later, was established in those states by 1867, entered New York in 1868 and then Ohio. Aphodius fossor followed much the same course from New York into northeastern Ohio, as did also the asparagus beetle (Crioceris asparagi), the clover leaf weevil (Phytonomus punctatus), the clover root borer (Hylastes obscurus) and other species. In short, as Webster has pointed out, New York offers a natural gateway through which species introduced from Europe spread westward, passing either to the north or to the south of Lake Erie. Inland Distribution.—Picris rape, the spread of which in North America has been thoroughly traced by Scudder, reached northern New York in 1868 (as above), but appears to have been independently introduced into New Jersey in 1868, whence it reached eastern New York again in 1870; it was seen in northeastern Ohio in 1873, Chicago 1875, lowa 1878, Minnesota 1880, Colorado 1886, and has extended as far south as northern Florida, but is apparently unable to make its way down into the peninsula. Crioceris asparagi, another native of Europe, became con- spicuous in Long Island in 1856, spread southward to Virginia and westward to Ohio, where it was taken in 1886; it occurs now in Illinois. This insect, as Howard observes, flies read- ily, and may be introduced commercially in the egg or larval stage on bunches of asparagus. Cryptorhynchus lapathi, a beetle destructive to willows and 382 ENTOMOLOGY poplars, and common in Europe, Siberia and Japan, was found in New Jersey in 1882 and in New York in 1896, though known for many years previously in Massachusetts. It be- came noticeable in Ohio in 1901, and is steadily extending its ravages, being reported recently from Minnesota. From Colorado the well-known potato beetle (Leptinotarsa decemlineata) has worked eastward since 1840, reaching the Atlantic coast within twenty years, and has even made its way several times into Great Britain, only to be stamped out with commendable energy. The box-elder bug (Leptocoris trivit- tatus) is similarly working eastward, having now reached Indiana. The Rocky Mountain locust periodically migrates eastward, but meets a check in the moist valley of the Missis- sippi, as has been said. The chinch bug (Blissus leucopterus), the distribution of which has been traced by Webster, has spread from Central America and Mexico northward along the Gulf coast into the United States, following three paths: (1) Along the Atlantic coast to Cape Breton; (2) along the Mississippi valley and northward into Manitoba; (3) along the western coast of Cen- tral America and Mexico into California and other Western states. Everywhere this insect has found wild grasses upon which to feed, but has readily forsaken these for cultivated grasses upon occasion. The harlequin cabbage bug (Murgan- tia histrionica) has spread from Central America into Califor- nia and Nevada, and has steadily progressed in the Mississippi basin as far north as Illinois, Indiana and Ohio, though it appears to be unable to maintain itself in the northern parts of these states. This insect required about twenty-five years to pass from Louisiana (1864) to Ohio, spreading through its own efforts and not commercially to any great extent. Every year some of the southern butterflies reach the North- ern states, where they die without finding a food plant, or else maintain a precarious existence. Thus [phiclides ajax occa- sionally reaches Massachusetts as a visitor and a visitor only; Lertias philenor, however, finds a limited amount of food in DISTRIBUTION 383 the cultivated Aristolochia. P. thoas, one of the pests of the orange tree in the South, is highly prized as a rarity by New England collectors and is able to perpetuate itself in the Middle States on the prickly ash (Xanthorylum). The strong-winged grasshopper, Schistocerca americana, belonging to a genus the center of whose dispersion is tropical America, ranges freely over the interior of North America, sometimes in great swarms, and its nymphs are able to survive in mode- rate numbers in the southern parts of Illinois, Ohio and other states of as high latitude, while the adults occasionally reach Ontario, Canada. Many species are now so widely distributed that their for- mer paths of diffusion can no longer be ascertained. The army worm (FHeliophila unipuncta), feeding on grasses, and occurring all over the United States south of Lat. 44° N., is found also in Central America, throughout South America, and in Europe, Africa, Japan, China, India, etc.; in short, it occurs in all except the coldest parts of the earth, and where it originated no one knows. Determination of Centers of Dispersal.—In accounting for the present distribution of life, naturalists employ several kinds of evidence. Adams recognizes ten criteria, aside from paleontological evidence, for determining centers of dispersal: 1. Location of greatest differentiation of a type. 2. Location of dominance or great abundance of individuals. 3. Location of synthetic or closely related forms (Allen). 4. Location of maximum size of individuals (Ridgway- Allen). 5. Location of greatest productiveness and its relative sta- bility, in crops (Hyde). 6. Continuity and convergence of lines of dispersal. 7. Location of least dependence upon a restricted habitat. 8. Continuity and directness of individual variations or - modifications radiating from the center of origin along the highways of dispersal. g. Direction indicated by biogeographical affinities. 384 ENTOMOLOGY vy 10. Direction indicated by the annual migration routes, in birds (Palmén). 2. GEOLOGICAL Means of Fossilization.—Abundant as insects are at pres- ent, they are comparatively rare as fossils, the fossil species forming but one per cent. of the total number of described species of insects. The absence of insect remains in sedimen- tary rocks of marine origin is explained by the fact that almost no insects inhabit salt water; and terrestrial forms in general are ill-adapted for fossilization. The hosts of insects that die each year leave remarkably few traces in the soil, owing per- haps, in great measure, to the dissolution of chitin in the pres- ence of moisture. Most of the fossil insects that are known have been found in vegetable accumulations such as coal, peat and lhegnite, or else in ancient fresh-water basins, where the insects were prob- ably drowned and rapidly imbedded. At present, enormous numbers of insects are sometimes cast upon the shores of our great lakes—a phenomenon which helps to explain the profu- sion of fossil forms found in some of the ancient lake basins. Insects in rich variety have been preserved in amber, the fossilized resin of coniferous trees. This substance, as it exuded, must have entangled and enveloped insect visitors just as it does at present. Many of these amber insects are ex- quisitely preserved, as if sealed in glass. Copal, a transparent, amber-like resin from various tropical trees, particularly Legu- minosze, has also yielded many interesting insects. Ill-adapted as insects are by organization and habit for the commoner methods of fossilization, the number of fossil spe- cies already described is no less than three thousand. Localities for Fossil Insects.—The Devonian of New Brunswick has furnished a few forms, found near St. John, in a small ledge that outcrops between tide-marks; these forms, though few, are of extraordinary interest, as will be seen. For Carboniferous species, Commentry in France is a noted locality, through the admirable researches of Brongniart, who DISTRIBUTION 385 described from there 97 species of 48 genera, representing 12 families or higher groups, 10 of which are regarded as extinct; without including many hundred specimens of cockroaches which he found but did not study. In this country, many species have been found in the coal fields of Illinois, Nova Scotia, Rhode Island, Pennsylvania and Ohio. Many fine fossils of the Jurassic period have been found in the lithographic limestones of Bavaria; 143 species from the Lias-—four fifths of them beetles—were studied by Heer. The Tertiary period has furnished the majority of fossil specimens. To the Oligocene belong the amber insects, of which 900 species are known from Baltic amber alone, and to the same epoch are ascribed the deposits of Florissant and White River in Colorado and of Green River, Wyoming. These localities—the richest in the world—have been made famous by the monumental works of Scudder. At Florissant there is an extinct lake, in the bed of nies 204" from volcanic sand and ash, the re- a mains of insects are found in aston- “LZ ishing profusion. For Miocene for Ss ot which TE Euro ean spe- Pale@oblattina douvillei, natural Ds; For) P P size.—After BRONGNIART. which, entombed in shales derived cies are known, the CEningen beds of Bavaria are celebrated as having furnished 844 species, des- cribed by the illustrious Heer. Pleistocene species are supplied by the peats of France and Europe, the lignites of Bavaria, and the interglacial clays of Switzerland and Ontario, Canada. Silurian and Devonian.—The oldest fossil insect known consists of a single hemipterous wing, Protocimex, from the Lower Silurian of Sweden. Next in age comes a wing, Paleoblattina (Fig. 294), of doubtful position,’ from the Middle Silurian of France. Following these are six speci- mens of as many remarkable species from the Devonian shales 1There is some evidence, it should be said, that this species is not an insect. Handlirsch denies also that Protocimex is an insect. 26 386 ENTOMOLOGY of New Brunswick. The specimens, to be sure, are nothing but broken wings, yet these few fragments, interpreted by Dr. Scudder, are rich in meaning. All are neuropteroid, but they cannot be classified satisfactorily with recent forms on account Platephemera antiqua, natural size.—After ScuDDER. of being highly synthetic in structure. Thus Platephemera antiqua (Fig. 295), though essentially a May fly of gigantic proportions (spreading probably 135 mm.), has an odonate type of reticulation; while Yenoneura (Fig. 296) combines characters which are now distributed among Ephemeride, Sialide, Rhaphidiide, Coniopterygide, and other families, besides being in many respects unique. These Devonian forms Fic. 206. Xenoneura antiquorwn, five times natural size.—After SCUDDER. attained huge dimensions as compared with their recent repre- sentatives; Gerephemera, for example, had an estimated ex- panse of 175 millimeters. Carboniferous.—The Carboniferous age, with its luxuriant vegetation, 1s marked by the appearance of insects in great DISTRIBUTION 387 number and variety, still restricted, however, to the more generalized orders. The dominance of cockroaches in the Carboniferous is especially noteworthy, no less than 200 Palzo- zoic species being known from Eu- rope and North America. These ancient roaches (Fig. 297) differed from their modern descendants in the similarity of the two pairs of wings, which were alike in form, size, transparency and general neu- ration, with six principal nervures FIG. 297. in each wing; while in recent cock- roaches the front wings have be- come tegmina, with certain of the veins always blended together, though the hind wings have retained their primitive characteristics with a few modifications, such as the ex- pansion of the anal area. Car- boniferous cockroaches furthermore Exupirovipositors, straight, slender — (Piblattma mazona, 2 Car boniferous cockroach from and half as long again as the abdo- Iinois. Twice natural size. men—organs which do not exist in recent species. Lithomantis (Fig. 298), a remarkable form from Scotland. possessed in addition to its four large neuropteroid wings, a pair of prothoracic wing-like appendages which, provided they may be regarded as homologous with wings, represent a third pair, either atrophied or undeveloped—a condition which is never found today, unless the patagia of Lepidoptera represent wing's, which is unlikely. From the rich deposits of Commentry, Brongniart has des- eribed several forms of striking interest. Dictyoneurais a Car- boniferous genus with neuropteroid wings and an orthopteroid body, having, in common with several contemporary genera, strong isopteran affinities. Corydaloides scudderi, a phasmid, —After ScuppEer in Miall and Denny. 388 ENTOMOLOGY has an alar expanse of twenty-eight inches. The Carbonife- rous prototypes of our Odonata were gigantic beside their modern descendants, one of them (A/eganeura) having a spread of over two feet; they were more generalized in structure than recent Odonata, presenting a much simpler type of neuration and less differentiation of the segments of the thorax. The Carboniferous precursors of our May flies attained a high Fic. 208. Lithomantis carbonarius, showing prothoracic appendages. Two thirds natural size.— After Woopwarp. development in number and variety; in fact, the Ephemeride, like the Blattidze, achieved their maximum development ages ago, when they attained an importance strongly contrasting with their present meager representation. The Permian has supplied a remarkable genus Eugereon (Fig. 299) with hemipterous mouth parts associated with fili- form antenne and orthopteroid wings. The earliest unques- tionable traces of insects with an indirect metamorphosis are found in the Permian of Bohemia, in the shape of caddis worm cases. Triassic.—Triassic cockroaches present interesting stages in the evolution of their family. Through these Mesozoic DISTRIBUTION 389 species, the continuity between Palzeozoic and recent cock- roaches is clearly established—which can be said of no other insects; and in fact of no other animals, the only comparable cases being those of the horse and the molluscan genus Planor- bis. In the Triassic period occur the first fossils that can be Fic. 299 % \ f ; I 1 g err Mion fz 7, oe ES F AGE oa2 Fed Eugereon béckingi. Three quarters natural size.—After DoHRN. referred indisputably to Coleoptera and Hymenoptera, the lat- ter order being represented first, as it happens, by some of its most specialized members, namely ants. Jurassic.—At length, in the Jurassic, all the large orders except Lepidoptera occur; Diptera appear for the first time, and Odonata are represented by many well-preserved speci- mens, while the Liassic Coleoptera studied by Heer number over one hundred species. The Cretaceous has yielded but few insects, as might be expected. Tertiary.—In the rich Tertiary deposits all orders of insects occur. Baltic amber has yielded Collembola, some remarkable Psocidze, many Diptera, and ants in abundance. Of 844 spe- 390 ENTOMOLOGY cies taken from the noted Miocene beds of Ceningen, nearly one half were Coleoptera, followed by neuropteroid forms (seventeen per cent.) and Hymenoptera (fourteen per cent.) ; ants were twice as numerous in species as they are at present in Europe. Almost half the known species of fossil insects have been described from the Miocene of Europe. To the Miocene belongs the indusial limestone of Auvergne, France, where extensive beds—in some places two or three meters deep—consist for the most part of the calcified larval cases of caddis flies. At Florissant, as contrasted with C*ningen by Scudder, Hymenoptera constitute 40 per cent. of the specimens, owing chiefly to the predominance of ants; Diptera follow with 30 per cent. and then Coleoptera with 13 per cent. Modern fam- ilies are represented in great profusion. ‘The material from Florissant and neighboring localities includes a Lepisma, fit- teen species of Psocidze, over thirty species of Aphididze, and over one hundred species of Elateridze, while the Rhynchoph- ora number 193 species as against 150. species from the Tertiary of Europe. Tuipu- lide are abundant and ex- quisitely preserved, while Bibionidz, as compared with their present numbers, are FIG. 300. vy surprisingly. common. Nu- merous masses of eggs oc- cur, undoubtedly sialid and closely like those of Cory- dalis. Sialid characters, in- Prodryas persephone, a fossil buttery Geed, appear imp the maii=s Genres Natural size.— After fossils known, and are strongly manifest through- out the fossil series, though among recent insects Sialidz oc- cupy only a subordinate place. Strange to say, few aquatic insects have been found in this ancient lake basin. Fossil butterflies are among the greatest rarities, only sev- DISTRIBUTION 391 enteen being known; yet Florissant has contributed eight of these, a few of which are marvelously well preserved (Fig. 300), as appears from Scudder’s figures. Two of the Floris- sant specimens belong to Libytheinz, a group now scantily represented, though widely distributed over the earth. The group is structurally an archaic one, and its recent members (forming only one eight-hundredth of the described species of butterflies) are doubtless relicts. Taken as a whole, the insect facies of Tertiary times was apparently much the same as at present. The Florissant fauna and flora indicate, however, a former climate in Colorado as warm as the present climate of Georgia. Quaternary.—The interglacial clays of Toronto, Ontario, have yielded fragments of the skeletons of beetles to the extent of several hundred specimens, about one third of which (chiefly elytra) were sufficiently complete or characteristic to be identified by Dr. Scudder, who has found in all 76 species of beetles, representing 8 families, chiefly Carabide and Staphylinidz. All these interglacial beetles are referable to recent genera, but none of them to recent species, though the differences between the interglacial species and their recent allies are very slight. As a whole, these species “indicate ‘a climate closely resembling that of Ontario to-day, or perhaps a slightly colder one. . . . One cannot fail, also, to notice that a large number of the allies of the interglacial forms are re- corded from the Pacific coast.”’ (Scudder.)' The writer, who has studied these specimens, has been impressed most by their likeness to modern species. It is indeed remarkable that so little specific differentiation has occurred in these beetles since the interglacial epoch—certainly ten thousand and _ possibly two or three hundred thousand years ago. General Conclusions.— Unfortunately, the earliest fossils with which we are acquainted shed much less light upon the subject of insect phylogeny than one might expect. The few Devonian forms, though synthetic indeed as compared with their modern allies, are at the same time highly organized, or 392 ENTOMOLOGY far from primitive, and their ancestors have been obliterated. The general plan of wing structure, as Scudder finds, has remained unaltered from the earliest times, though the De- vonian specimens exhibit many peculiarities of venation, in which respect some of them are more specialized than their nearest living allies, while none of them have much special relation to Carboniferous forms. Carboniferous insects are more nearly related to recent forms than are the Devonian species, but present a number of significant generalized features. Generally speaking, the tho- racic segments were similar and unconsolidated, and the two pairs of diaphanous wings were alike in every respect—in groups that have since developed tegmina and dissimilar tho- racic segments. The Carboniferous precursors of our cock- roaches, phasmids and May flies have been mentioned. Pale- ozoic insects are grouped by Scudder into a single order, Palzeodictyoptera, on account of their synthetic organization, though other authors have tried to distribute them among the modern orders. This disagreement will continue until, with increasing knowledge, our classification becomes less arbitrary and more natural. Mesozoic insects are interesting chiefly as evolutionary links, notably so in the case of cockroaches—the only insects whose ancestry is continuously traceable. In this era the large fam- ilies became differentiated out. Most of the Tertiary species are referable to recent genera, peculiar families being highly exceptional, while all the Quater- nary species belong to recent genera. Hemiptera appear in the Silurian; Neuroptera (in the old sense) in the Devonian; Thysanura and Orthoptera, Carbonif- erous ; Coleoptera and Hymenoptera, Triassic; Diptera, Juras- sic; and Lepidoptera not until the Tertiary. Cie ke XC ETD INSECTS IN RELATION TO MAN A great many insects, eminently successful from their own standpoint, so to speak, nevertheless interfere seriously with the interests of man. On the other hand, many insects are directly or indirectly so useful to man that their services form no small compensation for the damage done by other species. Injurious Insects.—Insects destroy cultivated plants, infest domestic animals, injure food, manufactured articles, etc., and molest or harm man himself. The cultivation of a plant in great quantity offers an un- usual opportunity for the increase of its insect inhabitants. The number of species affecting one kind of plant—to say nothing of the number of individuals—is often great. Thus about 200 species attack Indian corn, 50 of them doing notable injury; 200 affect clover, directly or indirectly; and 400 the apple; while the oaks harbor probably 1,000 species. The average annual loss through the cotton worm, 1860 to 1874, was $15,000,000, according to Packard; the loss from the Rocky Mountain locust, in 1874, in lowa, Missouri, Kan- sas and Nebraska, $40,000,000 (Thomas) ; and the total loss from this pest, 1874 to 1877, $200,000,000. The loss through the chinch bug, in 1864, was $73,000,000 in Illinois alone, as estimated by Riley. The ravages of the Hessian fly, fluted scale, San José scale, gypsy moth and cotton boll weevil need only be mentioned. At times, an insect has been the source of a national calam- ity, as was the case for forty years in France, when Phylloxera threatened to exterminate the vine. In Africa the migratory locust is an unmitigated evil. Probably at least ten per cent. of every crop is lost through the attacks of insects, though the loss is often so constant as 393 304 ENTOMOLOGY to escape observation. Regarded as a direct tax of ten cents upon the dollar, however, this loss becomes impressive. Web- ster says: “It costs the American farmer more to feed his insect foes than it does to educate his children.” The average annual damage done by insects to crops in the United States was conservatively estimated by Walsh and Riley to be $300,- 000,000—or about $50 for each farm. ‘“‘ A recent estimate by experts put the yearly loss from forest insect depredations at not less than $100,000,000.. The common schools of the coun- try cost in 1902 the sum of $235,000,000, and all higher insti- tutions of learning cost less than $50,000,000, making the total cost of education in the United States considerably less than the farmers lost from insect ravages. Thus it would be within the statistical truth to make a still more startling statement than Webster’s, and say, that it costs American farmers more to feed their insect foes than it does to maintain the whole system of education for everybody’s children. “ Furthermore, the yearly losses from insect ravages aggre- gate nearly twice as much as it costs to maintain our army and navy; more than twice the loss by fire; twice the capital in- vested in manufacturing agricultural implements; and nearly three times the estimated value of the products of all the fruit orchards, vineyards, and small fruit farms in the country.” (Slingerland. ) Though most of the parasites of domestic animals are merely annoyances, some inflict serious or even fatal injury, as has been said. The gad flies persecute horses and cattle; the maggots of a bot fly grow in the frontal sinuses of sheep, causing vertigo and often death; another bot fly develops in the stomach of the horse, enfeebling the animal. ‘The worst of the bot flies, however, is Hypoderma lineata, the ox-warble, which not only impairs the beef but damages the hide by its perforations; the loss from this insect for one period of six months (Chicago, 1889) was conservatively estimated as $3,336,565, of which $667,513 represented the injury to hides. All sorts of food stuffs are attacked by insects, particularly i rr air err INSECTS IN RELATION TO MAN 395 cereals; clothing, especially of wool, fur or feathers; also fur- niture and hundreds of other useful articles. As carriers of disease germs, insects are of vital importance to man, as we have shown. Beneficial Insects.—The vast benefits derived from insects are too often overlooked, for the reason that they are often so unobvious as compared with the injuries done by other spe- cies. Insects are useful as checks upon noxious insects and plants, as pollenizers of flowers, as scavengers, as sources of human clothing, food, etc., and as food for birds and fishes. Almost every insect is subject to the attacks of other insects, predaceous or parasitic—to say nothing of its many other enemies—and but for this a single species of insect might soon overrun the earth. There are only too many illustrations of the tremendous spread of an insect in the absence of its accus- tomed natural enemies. One of these examples is that of the gypsy moth, artificially introduced into Massachusetts from Europe; another is the fluted scale, transported from Australia to California. Some conception of the vast restricting influ- ence of one species upon another may be gained from the fact that the fluted scale has practically been exterminated in Cali- fornia as the result of the importation from Australia of one of its natural enemies, a lady-bird beetle known as Novis car- dinalis. The plant lice, though of unparalleled fecundity, are ordinarily held in check by a host of enemies, as was described. An astonishingly large number of parasites may develop in the body of a single individual; thus over 3,000 specimens of a hymenopterous parasite (Copidosoma truncatcllum) were reared by Giard from a single Plusia caterpillar. Parasites themselves are frequently parasitized, this phe- nomenon of hyperparasitism being of considerable economic importance. A beneficial primary parasite may be overpow- ered by a secondary parasite, evidently to the indirect disad- vantage of man, while the influence of a tertiary parasite would be beneficial again. Now parasites of the third order occur and probably of the fourth order, as appears from Howard’s 396 ENTOMOLOGY studies, which we have already summarized. Moreover, para- sites of all degrees are attacked by predaceous insects, birds, bacteria, fungi, ete. The control of one insect by another becomes, then, a subject of extreme intricacy. Insects render an important, though commonly unnoticed, service to man in checking the growth of weeds. Indeed, in- sects exercise a vast influence upon vegetation in general. A conspicuous alteration in the vegetation has followed the inva- sions of the Rocky Mountain locust, as Riley has said; many plants before unnoticed have grown in profusion and many common kinds have attained an unusual luxuriance. As agents in the cross pollination of flowers, insects are eminently important. Darwin and his followers have proved beyond question that as a rule cross pollination is indispensable to the continued vitality of flowering plants; that repeated close pollination impairs their vigor to the point of extermina- tion. Without the visits of bees and other insects our fruit trees would yield little or nothing, and the fruit grower owes these helpers a debt which is too often overlooked. As scavengers, insects are of inestimable benefit, consuming as they do in incalculable quantity all kinds of dead and decay- ing animal and vegetable matter. This function of insects is most noticeable in the tropics, where the ants, in particular, eradicate tons of decomposing matter that man lazily neglects. The usefulness of the silkworms and the honey bee need only be mentioned, and after these, the cochineal insect and the lac insects. The ‘‘ Spanish fly ’’—a meloid beetle—s still used medicinally, and in China medicinal properties are ascribed to many different insects. As human food, insects are of con- siderable importance among semi-civilized races; the migra- tory locust is eaten in great quantities in Africa, and termites in Africa and Australia, the latter insects being said to have a delicious flavor; in Mexico the eggs and adults of an aquatic hemipteron, Coriva, are highly relished by the natives. As food for fishes, game birds, song birds and poultry, insects are of vast importance, it is needless to say. INSECTS IN RELATION TO MAN 397. Introduction and Spread of Injurious Insects.— Many of our worst insect pests were brought accidentally from Europe, notably the Hessian fly, wheat midge, codling moth (prob- ably), gypsy moth, cabbage butterfly, cabbage aphis, clover leaf beetle, clover root borer, asparagus beetle, imported cur- rant worm and many cutworms; though few American species have obtained a foothold in Europe, one of the few being the dreaded Phylloxera, which appeared in France in 1863. The gypsy moth, liberated in Massachusetts in 1868, cost the state over one million dollars in appropriations (1&90- 1899) and is not yet under control. The San José scale, a native of North China according to Marlatt, was introduced into the San José valley, California, about 1870, probably upon the flowering Chinese peach, became seriously destructive there in 1873, was carried across the continent to New Jersey in 1886 or 1887 on plum stock, and thence distributed directly to several other states, upon nursery stock. At present the San José scale is a permanent menace to horticulture throughout the United States and is being checked or subdued only by the vigorous and continuous work of official entomologists, acting under special legislation. This pernicious insect occurs also in Japan, Hawaii, Australia and Chile, in these places probably as a recent introduction. The Mexican cotton boll weevil (Anthonomus grandis) crossed the Rio Grande river and appeared in Brownsville, Texas, about 1892, since when it has spread over eastern Texas and even into western Louisiana. Advancing as it does at the rate of fifty miles a year, the insect would require but fif- teen or eighteen years to cover the entire cotton belt. The beetle hibernates and lays its eggs in the cotton bolls; these are injured both by the larva feeding within and by the beetles, whose feeding-punctures destroy the bolls and cause them to drop. If unchecked, this pest would destroy fully one half the cotton crop, entailing an annual loss of $250,000,000. As it is, the universal adoption of the cultural methods recommended by the Bureau of Entomology promises to reduce the damage to a point at which cotton can still be grown at a fair profit. 398 ENTOMOLOGY An insect often passes readily from a wild plant to a nearly related cultivated species. Thus the Colorado potato beetle passed from the wild species Solanum rostratum to the intro- duced species, Solanum tuberosum, the potato. Many of our fruit tree insects feed upon wild, as well as cultivated, species of Rosaceze ; the peach borer, a native of this country, probably fed originally upon wild plum or wild cherry. Many of the common scarabeeid larvee known as “ white grubs ” are native to prairie sod, and attack the roots of various cultivated grasses, ‘ including corn, and those of strawberry, potato and other plants. The chinch bug fed originally upon native grasses, but is equally at home on cultivated species, particularly millet, Hungarian grass, rice, wheat, barley, rye and corn. In fact, the worst corn insects, such as the chinch bug, wire worms, white grubs and cutworms, are species derived from wild erasses. Even in the absence of cultivated plants their insect pests continue to sustain themselves upon wild plants, as a rule; the larva of the codling moth is very common in wild apples and wild haws. The Economic Entomologist.—To mitigate the tremen- dous damage done by insects, the individual cultivator is almost helpless without expert advice, and the immense agricultural interests of this country have necessitated the development of the economic entomologist, the value of whose services is uni- versally appreciated by the intelligent. Nearly every State now has one or more economic entomolo- gists, responsible to the State or else to a State Experiment Station, while the general Government attends to general ento- mological needs in the most comprehensive and thorough manner. “Tt is the special object of the economic entomologist,” says Dr. Forbes, “to investigate the conditions under which these enormous losses of the food and labor of the country oecur, and to determine, first, whether any of them are in any degree preventable; second, if so, how they are to be prevented INSECTS IN RELATION TO MAN 399 with the least possible cost of labor and money; and, third, to estimate as exactly as possible the expenses of such prevention, or to furnish the data for such an estimate, in order that each may determine for himself what is for his interest in every case arising. “The subject matter of this science is not insects alone, nor plants alone, nor farming alone. One may be a most excellent entomologist or botanist, or he may have the whole theory and practice of agriculture at his tongue’s end, and at his fingers’ ends as well, and yet be without knowledge or resources when brought face to face with a new practical problem in economic entomology. The subject is essentially that of the relations of these things to each other; of insect to plant and of plant to insect, and of both these to the purposes and operations of the farm, and it involves some knowledge of all of them. “As far as the entomological part of the subject is con- cerned, the chief requisites are a familiar acquaintance with the common injurious insects, and especially a thorough knowledge of their life histories, together with a practical familiarity with methods of entomological study and research. The life histories of insects lie at the foundation of the whole subject of economic entomology; and constitute, in fact, the principal part of the science; for until these are clearly and completely made out for any given injurious species, we can- not possibly tell when, where or how to strike it at its weakest point. “ But besides this, we must also know the conditions favor- able and unfavorable to it; the enemies which prey upon it, whether bird or insect or plant parasite; the diseases to which it is subject, and the effects of the various changes of weather and season. We should make, in fact, a thorough study of it in relation to the whole system of things by which it is affected. Without this we shall often be exposed to needless alarm and expense, perhaps, in fighting by artificial remedies, an insect already in process of rapid extinction by natural causes ; perhaps giving up in despair just at the time when the 400 ENTOMOLOGY natural checks upon its career are about to lend their powerful aid to its suppression. We may even, for lack of this knowl- edge, destroy our best friends under the supposition that they are the authors of the mischief which they are really exerting themselves to prevent. In addition to this knowledge of the relations of our farm pests to what we may call the natural conditions of their life, we must know how our own artificial farming operations affect them, which of our methods of cul- ture stimulate their increase, and which, if any, may help to keep it down. And we must also learn where strictly artifi- cial measures can be used to advantage to destroy them. “For the life histories of insects, close, accurate and con- tinuous observation is of course necessary; and each species studied must be followed not only through its periods of de- structive abundance, when it attracts general attention, but through its times of scarcity as well, and season after season, and year after year. “The observations thus made must of course be collected, collated and most cautiously generalized, with constant refer- ence to the conditions under which they were made. No part of the work requires more care than this. “This work becomes still more difficult and intricate when we pass from the simple life histories of insects to a study of the natural checks upon their increase. Here hundreds and even thousands of dissections of insectivorous birds and pre- daceous insects are necessary, and a careful microscopic study of their food, followed by summaries and tables of the prin- cipal results, a tedious and laborious undertaking, a specialty in itself, requiring its special methods and its special knowl- edge of the structures of insects and plants, since these must be recognized in fragments, while the ordinary student sees them only entire. “Tf we would understand the relations of season and weather to the abundance of injurious insects, we are led up to the science of meteorology; and if we undertake to master the obscure subject of their diseases, especially those of epi- INSECTS IN RELATION TO MAN 40I demic or contagious character, we shall find use for the highest skill of the microscopist, and the best instruments of micro- scopic research. “All these investigations are preliminary to the practical part of our subject. What shall the farmer do to protect his crops? To answer this question, besides the studies just men- tioned, much careful experiment is necessary. All practical methods of fighting the injurious insects must be tried—first on a small scale, and under conditions which the experimenter can control completely, and then on the larger scale of actual practice; and these experiments must be repeated under vary- ing circumstances, until we are sure that all chances of mistake or of accidental coincidence are removed. The whole subject of artificial remedies for insect depredations, whether topical applications or special modes of culture, must be gone over critically in this way. So many of the so-called experiments upon which current statements relating to the value of reme- dies and preventives are based, have been made by persons unused to investigation, ignorant of the habits and the trans- formations of the insects treated, without skill or training in the estimation of evidence, and failing to understand the i1m- portance of verification, that the whole subject is honeycombed with blunders. Popular remedies for insect injuries have, in fact, scarcely more value, as a rule, than popular remedies for disease. “Observation, record, generalization, experiment, verifica- tion—these are the processes necessary for the mastery of this subject, and they are the principal and ordinary processes of all scientific research.”’ The official economic entomologist uses every means to reach the public for whose benefit he works. Bulletins, circu- lars and reports, embodying most serviceable information, are distributed freely where they will do the most good, and timely advice is disseminated through newspapers and agricultural journals. An immense amount of correspondence is carried on with individual seekers for help, and personal influence is 27 402 ENTOMOLOGY exerted in visits to infested localities and by addresses before agricultural meetings. Special emergencies often tax every resource of the official entomologist, especially if he is ham- pered by inadequate legislative provision for his work. Too often the public, disregarding the prophetic voice of the expert, refuses to “ close the door until the horse is stolen.” Aside from these emergencies, such as outbreaks of the Rocky Mountain locust, chinch bug, Hessian fly, San José scale and others, the State or Experiment Station entomologist has his hands full in any State of agricultural importance; in fact, can scarcely discharge his duties properly without the aid of a corps of competent assistants. This chapter would be incomplete without some mention of the progress of economic entomology in this country, especially since America is pre-eminently the home of the science. The history of the science is largely the history of the State and Government entomologists, for the following account of whose work we are indebted chiefly to the writings of Dr. Howard, to which the reader is referred for additional details as well as for a comprehensive review of the status of economic ento- mology in foreign countries. Massachusetts.—Dr. Thaddeus W. Harris, though preceded as a writer upon economic entomology by William D. Peck, was our pioneer official entomologist—official simply in the sense that his classic volume was prepared and published at the expense of the state of Massachusetts, first (1841) as a “Report” and later as a “ Treatise.” The splendid) filma edition (1862), entitled “A Treatise on Some of the Insects Injurious to Vegetation,’ is still “the vade mecum of the working entomologist who resides in the northeastern section of the country.” Dr. Alpheus S. Packard gave the state three short but use- ful reports from 1871 to 1873. As entomologist to the Hatch Experiment Station of the Massachusetts Agricultural College, Prof. Charles H. Fernald has issued important bulletins upon injurious insects, and has INSECTS IN RELATION TO MAN 403 published in collaboration with Edward H. Forbush a notable volume upon the gypsy moth. For the suppression of this pest, which threatened to exterminate vegetation over one hun- dred square miles, the state of Massachusetts made annual appropriations amounting in all to more than one million dol- lars, and the operations, carried on by a committee of the State Board of Agriculture, rank among the most extensive of their kind. New York.—Dr. Asa Fitch, appointed in 1854 by the New York State Agricultural Society, under the authorization of the legislature, was the first entomologist to be officially com- missioned by any state. His fourteen reports (1855 to 1872) embody the results of a large amount of painstaking investi- gation. In 1881, Dr. James A. Lintner became state entomologist of New York. Highly competent for his chosen work, Lint- ner made every effort to further the cause of economic ento- mology, and his thirteen reports, accurate, thorough and ex- tremely serviceable, rank among the best. Lintner has had a most able successor in Dr. E. P. Felt, who is continuing the work with exceptional vigor and the most careful regard for the entomological welfare of the state. Felt has published at this writing eighteen bulletins (including seven annual reports), besides important papers on forest and shade tree insects, and has directed the preparation by Need- ham and his associates of three notable volumes on aquatic insects. The Cornell University Agricultural Experiment Station, established in 1879, has issued many valuable publications upon injurious insects, written by the master-hand of Pro- fessor Comstock or else under his influence. The studies of Comstock and Slingerland are always made in the most con- scientious spirit and their bulletins—original, thorough and practical—are models of what such works should be. Illinois.—Mr. Benjamin D. Walsh, engaged in 1867 by the Illinois State Horticultural Society, published in 1868, as act- 404 ENTOMOLOGY ing state entomologist, a report in the interests of horticulture —an accurate, sagacious and altogether excellent piece of ori- ginal work. Like many other economic entomologists he was a prolific writer for the agricultural press and his contribu- tions, numbering about four hundred, were in the highest degree scientific and practical. Walsh was succeeded by Dr. William LeBaron, who pub- lished (1871 to 1874) four able reports of great practical value. In the words of Dr. Howard, “ He records in his first report the first successful experiment in the transportation of parasites of an injurious species from one locality to another, and in his second report recommended the use of Paris green against the canker worm on apple trees, the legitimate outcome from which has been the extensive use of the same substance against the codling moth, which may safely be called one of the great discoveries in economic entomology of late years.” Following LeBaron as state entomologist, Rev. Cyrus Thomas and his assistants, G. H. French and D. W. Coquillett, produced a creditable series of six reports (1875 to 1880) as part of a projected manual of the economic entomology of Tlinois. Since 1882, Prof. Stephen A. Forbes has fulfilled the duties ‘of state entomologist in the most efficient manner. Thor- oughly scientific, with a broad view and a clear insight into the agricultural needs of the state, his authoritative and schol- arly works upon economic entomology rank with those of the highest value. Of the twelve reports issued thus far by Dr. Forbes, those dealing with the chinch bug, San José scale, corn insects and sugar beet insects are especially noteworthy. Missouri.—Appointed in 1868, Prof. Charles V. Riley pub- lished (1869 to 1877) nine reports as state entomologist. To quote Dr. Howard, ‘‘ They are monuments to the state of Mis- souri, and more especially to the man who wrote them. They are original, practical and scientific. . . . They may be said to have formed the basis for the new economic entomology of the world.” Riley’s subsequent work will presently be spoken of. INSECTS IN RELATION TO MAN 405 State Experiment Stations.—The organization of State Agricultural Experiment Stations in 1888, under the Hatch Act, gave economic entomology an additional impetus. At present, all the states and territories, except Indian Territory, have an experiment station, and in a few instances two or even three; while there are stations in Alaska, Hawaii and Porto Rico. These stations, often in connection with state agricul- tural colleges, maintain altogether over forty men who con- cern themselves more or less with entomology, and have issued a great number of bulletins upon injurious insects. These publications are extremely valuable as a means of disseminat- ing entomological information, and not a few of them are based upon the investigations of their authors. Especially noteworthy as regards originality, volume and general useful- ness are the publications of Slingerland in New York, Smith in New Jersey, Webster in Ohio (formerly), Hopkins in West Virginia, Gillette and Osborn in Iowa and Gillette in Colorado. The reports that Lugger issued in Minnesota, though compiled for the most part, contain much serviceable information, pre- sented in a popularly attractive manner. While these workers have been conspicuously active in the publication of their investigations, there are many other sta- tion entomologists who devote themselves altogether to the practical application of entomological knowledge, and whose work in this respect is highly important, even though its influ- ence does not extend beyond the limits of the state. The U.S. Entomological Commission.—This commission founded under a special Act of Congress in 1877 to investigate the Rocky Mountain locust, consisted of Dr. C. V. Riley, Dr. A. S. Packard and Rev. Cyrus Thomas, remained in existence until 1881, and published five reports and seven bulletins, all of lasting value. ‘The first two reports form a most elaborate monograph of the Rocky Mountain locust; the third report includes important work upon the army worm and the canker worm; the fourth, written by Riley, is an admirable volume on the cotton worm and boll worm; and the fifth, by Packard, is a useful treatise on forest and shade tree insects. 406 ENTOMOLOGY The U. S. Department of Agriculture.—The first ento- mological expert appointed under the general government was Townend Glover, in 1854. He issued a large number of reports (1863-1877), which “are storehouses of interesting and important facts which are too little used by the working entomologists of to-day,’ as Howard says. Glover prepared, moreover, a most elaborate series of illustrations of North American insects, at an enormous expense of labor, out of all proportion, however, to the practical value of his undertaking. Glover was succeeded in 1878 by Riley, whose achievements have aroused international admiration. He resigned ina year, after writing a report, and was succeeded by Prof. Comstock, who held office for two years, during which he wrote two important volumes (published respectively in 1880 and 1881) dealing especially with cotton, orange and scale insects. His work on scale insects laid the foundation for all our subsequent investigation of the subject. Riley, assuming the office of government entomologist, pub- lished up to 1894, ‘‘ 12 annual reports, 31 bulletins, 2 special reports, 6 volumes of the periodical bulletin Insect Life, and a large number of circulars of information.” During his vigorous and enterprising administration economic entomology took an immense step in advance. The life histories of injuri- ous insects were studied with extreme care and many valuable improvements in insecticides and insecticide machinery were made. One of the notable successes of Dr. Riley and his co- workers, which has attracted an exceptional amount of public attention, was the practical extermination of the fluted scale (Icerya purchasi), which threatened to put an end to the cul- tivation of citrus trees in California. This disaster was averted by the importation from Australia, in 1888, of a native enemy of the scale, namely, the lady-bird beetle Novius (Vedalia) cardinalis, which, in less than eighteen months after its introduction into California, subjugated the noxious scale insect. The United States has since sent Novius to South Africa, Egypt and Portugal with similar beneficial results. a INSECTS IN RELATION TO MAN AO7 Based upon the foundation laid by Riley, the work of the Division (now the Bureau) of Entomology has steadily pro- gressed, under the leadership of Dr. Leland O. Howard. With a comprehensive and firm grasp of his subject, alert to discover and develop new possibilities, energetic and resourceful in management, Dr. Howard has brought the government work in applied entomology to its present position of commanding importance. Admirably organized, the Bureau now maintains a corps of about fifty experts, and the total output of the Divi- sion and the Bureau now amounts to nearly one hundred bul- letins and more than half as many circulars. The Department of Agriculture has recently succeeded in starting a new and important industry in California—the cul- ture of the Smyrna fig. The superior flavor of this variety is due to the presence of ripe seeds, or, in other words, to fertilization, and for this it 1s necessary for pollen of the wild fig, or “caprifig,’ to be transferred to the flowers of the Smyrna fig. Normally this pollination, or “ caprification,” is dependent upon the services of a minute chalcid, Blastoph- aga grossorum, which develops in the gall-like flowers of the caprifig. The female insect, which in this exceptional in- stance is winged while the male is not, emerges from the gall covered with pollen, enters the young flowers of the Smyrna fig to oviposit, and incidentally pollenizes them. After many discouraging attempts, Blastophaga, imported from Algeria, has now been established in California, and the new industry 1s developing rapidly. Canada.—The development of economic entomology in Canada has been due largely to the efforts of Dr. James Fletcher, of the Dominion Experimental Farms, Ottawa, whose annual reports and other writings indicate ability of an exceptional order. His work has been furthered in every way by the “eminent director of the experimental farms system, Dr. William Saunders, himself a pioneer in economic ento- mology in Canada and the author of one of the most valuable treatises upon the subject that has ever been published in America.” 408 ENTOMOLOGY Outside of this, the work in Canada centers around the Entomological Society of Ontario, whose excellent publica- tions, sustained by the government, are of great scientific and educational importance. In addition to its annual reports, this society issues the Canadian Entomologist, one of the leading serials of its kind, edited by its founder, the Rev. ©. Ji 3: Bethune, whose devoted services are appreciated by every entomologist. The Association of Official Economic Entomologists.— Organized in 1889 by a few energetic workers, this association has had a rapid and healthy growth and now numbers among its members all the leading economic entomologists of America and a large number of foreign workers. The annual meetings of the association impart a vigorous stimulus to the individual worker and tend to promote a well-balanced development of the science of economic entomology. Conclusion.—While working for the material welfare of the agriculturist, the economic entomologist discovers phe- nomena which are of the highest value to the purely scientific mind. Indeed it is remarkable to notice the extent to which the professedly practical entomologist is animated—not to say dominated—hby the same spirit which has led many of the most profound thinkers that the world has ever produced to devote their lives to the study of life itself. BIE RATURE The literature on entomological subjects now numbers scarcely less than 100,000 titles. The works listed below have been selected chiefly on account of their general usefulness and accessibility. Works incidentally containing important bibliographies of their special subjects are designated each by an asterisk—*. BIBLIOGRAPHICAL WORKS Hagen, H. A. Bibliotheca Entomologica. 2 vols. Leipzig, 1862-1863. Covers the entire literature of entomology up to 1862. Engelmann, W. Bibliotheca Historico-Naturalis. 1 vol. Leipzig, 1846. Literature, 1700-1846. Carus, J. V., and Engelmann, W. Bibliotheca Zoologica. 2 vols. Leipzig, 1861. Literature, 1846-1860. Taschenberg, O. Bibliotheca Zoologica. 5 vols. Leipzig, 1887-1899. Vols. 2 and 3, entomological literature, 1861-1880. The Zoological Record. London. Annually since vol. for 1864. Catalogue of Scientific Papers, Royal Society. London. Since 1868. Zoologischer Anzeiger. Leipzig. Fortnightly since 1878. Bibliographica Zoologica, annual volumes since 1896. Concilium Bibliographicum. Zurich. Card catalogue of current zoological literature since 1896. Archiv fiir Naturgeschichte. Berlin. Annual summaries since 1835. Journal of the Royal Microscopical Society. London. Summaries of the most important works, beginning 1878. Zoologischer Jahresbericht. - Leipzig. Yearly summaries of literature since 1879. Zoologisches Centralblatt. Leipzig. Reviews of more important litera- ture since 1895. Psyche. Cambridge, Mass. Records of recent American literature. Also earlier records, beginning 1874. Entomological News. Philadelphia, 1890 to date. Records of current lit- erature up to 1903. Bibliography of the more important contributions to American Economic Entomology. 8 parts. Pts. 1-5 by S. Henshaw; pts. 6-8 by N. Banks. 1318 pp. Washington, 1889-10905. Catalogue of Scientific Serials, 1633-1876. S. H. Scudder. Cambridge, Mass. Harvard University, 1879. A Catalogue of Scientific and Technical Periodicals, 1665-1895. H. C. Bolton. Washington, Smithsonian Institution, 1897. 409 410 ENTOMOLOGY A List of Works on North American Entomology. N. Banks. Bull. U. S. Dept. Agric., Div. Ent., no. 24 (n. s.), 95 pp. Washington, Igoo. GENERAL ENTOMOLOGY Kirby, W., and Spence, W. 1822-26. An Introduction to Entomology. 4 vols. 36-+ 2413 pp., 30 pls. London. Burmeister, H. 1832-55. Handbuch der Entomologie. 2 vols. 28+ 1746 pp., 16 taf. Trans. of Band 1: 1836. W. E. Shuckard. A Man- ual of Entomology. 12+ 654 pp., 32 pls. London. Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects. 2 vols. 23-+ 620 pp., 133 figs. London. Graber, V. 1877-79. Die Insekten. 2 vols. 8+ 1008 pp., 404 figs. Munchen. Miall, L. C., and Denny, A. 1886. The Structure and Life-History of the Cockroach. 6+ 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson. Comstock, J. H. 1888. An Introduction to Entomology. 4-+ 234 pp., 201 figs. Ithaca, N. Y. Kolbe, H. J. 1889-93. Einftthrung in die Kenntnis der Insekten. 12+ 709 pp., 324 figs. Berlin. F. Diimmler.* Packard, A. S. 1889. Guide to the Study of Insects. Ed. 9. 12+ 715 pp., 668 figs., 15 pls. New York. Henry Holt & Co. Hyatt, A., and Arms, J. M. 1890. Insecta. 23+ 300 pp., 13 pls., 223 figs. Boston. D. C. Heath & Co.* Kirby, W. F. 1892. Elementary Text-Book of Entomology. Ed. 2. 8+ 281 pp., 87 pls. London. Swan Sonnenschein & Co. Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7+ 701 pp., 797 figs., 6 pls. Ithaca, N. Y. Comstock Pub. Co. Sharp, D. 1895, 1901. Insects. Cambr. Nat. Hist., vols. 5, 6. 12+ 1130 pp., 618 figs. London and New York. Macmillan & Co.* Comstock, J. H. 1897, 1901. Insect Life. 6-+ 349 pp., 18 pls., 206 figs. New York. D. Appleton & Co. Packard, A. S. 1898. A Text-Book of Entomology. 17+ 729 pp., 654 figs. New York and London. The Macmillan Co.* Carpenter, G. H. 1899. Insects; their Structure and Life. 11+ 404 pp., 184 figs. London. J. M. Dent & Co.* Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16+ 367 pp., 273 figs. New York. Henry Holt & Co.* Howard, L. O. 1901. The Insect Book. 27+ 429 pp., 48 pls., 264 figs. New York. Doubleday, Page & Co. Hunter, S. J. 1902. Elementary Studies in Insect Life. 18+ 344 pp., 234 figs. Topeka. Crane & Co. Henneguy, L. F. 1904. Les Insectes. Morphologie, Reproduction, Em- bryogénie. 18+ 804 pp., 622 figs., 4 pls. Paris. Masson et Cie.* Kellogg V. L. 1905. American Insects. 7+ 674 pp., 13 pls., 812 figs. New York. Henry Holt & Co. LITERATURE AII PHYLOGENY AND CLASSIBICATION Kirby, W., and Spence, W. 1822-26. An Introduction to Entomology. 4 vols. 36+ 2413 pp., 30 pls. London. Burmeister, H. 1832. Handbuch der Entomologie. 2 vols. 28-+ 1746 pp., 16 taf. Berlin. Translation of Band 1: 1836. W. E. Shuck- ard. A Manual of Entomology. 12-+654 pp., 32 pls. London. Contains useful synopses of the older systems of classification. Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects. 2 vols. 23+ 620 pp., 133 figs. London. Miller, F. 1864. Fir Darwin. Leipzig. Trans.: 1869. W. S. Dallas. Facts and Figures in aid of Darwin. London. Brauer, F. 1869. Betrachtungen uber die Verwandlung der Insekten im Sinne der Descendenz-Theorie. Varh. zool.-bot. Gesell. Wien, bd. 19, pp. 299-318; bd. 28 (1878), 1870, pp. 151-166. Lubbock, J. 1873. On the Origin of Insects. Journ. Linn. Soc. Zool. vol. II, pp. 422-425. Packard, A. S. 1873. Our Common Insects. 225 pp., 268 figs. Boston. Estes & Lauriat. Lubbock, J. 1874. On the Origin and Metamorphoses of Insects. 16+ 108 pp., 63 figs., 6 pls. London. Macmillan & Co.* Mayer, P. 1876. Ueber Ontogenie und Phylogenie der Insekten. Jenais. Zeits. Naturw., bd. 10, pp. 125-221, taf. 6-6c. Wood-Mason, J. 1879. Morphological Notes bearing on the Origin of Insects. Trans. Ent. Soc. London, pp. 145-167, figs. I-9. Haase, E.. 1881. Beitrag zur Phylogenie und Ontogenie der Chilopoden. Zeits. Ent. Breslau, bd. 8, heft 2, pp. 93-115. Lankester, E. R. 1881. Limulus an Arachnid. Quart. Journ. Micr. Sce., vol. 21 (n. s.), pp. 504-548, 609-649, pls. 28, 20, figs. I-20. Packard, A. S. 1881. Scolopendrella and its Position in Nature. Amer. Nat., vol. 15, pp. 698-704, fig. I. Kingsley, J. S. 1883. Is the Group Arthropoda a valid one? Amer. Nat., vol. 17, pp. 1034-1037. Packard, A. S. 1883. The Systematic Position of the Orthoptera in rela- tion to Other Orders of Insects. Third Rept. U. S. Ent. Comm., pp. 286-304. Brauer, F. 1885. Systematisch-zoologische Studien. Sitzb. Akad. Wiss. Wien, bd. 91, pp. 237-413.* Grassi, B. 1885. I progenitori degli Insetti e dei Miriapodi—Morfologia delle Scolopendrelle. Atti. Accad. Torino, t. 21, pp. 48-50. Haase, E. 1886. Die Vorfahren der Insecten. Sitzb. Abh. Isis Dresden, pp. 85-01. Claus, C. 1887. On the Relations of the Groups of Arthropoda. Ann. Mas. Nat. Hist., ser. 5, vol. 19; p. 306. Kingsley, J. S. 1888. The Classification of the Myriapoda. Amer. Nat., vol. 22, pp. 1118-1121. AI2 ENTOMOLOGY Haase, E. 1889. Die Abdominalanhange der Insekten mit Berticksichti- gung der Myriopoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. Tis US. Fernald, H. T. 1890. The Relationships of Arthropods. Studies Biol. Lab. Johns Hopk. Univ., vol. 4, pp. 431-513, pls. 48-50. Hyatt, A.. and Arms, J. M. 1890. Insecta. 23-+ 300 pp., 13 pls., 223 figs. Boston. D. C. Heath & Co.* Cholodkowsky, N. 1892. On the Morphology and Phylogeny of Insects. Ann. Mag. Nat. Hist., ser. 6, vol. 10, pp. 429-451. Grobben, C. 1893. A Contribution to the Knowledge of the Genealogy and Classification of the Crustacea. Ann. Mag. Nat. Hist., ser. 6, vol. II, pp. 440-473. Trans. from Sitzb. Akad. Wiss. Wien, math.-nat. Cl., bd. tor, heft 2, pp. 237-274, taf. 1. Hansen, H. J. 1893. A Contribution to the Morphology of the Limbs and Mouth-parts of Crustaceans and Insects. Ann. Mag. Nat. Hist., ser. 6, vol. 12, pp. 417-434. Trans. from Zool. Anz., jhg. 16, pp. 193-198, 201-212. Pocock, R. I. 1893. On some Points in the Morphology of the Arachnida (s. s.) with Notes on the Classification of the Group. Ann. Mag. Nat. Hist., ser. 6, vol. 11, pp. 1-10, pls. I, 2. Pocock, R. I. 1893. On the Classification of the Tracheate Arthropoda. Zool. Anz., jhg. 16, pp. 271-275. Bernard, H. M. 1894. The Systematic Position of the Trilobites. Quart. Journ. Geol. Soc. London, vol. 50, pp. 411-434, figs. I-17. Kingsley, J. S. 1894. The Classification of the Arthropoda. Amer. Nat., vol. 28, pp. 118-135, 220-235.* Kenyon, F. C. 1895. The Morphology and Classification of the Pauro- poda, with Notes on the Morphology of the Diplopoda. Tufts Coll. Studies, no. 4, pp. 77-146, pls. I-3. Schmidt, P. 1895. Beitrage zur Kenntnis der niederen Myriapoden. Zeits. wiss. Zool., bd. 50, pp. 436-510, taf. 26, 27. Wagner, J. 1895. Contributions to the Phylogeny of the Arachnida. Ann. Mag. Nat. Hist., ser. 6, vol. 15, pp. 285-315. Trans. from Jenais. Zeits. Naturw., bd. 29, pp. 123-156. Miall, L. C. 1895. The Transformations of Insects. Nature, vol. 53, pp- 152-158. Sedgwick, A. 1895. Peripatus. Camb. Nat. Hist., vol. 5, pp. 1-26, figs. I-14. Sinclair, F. G. 1895. Myriapoda. Camb. Nat. Hist., vol. 5, pp. 27-80, figs. 15-46. Sharp, D. 1895, 1901. Insects. Camb. Nat. Hist., vols. 5, 6. 12-+ 1130 pp., 618 figs. London and New York. Macmillan & Co.* Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7-1+.701 pp., 797 figs., 6 pls. Ithaca, N. Y. Comstock Pub. Co. Heymons, R. 1896. Zur Morphologie der Abdominalanhange bei den Insecten. Morph. Jahrb., bd. 24, pp. 178-204, 1 taf. LITERATURE 413 Heymons, R. 1897. Mittheilungen iiber die Segmentierung und den Korperbau der Myriopoden. Sitzb. Akad. Wiss., Berlin, bd. 40, Pp. 915-023, 2 figs. Hansen, H. J., and Sérensen, W. 1897. The Order Palpigradi Thor. and its Relationship to the Arachnida. Ent. Tidsk., arg. 18, pp. 223- 240, pl. 4. Hutton, F. W., and others. 1897. Are the Arthropoda a Natural Group? Nat. Sc., vol. 10, pp. 97-117. Lankester, E. R. 1897. Are the Arthropoda a Natural Group? Nat. Sc., vol. Io, pp. 264-268. Packard, A. S. 1898. A Text-Book of Entomology. 17+ 729 pp., 654 figs. New York and London. The Macmillan Co.* Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16+ 367 pp., 273 figs. New York. Henry Holt & Co.* Von Zittel, K. A. 1900, 1902. Text-Book of Paleontology. 2 vols. Trans. C. R. Eastman. London and New York. Macmillan & Co.* Folsom, J. W. 1900. The Development of the Mouth Parts of Anurida maritima Guér. Bull. Mus. Comp. Zool., vol. 36, pp. 87-157, pls. 1-8.* Hansen, H. J. 1902. On the Genera and Species of the Order Pauropoda. Vidensk. Medd. Naturh. Foren. Kjobenhavn (1901), pp. 323-424, pls. 1-6. Carpenter, G. H. 1903. On the Relationships between the Classes of the Arthropoda. Proc. R. Irish Acad., vol. 24, pp. 320-360, pl. 6.* Enderlein, G. 1903. Ueber die Morphologie, Gruppierung und systemat- ische Stellung der Corrodentien. Zool. Anz., bd. 26, pp. 423- 437, 4 figs. Hansen, H. J. 1903. The Genera and Species of the Order Symphyla. Quart. Journ. Micr. Sc., vol. 47, pp. 1-101, pls. 1-7. Packard, A. S. 1903. Hints on the Classification of the Arthropoda; the Group, a Polyphyletic One. Proc. Amer. Phil. Soc., vol. 42, pp. 142-161. Lankester, E. R. 1904. The Structure and Classification of the Arthro- poda. Quart. Journ. Micr. Sc., vol. 47 (n. s.), pp. 523-582, pl. 42. (From Encyc. Britt., ed. Io.) Carpenter, G. H. 1905. Notes on the Segmentation and Phylogeny of the Arthropoda, with an Account of the Maxille in Polyxenus lag- urus. Quart. Journ. Micr. Sc., vol. 49, pt. 3, pp. 469-4901, pl. 28.* GENERAL ANATOMY De Réaumur, R. A. F. 1734-42. Mémoires pour servir a l’histoire des insectes. 7 vols. Paris. Lyonet, P. 1762. Traité anatomique de la Chenille, qui ronge le Bois de Saule. Ed. 2. 22-++ 616 pp., 18 pls. La Haye. Straus-Diirckheim, H. 1828. Considérations générales sur l’anatomie comparée des animaux articulés, etc. 19-+ 434 pp., 10 pls. Paris. 414 ENTOMOLOGY Newport, G. 1839. Insecta. Todd’s Cyclopedia Anat. Phys., vol. 2, pp. 853-094, figs. 3290-430. Leydig, F. 1851. Anatomisches und Histologisches tiber die Larve von Corethra plumicornis. Zeits. wiss. Zool., bd. 3, pp. 435-451, taf. 16, figs. I-4. Leydig, F. 1855. Zum feineren Bau der Arthropoden. Miiller’s Archiv Anat. Phys., pp. 376-480, taf. 3. Leydig, F. 1857. Lehrbuch der Histologie des Menschen und der Thiere. 12+ 551 pp., figs. Frankfurt. Leydig, F. 1859. Zur Anatomie der Insecten. Muiller’s Archiv Anat. Phys., pp. 33-89, 149-183, taf. 3. Leydig, F. 1864. Vom Bau des tierischen Korpers. Tiibingen. Huxley, T. H. 1877. A Manual of the Anatomy of Invertebrated Ani- mals. London. J. and A. Churchill. 1878. New York. OD. Appleton & Co. Packard, A. S., and Minot, C. S. 1878. Anatomy and Embryology [of the locust]. First Rept. U. S. Ent. Comm., pp. 257-270, figs. 12-18. Washington. Lubbock, J. 1879. On the Anatomy of Ants. Trans. Linn. Soc. Zool., ser. 2, vol. 2, pp. 141-154, pls. Riley, C. V., Packard, A. S., and Thomas C. 1880, 1883. Second and Third Repts. U. S. Ent. Comm. Washington. Minot, C. S. 1880. Histology of the Locust (Caloptenus) and the Cricket (Anabrus). Second Rept. U. S. Ent. Comm., pp. 183-222, pls. 2-8. Washington. Brooks, W. K. 1882. Handbook e Invertebrate Zoology, pp. Fee figs. 129-141. Boston. S. E. Cassino. Viallanes, H. 1882. Recherches sur l’histologie des insectes. Ann. Sc. nat. Zool., sér. 6, t. 14, pp. 1-348, pls. 1-18. Leydig, F. 1883. Untersuchungen zur Anatomie und Histologie der Thiere. 174 pp., 8 taf. Bonn. Miall, L. C., and Denny, A. 1886. The Structure and Life-history of the Cockroach. 6-+ 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson. Schaeffer, C. 1889. Beitrage zur Histologie der Insekten. Zool. Jahrb., Morph. Abth., bd. 3, pp. 611-652, taf. 29, 30. Lowne, B. T. 1890-92. The Anatomy, Physiology, Morphology and De- velopment of the Blow-fly (Calliphora erythrocephala). A Study in the Comparative Anatomy and Morphology of Insects. 8+ 779. DP. LOS Less eet plse london: Lang, A. 1891. Text-Book of Comparative Anatomy. Trans. by H. M. and M. Bernard. Pt. 1, pp. 438-508, figs. 301-356. London and New York. Macmillan & Co.* Comstock, J. H., and Kellogg, V. L. 1899. The Elements of Insect Anat- omy. Rev. ed. 134 pp., 11 figs. Ithaca, N. Y. Comstock Pub- lishing Co. LITERATURE 415 HEAD AND APPENDAGES Schaum, H. 1863. Uber die Zusammensetzung des Kopfes und die Zahl der Abdominalsegmente bei den Insekten. Archiv Naturg., jhg. 29, bd. I, pp. 247-260. Basch, S. 1865. Skelett und Muskeln des Kopfes von Termes. Zeits. wiss. Zool., bd. 15, pp. 55-75, I taf. Breitenbach, W. 1877. Vorlatifige Mitteilung uber einige neue Unter- suchungen an Schmetterlingsrtisseln. Archiv mikr. Anat., bd. 14, pp. 308-317, 1 taf. Breitenbach, W. 1878. Untersuchungen an Schmetterlingsriisseln. Ar- chiv mikr. Anat., bd. 15; pp. 8-20, 1 taf. Breitenbach, W. 1879. Ueber Schmetterlingsrtissel. Ent. Nachr., jhe. 5, PP. 237-243. Burgess, E. 1880. Contributions to the Anatomy of the Milk-weed But- terfly (Danais archippus Fabr.). Anniv. Mem. Bost. Soc. Nat. Hist., 16 pp., 2 pls. Meinert, F. 1880. Sur la conformation de la téte et sur l’interprétation des organes buccaux chez les Insectes, ainsi que sur la systéma- tique de cet ordre. Ent. Tidsk., arg. I, pp. 147-150. Dimmock, G. 1881. The Anatomy of the Mouth Parts and of the Suck- ing Apparatus of some Diptera. 50 pp., 4 pls. Boston. A. Williams & Co.* Geise, O. 1883. Die Mundtheile der Rhynchoten. Archiv Naturg., jhg. 49, bd. I, pp. 315-373, taf. Io. Kraepelin, K. 1883. Zur Anatomie und Physiologie des Rtissels von Musca. Zeits. wiss. Zool., bd. 39, pp. 683-719, taf. 4o, 41. _ Briant, T. J. 1884. On the Anatomy and Functions of the Tongue of the Honey Bee (worker). Journ. Linn. Soc. Zool., vol. 17, pp. 408- 417, pls. 18, Io. Wedde, H. 1885. Beitrage zur Kenntniss des Rhynchotenrtissels. Ar- Chivas Natures, yng si. bd. 1, pp, 113=142, tak 6) 7: Walter, A. 1885. Beitrage zur Morphologie der Schmetterlinge. Jenais. Zeits. Naturw., bd. 18, pp. 751-807, taf. 23, 24. Walter, A. 1885. Zur Morphologie der Schmetterlingsmundtheile. Jenais. Zeits. Naturw., bd. 10, pp. 19-27. Breithaupt, P. F. 1886. Ueber die Anatomie und die Functionen der Bienenzunge. Archiv Naturg., jhg. 52, bd. 1, pp. 47-112, taf. 4, 5.* Blanc, L. 1891. La téte du Bombyx mori a l'état larvaire, anatomie et physiologie. Trav. Lab. Etud. Soie, 1889-1890, 180 pp., 95 figs. Lyon. Smith, J. B. 1892. The Mouth Parts of Copris carolina; with Notes on the Homologies of the Mandibles. Trans. Amer. Ent. Soc., vol. 19, pp. 83-87, pls. 2, 3. Hansen, H. J. 1893. A Contribution to the Morphology of the Limbs and Mouth Parts of Crustaceans and Insects. Ann. Mag. Nat. Hist., ser. 6, vol. 12, pp. 417-434. Trans. from Zool. Anz., jhg. 16, pp. 193-198, 201-212. 416 ENTOMOLOGY Kellogg, V. L. 1895. The Mouth Parts of the Lepidoptera. Amer. Nat., vol. 29, pp. 546-556, pl. 25, figs. I, 2. Smith, J. B. 1896. An Essay on the Development of the Mouth Parts of certain Insects. Trans. Amer. Phil. Soc., vol. 19 (n. s.), pp. 175-108, pls. 1-3. Folsom, J. W. 1899. The Anatomy and Physiology of the Mouth Parts of the Collembolan, Orchesella cincta L. Bull. Mus. Comp. Zool., vol. 35, pp. 7-39, pls. 1-4.* Janet, C. 1899. Essai sur la constitution morphologique de la téte de Vinsecte. 74 pp., 7 pls. Paris. G. Carré et C. Naud. Kellogg, V. L. 1899. The Mouth Parts of the Nematocerous Diptera. Psyche, vol. 8, pp. 303-306, 327-330, 346-348, 355-359, 363-365, figs. I-II. Folsom, J. W. 1900. The Development of the Mouth Parts of Anurida maritima Guér. Bull. Mus. Comp. Zool., vol. 36, pp. 87-157, pls. 1-8.* Comstock, J. H., and Kochi, C. 1902. The Skeleton of the Head of In- sects. Amer. Nat., vol. 36, pp. 13-45, figs. I1-29.* Kellogg, V. L. 1902. The Development and Homologies of the Mouth Parts of Insects. Amer. Nat., vol. 36, pp. 683-706, figs. 1-26. Meek, W. J. 1903. On the Mouth Parts of the Hemiptera. Kansas Univ. Sc. Bull., vol. 2 (12), pp. 257-277, pls. 7—-11.* Holmgren, N. 1904. Zur Morphologie des Insektenkopfes. Zeits. wiss. Tolle; ial 740, {Os ABO, eh, 27, ASG Kulagin, N. 1905. Der Kopfbau bei Culex und Anopheles. Zeits. wiss. Zool., bd. 83, pp. 285-335, taf. 12-14.* THORAX AND APPENDAGES; LOCOMOTION Audouin, J. V. 1824. Recherches anatomiques sur le thorax des animaux articulés et celui des insectes hexapodes en particulier. Ann. Sc. nat. Zool, t. I. pp. 97-135, 416-432, figs. MacLeay, W. S. 1830. Explanation of the comparative anatomy of the thorax in winged insects, with a review of the present state of the nomenclature of its parts. Zool. Journ., vol. 5, pp. 145-170, 2 pls. Langer, K. 1860. Ueber den Gelenkbau bei den Arthrozoen. Vierter Beitrag zur vergleichenden Anatomie und Mechanik der Gelenke. Denks. Akad. Wiss. Wien., Phys. Cl., bd. 18, pp. 99-140, 3 taf. West, T. 1861. The Foot of the Fly; its Structure and Action; eluci- dated by comparison with the feet of other Insects, ete. Trans. Linn. Soc. Zool., vol. 23, pp. 393-421, pls. 41-43. Plateau, F. 1871. Qu’est-ce que l’aile d’un Insecte? Stett. ent. Zeit., % jhg. 32, pp. 33-42, pl. 1. Plateau, F. 1872. Recherches expérimentales sur la position du centre de gravité chez les insectes. Archiv. Sc. phys. nat. Genéve, nouv. Det t 43h DP: 5-37 LITERATURE 417 Pettigrew, J. B. 1874. Animal Locomotion. 13 -+ 264 pp., 130 figs. New York. D. Appleton & Co. Marey, E. J. 1874, 1879. Animal Mechanism. 16-+ 283 pp., 117 figs. New York. D. Appleton & Co. Hammond, A. 1881. On the Thorax of the Blow-fly (Musca vomitoria). Journ. Linn. Soc. Zool., vol. 15, pp. 9-31, pls. I, 2. Von Lendenfeld, R. 1881. Der Flug der Libellen. Ein Beitrag zur Anat- omie und Physiologie der Flugorgane der Insecten. Sitzb. Akad. Wiss. Wien., bd. 83, pp. 289-376, taf. 1-7. Brauer, F. 1882. Ueber das Segment médiaire Latreille’s. Sitzb. Akad. Wiss. Wien, bd. 85, pp. 218-244, taf. 1-3. Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine. Archiv Naturg., jhg. 50, bd. 1, pp. 146-193, taf. II-13. Dewitz, H. 1884. Ueber die Fortbewegung der Thiere an senkrechten glatten Flachen vermittelst eines Sekretes. Pfltiger’s Archiv ges. Phys., bd. 33, pp. 440-481, taf. 7-9. Graber, V. 1884. Ueber die Mechanik des Insektenk6rpers. I. Mechanik der Beine. Biol. Centralbl., bd. 4, pp. 560-570. Amans, P. 1885. Comparaisons des organes du vol dans la série animale. Ann. Sc. nat. Zool., sér. 6, t. 19, pp. 1-222, pls. 1-8. Redtenbacher, J. 1886. Vergleichende Studien tiber das Fligelgeader der Insecten. Ann. naturh. Hofm. Wien, bd. I, pp. 153-232, taf. 9-20. Amans, P. C. 1888. Comparaisons des organes de la locomotion aqua- tique. Ann. Sc. nat. Zool., sér. 7, t. 6, pp. 1-164, pls. 1-6. Carlet, G. 1888. Sur le mode de locomotion des chenilles. Compt. rend. Acad. Sc., t. 107, pp. 131-134. Ockler, A. 1890. Das Krallenglied am Insektenfuss. Archiv Naturg., jhg. 56, bd. 1, pp. 221-262, taf. 12, 13. : Demoor, J. 1891. Recherches sur la marche des Insectes et des Arach- nides. Archiv. Biol., t. 10, pp. 567-608, pls. 18-20. Hoffbauer, C. 1892. Beitrage zur Kenntnis der Insektenfltigel. Zeits. wiss. Zool., bd. 54, pp. 579-630, taf. 26, 27, 3 figs.* Spuler, A. 1892. Zur Phylogenie und Ontogenie des Fltigelgedader der Schmetterlinge. Zeits. wiss. Zool., bd. 53, pp. 597-046, taf. 25, 26. Comstock, J. H. 1893. Evolution and Taxonomy. Wilder Quarter- Century Book, pp. 37-114, pls. 1-3. Ithaca, N. Y. Kellogg, V. L. 1895. The Affinities of the Lepidopterous Wing. Amer. Nat., vol. 29, pp. 709-717, figs. IIo. Marey, E. J. 1895. Movement. 15+ 323 pp.,.204 figs. New York. D. Appleton & Co. Comstock, J. H., and Needham, J. G. 1898-99. The Wings of Insects. Amer. Nat., vols. 32, 33, pp. 43-48, 81-80, 231-257, 335-340, 413- 424, 561-565, 760-777, 903-QII, 117-126, 573-582, 845-860, figs. I-90. Reprint, Ithaca, N. Y. Comstock Pub. Co. Walton, L. B. 1900. The Basal Segments of the Hexapod Leg. Amer. Nat., vol. 34, pp. 267-274, figs. 1-6. 418 ENTOMOLOGY Verhoeff, K. W. 1902. Beitrage zur vergleichenden Morphologie des Thorax der Insekten mit Berticksichtigung der Chilopoden. Nova Acta Leop.-Carol. Akad. Naturf., bd. 81, pp. 63-110, taf. 7-13. Voss, F. 1904-05. Uber den Thorax von Gryllus domesticus. Zeits. wiss. Zool., bd. 78, pp. 268-521, taf. 15, 16, 25 figs. ABDOMEN AND APPENDAGES Lacaze-Duthiers, H. 1849-53. Recherches sur l’armure génitale femelle des insectes. Ann. Sc. nat Zool., sér. 3, t. 12-19, pls. Several papers. Fenger, W. H. 1863. Anatomie und Physiologie des Giftapparates bei den Hymenopteren. Archiv Naturg., jhg. 29, bd. I, pp. 139-178, Tact Schaum, H. 1863. Ueber die Zusammensetzung des Kopfes und die Zahl der Abdominalsegmente bei den Insekten. Archiv Naturg., jhg. 29, bd. I, pp. 247-260. Sollmann, A. 1863. Der Bienenstachel. Zeits. wiss. Zool., bd. 13, pp. 528-540, I taf. Packard, A. S. 1866. Observations on the Development and Position of the Hymenoptera, with Notes on the Morphology of Insects. Proc. Bost. Soc. Nat. Hist., vol. 10, pp. 279-295, figs. 1-4. Goossens, T. 1868. Notes sur les pattes membraneuses des Chenilles. Ann. Soc. ent. France, sér. 4, t. 8, pp. 745-748. Packard, A. S. 1868. On the Structure of the Ovipositor and Homol- ogous Parts in the Male Insect. Proc. Bost. Soc. Nat. Hist., vol. II, pp. 393-399, figs. I-IT. Graber, V. 1870. Die Aehnlichkeit im Baue der ausseren weiblichen Geschlechtsorgane bei den Locustiden und Akridiern dargestellt auf Grund ihrer Entwicklungsgeschichte. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 61, pp. 507-616, taf. Scudder, S. H., and Burgess, E. 1870. On Asymmetry in the Appendages. of Hexapod Insects, especially as illustrated in the Lepidopterous. Genus Nisoniades. Proc. Bost. Soc. Nat. Hist., vol. 13, pp. 282- 306, I pl. Krapelin, C. 1873. Untersuchungen tiber den Bau, Mechanismus und die Entwicklungsgeschichte des Stachels der bienenartigen Thiere. Zeits. wiss. Zool., bd. 23, pp. 289-330, taf. 15, 16. Dewitz, H. 1875. Ueber Bau und Entwickelung des Stachels und der Legescheide einiger Hymenopteren und der griinen Heuschrecke. Zeits. wiss. Zool., bd. 25, pp. 174-200, taf. 12, 13. White, F. B. 1876. On the Male Genital Armature in the Rhopalocera. Trans. Linn. Soc. Zool., ser. 1, vol. 1, pp. 357-369, 3 pls. Adler, H. 1877. Lege-Apparat und Eierlegen der Gallwespen. Deuts. ent. Zeits., jhg. 21, pp. 305-332, taf. 2. Dewitz, H. 1877. Ueber Bau und Entwickelung des Stachels der Amei- sen. Zeits. wiss. Zool., bd. 28, pp. 527-556, taf. 26. LITERATURE 419 Davis, H. 1879. Notes on the Pygidia and Cerci of Insects. Journ. R. Micr. Soc., vol. 2, pp. 252-255. Kraatz, G. 1881. Ueber die Wichtigkeit der Untersuchung des mann- lichen Begattungsgliedes der Kafer fur die Systematik und Artun- terscheidung. Deuts. ent. Zeits., jhg. 25, pp. 113-126. Dewitz, H. 1882. Ueber die Fiithrung an den Korperhangen der Insecten. Berlin ent. Zeits., bd. 26, pp. 51-68, fig. Gosse, P. H. 1882. On the Clasping Organs ancillary to Generation in certain Groups of the Lepidoptera. Trans. Linn. Soc. Zool., ser. 2, vol. 2, pp. 265-345, 8 pls. Von Hagens, D. 1882. Ueber die mannlichen Genitalien der Bienen-Gat- tung Sphecodes. Deuts. ent. Zeits., jhg. 26, pp. 209-228, taf. 6, 7. Radoszkowski, 0. 1884. Révision des armures copulatrices des males du genre Bombus. Bull. Soc. Nat. Moscou, t. 49, pp. 51-02, 4 pls. Saunders, E. 1884. Further notes on the terminal segments of Aculeate Hymenoptera. Trans. Ent. Soc. London, pp. 251-267. Haase, E. 1885. Ueber sexuelle Charactere bei Schmetterlingen. Zeits. Ent. Breslau, n. f., bd. 9, pp. 15-19; bd. 10, pp. 36-44. Radoszkowski, 0. 1885. Révision des armures copulatrices des males de la famille des Mutillide. Hore Soc. Ent. Ross., t. 19, pp. 3-49, 9 pls. Von Ihering, H. 1886. Der Stachel der Meliponen. Ent. Nachr., jhg. 12, pp. 177-188, taf. 8. Goossens, T. 1887. Les pattes des Chenilles. Ann. Soc. ent. France, sér. 6, t. 7, pp. 385-404, pl. 7. Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. Morph. Jahrb., bd. 13, pp. 586-615, taf. 25, 26. Haase, E. 1889. Ueber Abdominalanhange bei Hexapoden. Sitzb. Gesell. naturf. Freunde, pp. 19-20. Haase, E. 1889. Die Abdominalanhange der Insekten mit Berticksichti- gung der Myriopoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. 14, I5. Radoszkowski, 0. 1889. Révision des armures copulatrices des males de la tribu des Chrysides. Hore Soc. Ent. Ross., t. 23, pp. 3-40, pls. 1-6. Beyer, 0. W. 1890. Der Giftapparat von Formica rufa, ein reduziertes Organ. Jenais. Zeits. Naturw., bd. 25, pp. 26-112, taf. 3, 4. Carlet, G. 1890. Mémoire sur le venin et l’aiguillon de l’abeille. Ann. Semncie4ooleasct: 7.6 On Ppl I—l7apl: TL: Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of Lepidopterous larve. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pls. 1, 2. Sharp, D. 1890. On the structure of the terminal segment in some male Hemiptera. Trans. Ent. Soc. London, pp. 399-427, pls. 12-14. Wheeler, W. M. 1890. On the Appendages of the first abdominal Seg- ment of embryo Insects. Trans. Wis. Acad. Sc., vol. 8, pp. 87- 140, pls. 1-3.* 420 ENTOMOLOGY Escherich, K. 1892. Die biologische Bedeutung der Genitalanhange der Insekten. Verh. zool.-bot. Ges. Wien, bd. 42, pp. 225-240, taf. 4. Graber, V. 1892. Ueber die morphologische Bedeutung der Abdominalan- hange der Insekten-Embryonen. Morph. Jahrb., bd. 17, pp. 467- 482. Escherich, K. 1894. Anatomische Studien tiber das mannliche Genital- system der Coleopteren. Zeits. wiss. Zool., bd. 57, pp. 620-641, taf. 26, 3 figs. ; Janet, C. 1894. Sur la Morphologie du squelette des segments post- thoraciques chez les Myrmicides. Note 5. Mém. Soc. acad. Oise, t. I5, pp. 591-611, figs. I-5. Pérez, J. 1894. De l’organe copulateur male des Hyménoptéres et de sa valeur taxonomique. Ann. Soc. ent. France, t. 63, pp. 74-S1, figs. 1-8. Verhoeff, C. 1894. Vergleichende Untersuchungen tiber die Abdominal- segmente der weiblichen Hemiptera-Heteroptera und Homoptera. Verh. nat. Ver. Bonn, jhg. 50, pp. 307-374. Heymons, R. 1895. Die Seginentirung des Insectenkorpers. Anh. Abh. Preuss. Akad. Wiss. Berlin, 39 pp., I taf. Heymons, R. 1895. Die Embryonalentwickelung von Dermapteren und Orthopteren unter besonderer Beriicksichtigung der Keimblatter- bildung. - 136 pp:, 12 taf, 33 figs. Jiena. Peytoureau, S. A. 1895. Contribution a l’étude de la morphologie de Yarmure génitale des Insectes. 248 pp., 22 pls., 43 figs. Paris. Verhoeff, S. 1895. Beitrage zur vergleichenden Morphologie des Abdo- mens der Coccinelliden, etc. Archiv Naturg., jhg. 61, bd. 1, pp. TCO Laie —o: Verhoeff, C. 1895. Vergleichend-morphologische Untersuchungen tiber das Abdomen der Endomychiden, Erotyliden und Languriiden (im alten Sinne) und tiber die Muskulatur des Copulationsap- parates von Triplex. Archiv Naturg., jhg. 61, bd. I, pp. 213-287, aliiy A, 11gy ; Verhoeff, C. 1895. Cerci und Styli der Tracheaten. Ent. Nachr., jhg. 21, pp. 166-168. Heymons, R. 1896. Grundztige der Entwickelung und des K6rperbaues von Odonaten und Ephemeriden. Anh. Abh. Akad. Wiss. Berlin, 66 pp., 2 taf. Heymons, R. 1896. Zur Morphologie des Abdominalanhange bei den Insekten. Morph. Jahrb., bd. 24, pp. 178-204, taf. I. Verhoeff, C. 1896. Zur Morphologie der Segmentanhange bei Insecten und Myriopoden. Zool. Anz., bd. 19, pp. 378-383, 385-388. Goddard, M. F. 1897. On the Second Abdominal Segment in a few Libel- lulide. Proc. Amer. Phil. Soc., vol. 35, pp. 205-212, 2 pls. Janet, C. 1897. Limites morphologiques des anneaux post-céphaliques et Musculature des anneaux post-thoraciques chez la Myrmica rubra. Note 16. 35 pp., 10 figs. Lille. Verhoeff, C. 1897. Bemerkungen tiber abdominale Korperanhange bei Insecten und Myriopoden. Zool. Anz., bd. 20, pp. 293-300. LITERATURE A2ZI Janet, C. 1898. Aiguillon de la Myrmica rubra. Appareil de fermeture de la glande a venin. Note 18. 27 pp., 3 pls. Paris. Zander, E. 1903. Beitrage zur Morphologie der mannlichen Geschlechts- anhange der Lepidopteren. Zeits. wiss. Zool., bd. 74, pp. 557- 615, taf. 20, figs. I-15.* INTEGUMENT Dufour, L. 1824-26. Recherches anatomiques sur les Carabiques et sur plusieurs autres Coléoptéres. Ann. Sc. nat. Zool., t. 2-8, pls. Several papers. Karsten, H. 1848. MHarnorgane des Brachinus complanatus. Miiller’s Archiv Anat. Phys., pp. 367-374, fig. Leydig, F. 1855. Zum feineren Bau der Arthropoden. Miuiller’s Archiv Anat. Phys., pp. 376-480, taf. 3. Semper, C. 1857. Beobachtungen tiber die Bildung der Flugel, Schuppen und Haare bei den Lepidopteren. Zeits. wiss. Zool., bd. 8, pp. 326-330, taf. 15. Sirodot, S. 1858. Recherches sur les sécrétions chez les Insectes. Ann. Sc. nat. Zool., sér. 4, t. 10, pp. 141-189, 251-334, 12 pls. Claus, C. 1861. Ueber die Seitendriisen der Larve von Chrysomela populi. Zeits. wiss. Zool., bd. 11, pp. 309-314, taf. 25. Landois, H. 1864. Beobachtungen itber das Blut der Insecten. Zeits. wiss. Zool., bd. 14, pp. 55-70, taf. 7-0. Landois, H. 1871. Beitrage zur Entwicklungsgeschichte der Schmetter- lingsflugel in der Raupe und Puppe. Zeits. wiss. Zool., bd. 21, PP. 305-316, taf. 23. Candéze, E. 1874. Les moyens d’attaque et de défense chez les Insectes. Bull. Acad. roy. Belgique, sér. 2, t. 38, pp. 787-816. Chun, C. 1876. Ueber den Bau, die Entwickelung und physiologische ‘ Bedeutung der Rektaldriisen bei den Insekten. Abh. Senckenb. naturf. Gesell., bd. 10, pp. 27-55, 4 taf. Separate, 1875, 31 pp., 4 taf. Frankfurt a. M. Miller, F. 1877. Ueber Haarpinsel, Filzflecke und ahnliche Gebilde auf den Flugeln mannlicher Schmetterlinge. Jenais Zeits. Naturw., bd. II, pp. 99-114. Scudder, S. H. 1877. Antigeny or Sexual Dimorphism in Butterflies. Proc. Amer. Acad. Arts Sc., vol. 12, pp. 150-158. Edwards, W. H. 1878. On the Larve of Lyc. pseudargiolus and atten- dant Ants. Can. Ent., vol. 10, pp. 131-136, fig. 8. Forel, A. 1878. Der Giftapparat und die Analdriisen der Ameisen. Zeits. wiss. Zool., bd. 30, supp., pp. 28-68, taf. 3, 4. Miller, F. 1878. Die Duftschuppen der Schmetterlinge. Ent. Nachr., jhg. 4, pp. 29-32. Saunders, E. 1878. Remarks on the Hairs of some of our British Hy- menoptera. Trans. Ent. Soc. London, pp. 169-172, pl. 6. 422 ENTOMOLOGY Schneider, R. 1878. Die Schuppen aus den verschiedenen Fltgel- und _ Korperteilen der Lepidopteren. Zeits. gesammt. Naturw., bd. 51, pp. 1-59. Weismann, A. 1878. Ueber Duftschuppen. Zool. Anz., jhg. 1, pp. 98, 99. Goossens, T. 1881. Des chenilles urticantes, etc. Ann. Soc. ent. France. t. I, pp. 231-236. Scudder, S. H. 1881. Butterflies; Their Structure, Changes and Life- Histories, with Special Reference to American Forms. 9 - 322 pp., 201 figs. New York. Henry Holt. & Co. Dimmock, G. 1882. On some Glands which open externally on Insects. Psyche, vol. 3, pp. 387—401.* Klemensiewicz, S. 1882. Zur naheren Kenntniss der Hautdriisen bei den Raupen und bei Malachius. Verh. zool.-bot. Gesell. Wien, bd. 32, Pp. 459-474, 2 taf. Dimmock, G. 1883. The Scales of Coleoptera. Psyche, vol. 4, pp. I-11, 23-27, 43-47, 63-71, figs. I-II. Osten-Sacken, C. R. 1884. An Essay on Comparative Chetotaxy, or the Arrangement of characteristic Bristles of Diptera. Trans. Ent. Soc. London, pp. 497-517. Simmermacher, G. 1884. Untersuchungen uber Haftapparate an Tarsal- gliedern von Insekten. Zeits. wiss. Zool., bd. 40, pp. 481-556, taf. 25-27, 2 figs. Dahl, F. 1885. Die Fussdrtisen der Insekten. Archiv mikr. Anat., bd. AI, DN; AAO AG, Wahi, 1D, Wh Witlaczil, E. 1885. Die Anatomie der Psylliden. Zeits. wiss. Zool., bd. 2, pp. 569-638, taf. 20-22. Goossens, T. 1886. Des chenilles vésicantes. Ann. Soc. ent. France, sér. 6, t. 6, pp. 461—-464.* Minot, C. S. 1886. Zur Kenntniss der Insektenhaut. Archiv mikr. Anat., bd. 28, pp. 37-48, taf. 7. Schaffer, C. 1889. Beitrage zur Histologie der Insekten. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 611-652, taf. 20, 30. Fernald, H. T. 1890. Rectal Glands in Coleoptera. Amer. Nat., vol. 24, PP LOO TO plss Anes: Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of lepidopterous larve. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pls. 1, 2. Borgert, H. 1891. Die Hautdrtisen der Tracheaten. 81 pp., taf. Jena. Thomas, M. B. 1893. The Androconia of Lepidoptera. Amer. Nat., vol. 27, pp. 1018-1021, pls. 22, 23. Cuénot, L. 1894. Le rejet de sang comme moyen de défense chez quel- ques Coléoptéres. Compt. rend. Acad. Sc., t. 118, pp. 875-877. Kellogg, V. L. 1894. The Taxonomic Value of the Scales of the Lepidop- tera. Kansas Univ. Quart., vol. 3, pp. 45-89, pls. 9, 10, figs. I-17. Packard, A. S. 1894. A Study of the Transformations and Anatomy of Lagoa crispata, a Bombycine Moth. Proc. Amer. Phil. Soc., vol. 2, pp. 275-202, pls. 1-7. LITERATURE 423 Lutz, K. G. 1895. Das Bluten der Coccinelliden. Zool. Anz., jhg. 18, PP. 244-255, I fig. Packard, A. S. 1895-96. The Eversible Repugnatorial Scent Glands of Iiisectsee our ON) Yo Ett SOC. voll 3) pp, 110-127, pl 5; vol) 4, pp. 26-32.* Spuler, A. 1895. Beitrag zur Kenntniss des feineren Baues und der Phy- logenie der Flugelbedeckung der Schmetterlinge. Zool. Jahrb., Abth. Anat. Ont., bd. 8, pp. 520-543, taf. 36. Mayer, A. G. 1896. The Development of the Wing Scales and their Pig- ment in Butterflies and Moths. Bull. Mus. Comp. Zool., vol. 20, pp. 209-236, pls. 1-7.* Bordas, L. 1897. Description anatomique et étude histologique des glandes a venin des Insectes hyménoptéres. 53 pp., 2 pls. Paris. Cuénot, L. 1897. Sur la saignée réflexe et les moyens de défense de quelques Insectes. Arch. Zool. exp., sér. 3, t. 4, pp. 655-080, 4 figs. Hilton, W. A. 1902. The Body Sense Hairs of Lepidopterous Larve. Amer. Nat., vol. 36, pp. 561-578, figs. 1-23.* Tower, W. L. 1902. Observations on the Structure of the Exuvial Glands and the Formation of the Exuvial Fluid in Insects. Zool. Anz., bd. 25, pp. 466-472, figs. 1-8. Tower, W. L. 1903. The Development of the Colors and Color Patterns of Coleoptera, with Observations upon the Development of Color in Other Orders of Insects. Univ. Chicago, Decenn. Publ., vol. 10, 140 pp., 3 pls. Plotnikow, W. 1904. Uber die Hautung und tber einige Elemente der Haut bei den Insekten. Zeits. wiss. Zool., bd. 76, pp. 333-366, iis Diy AA, 2 intersy MUSCULAR SYSTEM Lyonet, P. 1762. Traité anatomique de la Chenille, qui ronge le Bois de Saule. Ed. 2. 22-+ 616 pp., 18 pls. La Haye. Straus-Diirckheim, H. 1828. Considérations générales sur l’anatomie comparée des animaux articulés, etc. 434 pp., Io pls. Paris. Newport, G. 1839. Insecta. Todd’s Cyclopedia Anat. Phys., vol. 2, pp. 853-094, figs. 320-439. Lubbock, J. 1859. On the Arrangement of the Cutaneous Muscles of the Larva of Pygera bucephala. Trans. Linn. Soc. Zool., vol. 22, pp. 163-191, 2 pls. Basch, S. 1865. Skelett und Muskeln des Kopfes von Termes. Zeits: wiss. Zool., bd. 15, pp. 55-75, 1 taf. Plateau, F. 1865, 1866. Sur la force musculaire des insectes. Bull. Acad. roy. Belgique, sér. 2, t. 20, pp. 732-757; t. 22, pp. 283-308. Merkel, F. 1872, 1873. Der quergestreifte Muskel. Archiv mikr. Anat., bd. 8, pp. 244-268, 2 taf.; bd. 9, pp. 293-307. Lubbock, J. 1877. On some Points in the Anatomy of Ants. Month. Micr. Journ., vol. 18, pp. 121-142, pls. 189-1092. Lubbock, J. 1879. On the Anatomy of Ants. Trans. Linn. Soc. Zool., ser. 2, vol. 2, pp. 141-154, 2 pls. 424 ENTOMOLOGY Poletajeff, N. 1879. Du développement des muscles d’ailes chez les Odo- nates. Horz Soc. Ent. Ross., t. 16, pp. 10-37, 5 pls. Von Lendenfeld, R. 1881. Der Flug der Libellen. Ein Beitrag zur Anat- omie und Physiologie der Flugorgane der Insecten. Sitzb. Akad. Wiss. Wien, bd. 83, pp. 280-376, taf. 1-7. Luks, C. 1883. Ueber die Brustmuskulatur der Insecten. Jenais. Zeits. Naturw., bd. 16, pp. 529-552, taf. 22, 23. Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine. Archiv Naturg., jhg. 50, bd. I, pp. 146-193, taf. TI-13. : Van Gehuchten, A. 1886. Etude sur la structure intime de la cellule mus- culaire striée. La Cellule, t. 2, pp. 280-453, pls. 1-6. Miall, L. C., and Denny, A. 1886. The Structure and Life-history of the Cockroach. London and Leeds.* (See pp. 71-84.) Kolliker, A. 1888. Zur Kenntnis der quergestreiften Muskelfasern. Zeits. wiss. Zool., bd. 47, pp. 689-710, taf. 44, 45. Biitschli, 0., und Schewiakoff, W. 1891. Ueber den feineren Bau der quergestreiften Muskeln von Arthropoden. Biol. Centralb., bd. DE; DD. 43-30. 128. l—/. . Rollet, A. 1891. Ueber die Streifen N (Nebenscheiben), das Sarko- plasma und Contraktion der quergestreiften Muskelfasern. Ar- chiv mikr. Anat., bd. 37, pp. 654-684, taf. 37. Janet, C. 1895. Etudes sur les Fourmis, les Guépes et les Abeilles. Note 12. Structure des Membranes articulaires des Tendons et des Muscles (Myrmica, Camponotus, Vespa, Apis). 26 pp., II figs. Limoges. Janet, C. 1895. Sur les Muscles des Fourmis, des Guépes et des Abeilles. Compt. rend. Acad. Sc., t. 121, pp. 610-613, 1 fig. NERVOUS SYSTEM Newport, G. 1832, 1834. On the Nervous System of the Sphinx Ligustri Linn., and on the changes which it undergoes during a part of the Metamorphoses of the Insect. Phil. Trans. Roy. Soc. London, vol. 122, pp. 383-308, 2 pls.* Part Il. Phil) Deans Rowe sec London, vol. 124, pp. 389-423, 5 pls. Blanchard, E. 1846. Recherches anatomiques et zoologiques sur le sys- | téme nerveux des animaux sans vertebres. Du systeme nerveux des insectes. Ann. Sc. nat. Zool., sér. 3, t. 5, pp. 273-379, 8 pls. Leydig, F. 1857. Lehrbuch der Histologie des Menschen und der Thiere. 12-+ 551 pp., figs. Frankfurt. Leydig, F. 1864. Vom Bau des Tierischen Korpers. Tubingen. Brandt, E. 1876. Recherches anatomiques et morphologiques sur le sys- téme nerveux des Insectes Hyménoptéres. Compt. rend. Acad. Sc., t. 83, pp. 613-616. Dietl, M. J. 1876. Die Organisation des Arthropodengehirns. Zeits. wiss. Zool., bd. 27, pp. 488-517, taf. 36-38. LITERATURE 425 Flégel, J. H. L. 1878. Ueber den einheitlichen Bau des Gehirns in den verschiedenen Insecten-Ordnungen. Zeits. wiss. Zool., bd. 30, Brandt, E. 1879. [Many articles on the nervous system.] Hore Soc. Ent. Ross., bd. 14-15, taf.* Newton, E. T. 1879. On the Brain of the Cockroach, Blatta orientalis. Quart. Journ. Micr. Soc., n. s., vol. 19, pp. 340-356, pls. 15, 16. Michels, H. 1880. Beschreibung des Nervensystems von Oryctes nasicor- nis im Larven-, Puppen- und Kaferzustande. Zeits. wiss. Zool., bd. 34, pp. 641-702, taf. 33-36. Packard, A. S. 1880. The Brain of the Locust. Second Rept. U. S. Ent. Comm., pp. 223-242, pls. 9-15, fig. 9. Washington.* Cattie, J. T. 1881. Beitrage zur Kenntnis der Chorda supra-spinalis der Lepidoptera und des centralen, peripherischen und sympathischen Nervensystems der Raupen. Zeits. wiss. Zool., bd. 35, pp. 304- 320, taf. 16. Koestler, M. 1883. Ueber das Eingeweidenervensystem von Periplaneta orientalis. Zeits. wiss. Zool., bd. 39, pp. 572-595, taf. 34. Viallanes, H. 1884-87. Etudes histologiques et organologiques sur les centres nerveux et les organes des sens des animaux articulés. Memur—Say Anim aSe) mats Zool, ser Oy 4 17-1os Ser Ge te) 4 22 pls. Leydig, F. 1885. Zelle und Gewebe. Neue Beitrage zur Histologie des Tierkorpers. 219 pp., 6 taf. Bonn. . Viallanes, H. 1887. Sur la morphologie comparée du cerveau des Insectes et des Crustacés. Compt. rend. Acad. Sc., t. 104, pp. 444-447. Binet, A. 1894. Contribution a l’étude du system nerveux sous-intestinal des insectes. Journ. Anat. Phys., t. 30, pp. 449-580, pls. 12-15, 23 figs. Pawlovi, M. I. 1895. On the Structure of the Blood-Vessels and Sympa- thetic Nervous System of Insects, particularly Orthoptera. Works Lab. Zool. Cab. Imp. Univ. Warsaw, pp. 96-+ 22, tab. 1-6. In Russian. Holmgren, E. 1896. Zur Kenntnis des Hauptnervensystems der Arthro- poden. Anat. Anz., bd. 12, pp. 449-457, 7 figs. Kenyon, F. C. 1896. The Brain of the Bee. Journ. Comp. Neurol., vol. 6: pp. 133-210, pls, 14—22: Kenyon, F.C. 1896. The meaning and structure of the so-called “ mush- room bodies” of the hexapod brain. Amer. Nat., vol. 30, pp. 643- 650, I fig. Kenyon, F. C. 1897. The optic lobes of the bee’s brain in the light of recent neurological methods. Amer. Nat., vol. 31, pp. 369-376, pl. 9. SENSE ORGANS; SOUNDS Miller, J. 1826. Zur vergleichenden Physiologie des Gesichtsinnes der Menschen und der Tiere. 462 pp., 8 taf. Leipzig. 426 ENTOMOLOGY Von Siebold, C. T. E. 1844. Ueber das Stimm- und Gehor-Organ der Orthopteren. Archiv Naturg. jhg. 10, pp. 52-81, fig. Gottsche, C. M. 1852. Beitrag zur Anatomie und Physiologie des Auges der Krebse und Fliegen. Miiller’s Archiv Anat. Phys., pp. 483- 492. Claparéde, E. 1859. Zur Morphologie der zusammengesetzten Augen bei den Arthropoden. Zeits. wiss. Zool., bd. 10, pp. 191-214, 3 taf. Hensen, V. 1866. Ueber das Gehororgan von Locusta. Zeits. wiss. Zool., bd. 16, pp. 190-207, I taf. Landois, H. 1868. Das Geh6rorgan des Hirschkafers. Archiy mikr. Anat., bd. 4, pp. 88-95. Schultze, M. 1868. Untersuchungen uber die zusammengesetzten Augen der Krebse und Insekten. 8+ 32 pp., 12 taf. Bonn. Scudder, S. H. 1868. The Songs of the Grasshoppers. Amer. Nat., vol. 2, pp. 113-120, 5 figs. Scudder, S. H. 1868. Notes on the Stridulation of Grasshoppers. Proc. Bost. Soc. Nat. Hist., vol. 11, pp. 306-313. Graber, V. 1872. Bemerkungen tiber die Gehor- und Stimmorgane der Heuschrecken und Cicaden. Sitzb. Akad. Wiss. Wien, math.- naturw. Cl., bd. 66, pp. 205-213, 2 figs. Paasch, A. 1873. Von den Sinnesorganen der Insekten im Allgemeinen, von Gehor- und Geruchsorganen im Besondern. Archiv Naturg., jhg. 30, bd. I, pp. 248-275. Forel, A. 1874. Les fourmis de la Suisse. Neue Denks. allg. Schweiz. Gesell. Naturw., bd. 26, 480 pp., 2 taf. Separate, 1874, 4 +457 pp., 2 taf. Geneve. Mayer, A. M. 1874. Experiments on the supposed Auditory Apparatus of the Mosquito. Amer. Nat., vol. 8, pp. 577-592, fig. 92. Ranke, J. 1875. Beitrage zu der Lehre von den Uebergangs-Sinnesor- ganen. Das Gehororgan der Acridier und das Sehorgan der Hirudineen. Zeits. wiss. Zool., bd. 25, pp. 143-164, taf. Io. Schmidt, O. 1875. Die Gehororgane der Heuschrecken. Archiv mikr. Anat., bd. 11, pp. 195-215, taf. 10-12. Graber, V. 1876. Die tympanalen Sinnesapparate der Orthopteren. Denks. Akad. Wiss. Wien, bd. 36, pp. 1-140, Io taf. Graber, V. 1876. Die abdominalen Tympanalorgane der Cicaden und Gryllodeen. Denks. Akad. Wiss. Wien, bd. 36, pp. 273-206, 2 taf. Mayer, P. 1877. Der Tonapparat der Cikaden. Zeits. wiss. Zool., bd. 28, pp. 79-92, 3 figs. Forel, A. 1878. Beitrag zur Kenntniss der Sinnesempfindungen der In- sekten. Mitth. Mtinch. ent. Vereins, jhg. 2, pp. I-21. Lowne, B. T. 1878. On the Modifications of the Simple and Compound Eyes of Insects. Phil. Trans. Roy. Soc. London, vol. 169, pp. 577-602, pls. 52-54. Graber, V. 1879. Ueber neue, otocystenartige Sinnesorgane der Insekten. Archiv mikr. Anat., bd. 16, pp. 35-37, 2 taf. LITERATURE 427 Grenacher, H. 1879. Untersuchungen tiber das Sehorgan der Arthro- poden, insbesondere der Spinnen, Insekten und Crustaceen. 8-+ 188 pp., 11 taf. Gottingen. Hauser, G. 1880. Physiologische und histiologische Untersuchungen tber das Geruchsorgan der Insekten. Zeits. wiss. Zool., bd. 34, pp. 367-403, taf. 17-109. Graber, V. 1882. Die chordotonalen Sinnesorgane und das Gehor der Insecten. Archiv mikr. Anat., bd. 20, pp. 506-640, taf. 30-35, 6 figs.; bd. 21, pp. 65-145, 4 figs.* Lubbock, J. 1882. Ants, Bees and Wasps. 19+ 448 pp., 5 pls., 31 figs. London. 1884, 1901, New York. D. Appleton & Co. Graber, V. 1883. [Fundamentalversuche tiber die Helligkeits- und Far benempfindlichkeit augenloser und geblendeter Tiere. Sitzb. Akad. Wiss. Wien, bd. 87, pp. 201-236. Carriére, J. 1884. On the Eyes of some Invertebrata. Quart. Journ. Micr. Sc., vol. 24 (n. s.), pp. 673-681, pl. 45. Graber, V. 1884. Grundlinien zur Erforschung des Helligkeits und Far- bensinnes der Tiere. 8-+ 322 pp. Prag und Leipzig. Lee, A. B. 1884. Bemerkungen tiber den feineren Bau der Chordotonal- Organe. Archiv mikr. Anat., bd. 23, pp. 133-140, taf. 7b. Lowne, B. T. 1884. On the Compound Vision and the Morphology of the Eye in Insects. Trans. Linn. Soc. Zool., vol. 2, pp. 389-420, pls. 40-43. Carriére, J. 1885. Die Sehorgane der Thiere, vergleichend anatomisch dargestellt. 6-+ 205 pp., 1 taf., 147 figs. Muinchen und Leipzig. R. Oldenbourg. Hickson, S. J. 1885. The Eye and Optic Tract of Insects. Quart. Journ. Micr. Sc., vol. 25, pp. 215-251, pls. 15-17. Plateau, F. 1885. Expériences sur le role des palpes chez les Arthro- podes maxillés. Palpes des Insectes broyeurs. Bull. Soc. zool. France, t. 10, pp. 67-90. Plateau, F. 1885-88. Recherches expérimentales sur la vision chez les Insectes. Bull. Acad. roy. Belgique, sér. 3, t. 10, 14, 15, 16. Meém. Acad. roy. Belgique, t. 43, pp. I-OI. Will, F. 1885. Das Geschmacksorgan der Insekten. Zeits. wiss. Zool., bd. 42, pp. 674-707, taf. 27. Forel, A. 1886-87. Expériences et remarques critiques sur les sensations des Insectes. Rec. zool. suisse, t. 4, pp. I-50, 145-240, pl. I. Graber, V. 1887. Neue Versuche uber die Funktion der Insektenfthler. Biol. Centralb., bd. 7, pp. 13-109. Mark, E. L. 1887. Simple Eyes in Arthropods. Bull. Mus. Comp. Zool., vol. 13, pp. 49-105, pls. I-5. Patten, W. 1887. Eyes of Molluscs and Arthropods. Journ. Morph., vol. I, pp. 67-02, pl. 3. Will, F. 1887. A. Forel. Sur les Sensations des Insectes. Ent. Nachr., jhg. 13, pp. 227-233. 428 ENTOMOLOGY Patten, W. 1887, 1888. Studies on the Eyes of Arthropods. I. Develop- ment of the Eyes of Vespa, with Observations on the Ocelli of some Insects. Journ. Morph., vol. 1, pp. 193-226, 1 pl. II. Eyes of Acilius. Journ. Morph., vol. 2, pp. 97-190, pls. 7-13. Lubbock, J. 1888, 1902. On the Leas Instincts and Intelligence of Animals, with Special Reference to Insects. 29+ 292 pp., 118 figs. New York. D. Appleton & Co. Vom Rath, O. 1888. Ueber die Hautsinnesorgane der Insekten. Zeits. wiss. Zool., bd. 46, pp. 413-454, taf. 30, 31. Ruland, F. 1888. Beitrage zur Kenntnis der antennalen Sinnesorgane der Insekten. Zeits. wiss. Zool., bd. 46, pp. 602-628, taf. 37. Lowne, B. T. 1889. On the Structure of the Retina of the Blowfly (Cal- liphora erythrocephala). Journ. Linn. Soc. Zool., vol. 20, pp. 406- AIG ple Packard, A. S. 1889. Notes on the Epipharynx, and the Epipharyngeal Organs of Taste in Mandibulate Insects. Psyche, vol. 5, pp. 193- 199, 222-228. Pankrath, O. 1890. Das Auge der Raupen und Phryganidenlarven. Zeits. wiss. Zool., bd. 49, pp. 690-708, taf. 34, 35. Stefanowska, M. 1890. La disposition histologique du pigment dans les yeux des Arthropodes sous l’influence de la lumiére directe et de lobscurité compléte. Rec. zool. suisse, t. 5, pp. 151-200, pls. 8, 9. Watase, S. 1890. On the Morphology of the Compound Eyes of Arthro- pods. Studies Biol. Lab. Johns Hopk. Univ., vol. 4, pp. 287-334, pls. 29-35. Weinland, E. 1890. Ueber die Schwinger (Halteren) der Dipteren. Zeits. wiss. Zool., bd. 51, pp. 55-166, taf. 7—11. Exner, S. 1891. Die Physiologie der fazettierten Augen von Krebsen und Insekten. 8+ 206 pp., 8 taf., 23 figs. Leipzig und Wien. Von Adelung, N. 1892. Beitrage zur Kenntnis des tibialen Gehorapparates der Locustiden. Zeits. wiss. Zool., bd. 54, pp. 316-349, taf. 14, 15. Nagel, W. 1892. Die niederen Sinne der Insekten. 68 pp., 19 figs. Tubingen. Child, C. M. 1894. Ein bisher wenig beachtetes antennales Sinnesorgan der Insekten, mit besonderer Beriicksichtigung der Culiciden und Chironomiden. Zeits. wiss. Zool., bd. 58, pp. 475-528, taf. 30, 31. Mallock, A. 1894. Insect Sight and the Defining Power of Composite Eyes. Proc. Roy. Soc. London, vol. 55, pp. 85-90, figs. 1-3. Vom Rath, 0. 1896. Zur Kenntnis der Hautsinnesorgane und des sen- siblen Nervensystems der Arthropoden. Zeits. wiss. Zool., bd. 61, PP. 499-539, taf. 23, 2 Redikorzew, W. t1goo. Untersuchungen tiber den Bau der Ocellen der Insekten. Zeits. wiss. Zool., bd. 68, pp. 581-624, taf. 39, 40, figs. I-7. Reuter, E. 1896. Ueber die Palpen der Rhopaloceren, etc. Acta Soc. Se. Fenn., t. 22, pp. 16-+- 578, 6 tab. LITERATURE 429 Hesse, R. 1901. Untersuchungen tiber die Organe der Lichtempfindung bei niederen Thieren. VII. Von den Arthropoden-Augen. Zeits. wiss. Zool., bd. 70, pp. 347-473, taf. 16-21, figs. I, 2. Schenk, 0. 1903. Die antennalen Hautsinnesorgane einiger Lepidopteren und Hymenopteren mit besonderer Berticksichtigung der sexuellen Unterschiede. Zool. Jahrb., Abth. Anat. Ont., bd. 17, pp. 573-618. fabe2ta 22) Aehes.* DIGESTIVE, SYSTEM Dufour, L. 1824-60. [Many important papers.]| Am. Sc. nat. Zool. Basch, S. 1858. Untersuchungen iiber das chylopoetische und uropoetische System der Blatta orientalis. Sitzb. Akad. Wiss. Wien, math.- naturw. Cl., bd. 33, pp. 234-260, 5 taf. Sirodot, S. 1858. Recherches sur les sécrétions chez les Insectes. Ann. Sc. nat. Zool., sér. 4, t. 10, pp. 141-189, 251-334, 12 pls. Leydig, F. 1859. Zur Anatomie der Insecten. Miuller’s Archiy Anat. Phys., pp. 33-89, 149-183, 3 taf. Fabre, J. L. 1862. Etude sur le role du tissu adipeux dans la sécrétion urinaire chez les Insectes. Ann. Sc. nat. Zool., sér. 4, t. 19, pp. 351-382. Plateau, F. 1874. Recherches sur les phénomeénes de la digestion chez les Insectes. Mém. Acad. roy. Belgique, t. 41, 124 pp., 3 pls. De Bellesme, J. 1876. Physiologie comparée. Recherches expérimentales sur la digestion des insectes et en particulier de la blatte. 7+ 96 pp., 3 pls. Paris. Helm, F. E. 1876. Ueber die Spinndrtisen der Lepidopteren. Zeits. wiss. Zool., bd. 26, pp. 434-469, taf. 27, 28. Plateau, F. 1877. Note additionelle au Mémoire sur les phénoménes de la digestion chez les Insectes. Bull. Acad. roy. Belgique, sér. 2, t. 44, Pp. 710-733. Wilde, K. F. 1877. Untersuchungen ttber den Kaumagen der Orthop- teren. Archiv Naturg., jhg. 43, bd. 1, pp. 135-172, 3 taf. De Bellesme, J. 1878. Travaux originaux de Physiologie comparée. I. Insectes. Digestion, Métamorphoses. 252 pp., 5 pls. Paris. Schindler, E. 1878. Beitrage zur Kenntniss der Malpighi’schen Gefasse der Insecten. Zeits. wiss. Zool., bd. 30, pp. 587-660, taf. 38-40. Krukenberg, C. F. W. 1880. Versuche zur vergleichenden Physiologie der Verdauung und vergleichende physiologische Beitrage zur Kenntnis der Verdauungsvorgange. Unters. phys. Inst. Univ. Heidelberg. Frenzel, J. 1882. Ueber Bau und Thatigkeit des Verdauungskanals der Larve des Tenebrio molitor mit Berticksichtigung anderer Arthro- poden. Berl. ent. Zeits., bd. 26, pp. 267-316, taf. 5.* Leydig, F. 1883. Untersuchungen zur Anatomie und Histologie der Thiere. 174 pp., 8 taf. Bonn. 430 ENTOMOLOGY Metschnikoff, E. 1883. Untersuchungen tiber die intrazellulare Verdau- ung bei wirbellosen Tieren. Arb. zool. Inst. Wien, bd. 5, pp. 141- TOSM ute : Schiemenz, P. 1883. Ueber das Herkommen des Futtersaftes und die Speicheldriisen der Biene nebst einem Anhange itber das Riech- organ. Zeits. wiss. Zool., bd. 38, pp. 71-135, taf. 5-7. Locy, W. A. 1884. Anatomy and Physiology of the family Nepide. Amer. Nat., vol. 18, pp. 250-255, 353-367, pls. 9-12. Witlaczil, E. 1885. Zur Morphologie und Anatomie der Cocciden. Zeits. wiss. Zool., bd. 43, pp. 149-174, taf. 5. Frenzel, J. 1886. Einiges tiber den Mitteldarm der Insekten, sowie tber Epithelregeneration. Archiv mikr. Anat., bd. 26, pp. 229-306, taf. 7-9. Kniippel, A. 1886. Ueber Speicheldriisen von Insecten. Archiv Naturg., jhg. 52, bd. 1, pp. 269-303, taf. 13, 14. Cholodkovsky, N. 1887. Sur la morphologie de l’appareil urinaire des Lépidoptéres. Archiv. Biol., t. 6, pp. 497-514, pl. 17. Faussek, V. 1887. Beitrage zur Histologie des Darmkanals der Insekten. Zeits. wiss. Zool., bd. 45, pp. 604-712, taf. 36. Kowalevsky, A. 1887. Beitrage zur Kenntnis der nachembryonalen Ent- wicklung der Musciden. Zeits. wiss. Zool., bd. 45, pp. 542-594, taf. 26-30. Schneider, A. 1887. Ueber den Darmcanal der Arthropoden. Zool. Beitr. von A. Schneider, bd. 2, pp. 82-96, taf. 8-10. Emery, C. 1888. Ueber den sogenannten Kaumagen einiger Ameisen. Zeits. wiss. Zool., bd. 46, pp. 378-412, taf. 27-20. Macloskie, G. 1888. The Poison Apparatus of the Mosquito. Amer. Nat., vol. 22, pp. 884-888, 2 figs. Blanc, L. 1889. Etude sur la sécrétion de la soie et sur la structure du brin et de la bave dans le Bombyx mori. 56 pp., 4 pls. Lyon. Kowalevsky, A. 1889. Ein Beitrag zur Kenntnis der Exkretionsorgane. Biol. Centralb., bd. 9, pp. 33-47, 65-76, 127-128. Van Gehuchten, A. 1890. Recherches histologiques sur l'appareil digestif de la larve de la Ptychoptera contaminata, I Part. Etude du revetement épithélial et recherches sur la sécrétion. La Cellule, t. 6, pp. 183-201, pls. 1-6. Gilson, G. 1890, 1893. Recherches sur les cellules sécrétantes. La soie et les appareils séricigénes. I. Lepidoptéres; II. Trichoptéres. La Cellule, t. 6, pp. 115-182, pls. 1-3; t. 10, pp. 37-63, pl. 4. Blanc, L. 1891. La téte du Bombyx mori a l'état larvaire, anatomie et physiologie. Trav. Lab. Etud. Soie, 1889-1890, 180 pp., 95 figs- Lyon. Wheeler, W. M. 1893. The primitive number of Malpighian vessels in Insects. Psyche, vol. 6, pp. 457-460, 485-486, 497-408, 509-510, 539-541, 545-547, 501-564. LITERATURE 43! Bordas, L. 1895. Appareil glandulaire des Hymeénoptéres. (Glandes salivaires, tube digestif, tubes de Malpighi et glandes venimeuses. ) 262 pp., 11 pls. Paris. Cuénot, L. 1895. Etudes physiologiques sur les Orthoptéres. Arch. Biol., t. 14, pp. 203-341, pls. 12, 13. Bordas, L. 1897. L’appareil digestif des Orthopteres. Ann. Se. nat. Zool., sér. 8, t. 5, pp. 1-208, pls. I-12. Needham, J. G. 1897. The digestive epithelium of dragon fly nymphs. Zool. Bull., vol. 1, pp. 103-113, figs. I-Io. CIRCULATORY SYSTEM f Newport, G. 1839. Insecta. Todd’s Cyclopedia Anat. Phys., vol. 2, pp. 853-094, figs. 320-439. Newport, G. 1845. On the Structure and Development of the Blood. Ann. Mag. Nat. Hist., vol. 15, pp. 281-284. Verloren, M. C. 1847. [Mémoire sur la circulation dans les insectes.] Mém. Acad. roy. Belgique, t. 19, 93 pp., 7 pls. Blanchard, E. 1848. De la circulation dans les insectes. Ann. Sc. nat. Zool., sér. 3, t. 9, pp. 359-308, 5 pls. Leydig, F. 1851. Anatomisches und Histologisches uber die Larve von Corethra plumicornis. Zeits. wiss. Zool., bd. 3, pp. 435-451, taf. 16. Scheiber, S. H. 1860. Vergleichende Anatomie und Physiologie der CEstriden-Larven. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 41, pp. 409-496, 2 taf. Landois, H. 1864. Beobachtungen iiber das Blut der Insekten. Zeits. wiss. Zool., bd. 14, pp. 55-70, 3 taf. Graber, V. 1871. Ueber die Blutkdrperchen der Insekten. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 64, pp. 9-44. Moseley, H. N. 1871. On the circulation in the wings of Blatta orientalis and other insects, and on a new method of injecting the vessels of insects. Quart. Journ. Micr. Sc., vol. 11 (n. s.), pp. 389-395, iP iol Graber, V. 1873. Ueber den propulsatorischen Apparat der Insekten. Archiv mikr. Anat., bd. 9, pp. 129-106, 3 taf. Graber, V. 1873. Ueber die Blutkorperchen der Insekten. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 64 (1871), pp. 9-44. Graber, V. 1876. Ueber den pulsierenden Bauchsinus der Insekten. Ar- chiv mikr. Anat., bd. 12, pp. 575-582, 1 taf. Dogiel, J. 1877. Anatomie und Physiologie des Herzens der Larve von Corethra plumicornis. Mém. Acad. St. Pétersbourg, sér. 7, t. 24, 37 pp., 2 pls. Separate, Leipzig. Voss. Jaworovski, A. 1879. Ueber die Entwicklung des Riickengefasses und speziell der Muskulatur bei Chironomus und einigen anderen In- sekten. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 80, pp. 238-258. 432 ENTOMOLOGY Plateau, F. 1879. Communication préliminaire sur les mouvements et linnervation de l’organe central de la circulation chez les animaux articulés. Bull. Acad. roy. Belgique, sér. 2, t. 46, pp. 203-212. Zimmermann, 0. 1880. Ueber eine eigenthitmliche Bildung des Rutcken- gefiisses bei einigen Ephemeridenlarven. Zeits. wiss. Zool., bd. 34, pp. 404-406, figs. 1-4. Burgess, E. 1881. Note on the aorta in lepidopterous insects. Proc. Bost. Soc. Nat. Hist., vol: 21, pp. 153-156, figs. 1-5. Vayssiére, A. 1882. Recherches sur l’organisation des larves des Ephe- mérines. Ann. Sc. nat. Zool., sér. 6, t. 13, pp. I-137, pls. I-IT. Viallanes, H. 1882. Recherches sur l’histologie des Insectes, et sur les phénomeénes histologiques qui accompagnent le développement post-embryonnaire de ces animaux. Ann. Sc. nat. Zool., sér. 6, t. 14, pp. 1-348, 4 pls. Bibl. Ecole, bd. 26, 348 pp., 18 pls. Creutzburg, N. 1885. Ueber den Kreislauf der Ephemerenlarven. Zool. Anz., jhg. 8, pp.’ 246-248. Poletajewa, O. 1886. Du cceur des insectes. Zool. Anz., jhg. 9, pp. 13-15. Von Wielowiejski, H. R. 1886. Ueber das Blutgewebe der Insekten. Zeits. wiss. Zool., bd. 43, pp. 512-536. Dewitz, H. 1889. Eigenthatige Schwimmbewegung der Blutkorperchen der Gliederthiere. Zool. Anz., jhg. 12, pp. 457-464, I fig. Kowalevsky, A. 1889. Ein Beitrag zur Kenntnis der Excretionsorgane. Biol. Centralb., bd. 9, pp. 33-47, 65-76, 127-128. Schiffer, C. 1889. Beitrage zur Histologie der Insekten. II. Ueber Blutbildungsherde bei Insektenlarven. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 626-636, taf. 30. Lankester, E. R. 1893. Note on the Celom and Vascular System of Mollusca and Arthropoda. Quart. Journ. Micr. Sc., vol. 34 (n. s.), PP. 427-432. Pawlowa, M. 1895. Ueber ampullenartige Blutcirculationsorgane im Kopfe verschiedener Orthopteren. Zool. Anz., jhg. 18, pp. 7-13, I fig. FAT BODY Dufour, L. 1826. Recherches anatomiques sur les Carabiques et sur plu- sieurs autres Insectes Coléoptéres. Du tissu adipeux splanch- nique. Ann. Sc. nat. Zool., t. 8, pp. 29-35. Meyer, H. 1848. Ueber die Entwicklung des Fettk6rpers, der Tracheen und der keimbereitenden Geschlechtstheile bei den Lepidopteren. Zeits. wiss. Zool., bd. 1, pp. 175-197, 4 taf. Fabre, J. H. 1863. Etude sur le rdle du tissu adipeux dans la sécrétion urinaire chez les Insectes. Ann. Sc. nat. Zool., sér. 4, t. 19, pp. 351-382. Landois, L. 1865. Ueber die Funktion des Fettkérpers. Zeits. wiss. Zool., bd. 15, pp. 371-372. LITERATURE 433 Schultze, M. 1865. Zur Kenntniss der Leuchtorgane von Lampyris splendidula. Archiv mikr. Anat., bd. 1, pp. 124-137, taf. 5, 6. Gadeau de Kerville, H. 1881, 1887. Les insectes phosphorescents. T. 1, Bcepp.,4 pls. >t. 2) 135, pp; Rouen.* Von Wielowiejski, H. R. 1882. Studien uber Lampyriden. Zeits. wiss. Zool., bd. 37, pp. 354-428, taf. 23, 24. Von Wielowiejski, H. 1883. Ueber den Fettk6rper von Corethra plumi- cornis und seine Entwicklung. Zool. Anz., jhg. 6, pp. 318-322. Emery, C. 1884. Untersuchungen tiber Luciola italica L. Zeits. wiss. Zool., bd. 40, pp. 338-355, taf. 10. Emery, C. 1885. La luce della Luciola italica osservata con microscopio. Bull. Soc. Ent. Ital., anno 17, pp. 351-355, tav. 5. Dubois, R. 1886. Contribution a l’étude de la production de la lumiére par les étres vivants. Les Elatérides lumineux. Bull. Soc. zool. France, ann. II, pp. 1-275, pls. I-9. Heinemann, C. 1886. Zur Anatomie und Physiologie der Leuchtorgane mexikanischer Cucuyo’s. Archiv mikr. Anat., bd. 27, pp. 296-382. Von Wielowiejski, H. R. 1886. Ueber das Blutgewebe der Insekten. Zeits. wiss. Zool., bd. 43, pp. 512-536. Schaffer, C. 1889. JBeitrage zur Histologie der Insekten. H. Ueber Blutbildungsherde bei Insektenlarven. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 626-636, taf. 30. Von Wielowiejski, H. R. 1889. Beitrage zur Kenntnis der Leuchtorgane der Insecten. Zool. Anz., jhg. 12, pp. 594-600. Wheeler, W. M. 1892. Concerning the “blood tissue” of the Insecta. Psyche, vol. 6, pp. 216-220, 233-236, 253-258, pl. 7. Cuénot, L. 1895. Etudes physiologiques sur les Orthoptéres. Arch. Biol., t. 14, pp. 203-341, pls. 12, 13. Schmidt, P. 1895. On the Luminosity of Midges (Chironomide). Ann. Mag. Nat. Hist., ser. 6, vol. 15, pp. 133-141. Trans. from Zool. ‘Jahrb., Abth. Syst., etc., bd. 8, pp. 58-66, 1894. | RESPIRATORY SYSTEM Dufour, L. 1825-60. [Many papers on respiratory system.] Ann. Sc. nat. Zool. 3 Dutrochet, R. J. H. 1833. Du mécanisme de la respiration des Insectes. Ann. Sc. nat. Zool., t. 28, pp. 31-44. 1838. Mém. Acad. Sc. Paris, t. 14, pp. 81-93. Newport, G. 1836. On the Respiration of Insects. Phil. Trans. Roy. Soc. London, vol. 126, pp. 529-566. Grube, A. E. 1844. Beschreibung einer auffallenden an Siisswasser- schwammen lebenden Larve. (Sisyra.) Archiv Naturg., jhg. 9, PP. 331-337, figs. Newport, G. 1844. On the existence of Branchie in the perfect State of a Neuropterous Insect, Pteronarcys regalis Newm. and other spe- cies of the same genus. Ann. Mag. Nat. Hist., vol. 13, pp. 21-25. 29 434 ENTOMOLOGY Platner, E. A. 1844. Mittheilungen iiber die Respirationsorgane und die Haut der Seidenraupen. Miiller’s Archiv Anat. Phys., pp. 38-49, figs. Dufour, L. 1849. Des divers modes de respiration aquatique dans les insectes. Compt. rend. Acad. Sc., t. 20, pp. 763-770. 1850. Trans. Ann. Mag. Nat. Hist., ser. 2, vol. 6, pp. 112-118. Newport, G. 1851. On the Formation and the Use of the Airsacs and dilated Trachez in Insects. Trans. Linn. Soc. Zool., vol. 20, pp. 419-423. Newport, G. 1851. On the Anatomy and Affinities of Pteronarcys regalis Newm., etc. Trans. Linn. Soc. Zool., vol. 20, pp. 425-453, I pl. Dufour, L. 1852. Etudes anatomiques et physiologiques et observations sur les larves des Libellules. Ann. Sc. nat. Zool., sér. 3, t. 17, pp. 65-110, 3 pls. Hagen, H. A. 1853. Léon Dufour tiber die Larven der Libellen mit Berticksichtigung der fritheren Arbeiten. (Ueber Respiration der Insecten.) Stett. ent. Zeit., bd. 14, pp. 98-106, 237-238, 260-270, 311-325, 334-346. Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure of the Organs of Breathing in Invertebrate Ani- mals. Trans. Ann. Mag. Nat. Hist., ser. 2, vols. 12-10, 17 pls. Barlow, W. F. 1855. Observations of the Respiratory Movements of In- sects. Phil. Trans. Roy. Soc. London, vol. 145, pp. 139-148. Lubbock, J. 1860. On the Distribution of the Trachee in Insects. Trans. Linn. Soc. Zool., vol. 23, pp. 23-50, pl. 4. Rathke, H. 1861. Anatomisch-physiologische Untersuchungen tiber den Athmungsprocess der Insecten. Schrift, phys.-oek. Gesell. Kon- igsberg, jhg. I, pp. 99-138, taf. 1. Scheiber, S. H. 1862. Vergleichende Anatomie und Physiologie der (Estriden-Larven. Respirationssystem. Sitzb. Akad. Wiss. Wien, math.-naturw. Cl., bd. 45, pp. 7-68, 3 taf. Reinhard, H. 1865. Zur Entwicklungsgeschichte des Tracheensystems der Hymenopteren mit besonderer Beziehung auf dessen morpholo- gische Bedeutung. Berl. ent. Zeits., jhg. 9, pp. 187-218, taf. I, 2. Landois, H., und Thelen, W. 1867. Der Tracheenverschluss bei den In- sekten. Zeits. wiss. Zool., bd. 17, pp. 187-214, 1 taf. Oustalet, E. 1869. Note sur la respiration chez les nymphes des Libel- lules. Ann. Sc. nat. Zool., sér. 5, t. II, pp. 370-386, 3 pls. Pouchet, G. 1872. Développement du systéme trachéen de l’Anophele (Corethra plumicornis). Archiv. Zool. expér., t. I, pp. 217-232, 1 fig. Gerstacker, A. 1874. Ueber das Vorkommen von Tracheenkiemen bei ausgebildeten Insecten. Zeits. wiss. Zool., bd. 24, pp. 204-252, I tate Packard, A. S. 1874. On the Distribution and Primitive Number of Spiracles in Insects. Amer. Nat., vol. 8, pp. 531-534. LITERATURE 435 Palmén, J. A. 1877. Zur Morphologie des Tracheensystems. 10-+ 149 Dpsr2) tate klelsinefors. Sharp, D. 1877. Observations on the Respiratory Action of the Carnivo- rous Water Beetles (Dytiscide). Journ. Linn. Soc. Zool., vol. 13, pp. 161-183. Haller, G. 1878. Kleinere Bruchstiicke zur vergleichenden Anatomie der Arthropoden. J. Ueber das Atmungsorgan der Stechmiucken- larven. Archiv Nature., jhg. 44, bd. I, pp. 91-101, taf. 2. Hagen, H. A. 1880. Beitrag zur Kenntnis des Tracheensystems der Libel- len-Larven. Zool. Anz., jhg. 3, pp. 157-161. Hagen, H. A. 1880. Kiemeniiberreste bei einer Libelle; glatte Muskel- fasern bei Insecten. Zool. Anz., jhg. 3, pp. 304-305. Poletajew, O. 1880. Quelques mots sur les organes respiratoires des lar- ves des Odonates. Horz Soc. Ent. Ross., t. 15, pp. 436-452, 2 pls. Viallanes, H. 1880. Sur l’appareil respiratoire et circulatoire de quelques larves de Diptéres. Compt. rend. Acad. Sc., t. 90, pp. 1180-1182. Krancher, 0. 1881. Der Bau der Stigmen bei den Insekten. Zeits. wiss. Zool., bd. 35, pp. 505-574, taf. 28, 20. Vayssiére, A. 1882. Recherches sur l’organisation des larves des Ephé- merines. Ann. Sc. nat. Zool., sér. 6, t. 13, pp. I-137, pls. I-11. Macloskie, G. 1883. Pneumatic Functions of Insects. Psyche, vol. 3, pp. 375-378. Macloskie, G. 1884. The Structure of the Trachee of Insects. Amer. Nat., vol. 18, pp. 567-573, figs. 1-4. Plateau, F. 1884. Recherches expérimentales sur les mouvements res- piratoires des Insectes. Mem. Acad. roy. Belgique, t. 45, 219 pp., 7 pls., 56 figs. Packard, A. S. 1886. On the Nature and Origin of the so-called “ Spiral Thread” of Trachee. Amer. Nat., vol. 20, pp. 438-442, figs. I-3. Comstock, J. H. 1887. Note on Respiration of Aquatic Bugs. Amer. Nat., vol. 21, pp. 577-578. Raschke, E. W. 1887. Die Larve von Culex nemorosus. Archiv Naturg., jideai53, bd) T, pp. 133-163) tak. 5, 6: Schmidt-Schwedt, E. 1887. Ueber Athmung der Larven und Puppen von Donacia crassipes. Berlin. ent. Zeits., bd. 31, pp. 325-334, tate 5p: Vogler, C. 1887. Die Tracheenkiemen der Simulien-Puppen. Mitt. schweiz. ent. Gesell., bd. 7, pp. 277-282. Dewitz, H. 1888. Entnehmen die Larven der Donacien vermittelst Stig- men oder Athemrohren den Luftraumen der Pflanzen die sauer- stoffhaltige Luft? Berl. ent. Zeits., bd. 32, pp. 5-6, figs. I, 2. Haase, E. 1889. Die Abdominalanhange der Insekten mit Beriticksichti- gung der Myriopoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. TANTS. Cajal, S. R. 1890. Coloration par la méthode de Golgi des terminaisons des trachées et des nerfs dans les muscles des ailes des insectes. Zeits. wiss. Mikr., bd. 7, pp. 332-342, taf. 2, figs. 1-3. 430 ENTOMOLOGY Dewitz, H. 1890. Einige Beobachtungen, betreffend das geschlossene Tracheensystem bei Insectenlarven. Zool. Anz., jhg. 13, pp. 500- 504, 525-531. Von Wistinghausen, C. 1890. Ueber Tracheenendigungen in den Sericte- rien der Raupen. Zeits. wiss. Zool., bd. 49, pp. 565-582, taf. 27.* Miall, L. C. 1891. Some Difficulties in the Life of Aquatic Insects. Na- ture, vol. 44, pp. 457-462. Stokes, A. C. 1893. The Structure of Insect Trachez, with Special Ref- erence to those of Zaitha fluminea. Science, vol. 21, pp. 44-46, figs. I-7. Miall, L. C. 1895, 1903. The Natural History of Aquatic Insects. Ir + 395 pp., 116 figs. London and New York. Macmillan & Co. Sadones, J. 1895. L’appareil digestif et respiratoire larvaire des Odo- nates. La Cellule, t. 11, pp. 271-325, pls. 1-3. Gilson, G., and Sadones, J. 1896. The Larval Gills of the Odonata. Journ. Linn. Soc. Zool., vol. 25, pp. 413-418, figs. I-3. Holmgren, E. 1896. Ueber das respiratorische Epithel der Tracheen bei Raupen. Festsk. Lilljeborg, Upsala, pp. 79-06, taf. 5, 6. REPRODUCTIVE, SYSLEM Dufour, L. 1824-60. [Many papers on reproductive system.] Ann. Se. nat. Zool. Dutrochet, R. J. H. 1833. Observations sur les organes de la génération chez les Pucerons. Ann. Sc. nat. Zool., t. 30, pp. 204-2009. Von Siebold, C. T. E. 1836. Ueber die Spermatozoen der Crustaceen, In- secten, Gasteropoden und einiger andern wirbellosen Thiere. Miller's Archiv Anat. Phys., pp. 15-52, 2 taf. Von Siebold, C. T. E. 1836. Fernerer Beobachtungen tiber die Spermato- zoen der wirbellosen Thiere. Miiller’s Archiv Anat. Phys., p. 2227 Os Pes ol Aso untae Doyére, L. 1837. Observations anatomiques sur les Organes de la généra- tion chez la Cigale femelle. Ann. Sc. nat. Zool., t. 7, pp. 200-206, figs. Von Siebold, C. T. E. 1838. Ueber die weiblichen Geschlechtsorgane der Tachinen. Archiv Naturg., jhg. 4, pp. 191-201. Loew, H. 1841. Beitrag zur anatomischen Kenntniss der inneren Ge- schlechtstheile der zweifliigligen Insecten. Germar’s Zeits. Ent., bd. 3, pp. 386-406, I taf. Von Siebold, C. T. E. 1843. Ueber das Receptaculum seminis der Hy- menopteren Weibchen. Germar’s Zeits. Ent., bd. 4, pp. 362-388, Tete Stein, F. 1847. Vergleichende Anatomie und Physiologie der Insecten. I. Monographie. Ueber die Geschlechts-Organe und den Bau des Hinterleibes bei den weiblichen Kafern. 8+ 139 pp., 9 taf. 3erlin. LITERATURE 437 Brauer, F. 1855. Beitrage zur Kenntniss des inneren Baues und der Verwandlung der Neuropteren. Verh. zool.-bot. Ver. Wien, bd. 5, pp. 700-726, 5 taf. Kolliker, A. 1856. Physiologische Studien uber die Samenflussigkeit. Zeits. wiss. Zool., bd. 7, pp. 201-272, 1 taf. Huxley, T. H. 1858-59. On the Agamic Reproduction and Morphology of Aphis. Trans. Linn. Soc. Zool., vol. 22, pp. 193-236, 5 pls. Lubbock, J. 1859. On the Ova and Pseudova of Insects. Phil. Trans. Roy. Soc. London, vol. 149, pp. 341-369, pls. 16-18. Landois, H. 1863. Ueber die Verbindung der Hoden mit dem Rtckenge- fass bei den Insekten. Zeits. wiss. Zool., bd. 13, pp. 316-318, 1 taf. Claus, C. 1864. Beobachtungen tiber die Bildung des Insekteneies. Zeits. wiss. Zool., bd. 14, pp. 42-54, I taf. Pagenstecher, H. A. 1864. Die ungeschlechtliche Vermehrung der Flie- genlarven. Zeits. wiss. Zool., bd. 14, pp. 400-416, 2 taf. Wagner, N. 1865. Ueber die viviparen Gallmtickenlarven. Zeits. wiss. Zool., bd. 15, pp. 106-117. Bessels, C. 1867. Studien tiber die Entwicklung der Sexualdrtisen bei den Lepidopteren. Zeits. wiss. Zool., bd. 17, pp. 545-564, 3 taf. Leydig, F. 1867. Der Eierstock und die Samentasche der Insekten. Nova Acta Acad. Leop.-Carol., bd. 33, 88 pp., 5 taf. Biitschli, O. 1871. Nahere Mittheilungen tiber die Entwicklung und den Bau der Samenfaden der Insecten. Zeits. wiss. Zool., bd. 21, pp. 526-534, taf. 40, 41. Nusbaum, J. 1882. Zur Entwickelungsgeschichte der Ausftihrungse‘inis- der Sexualdrtisen bei den Insecten. Zool. Anz., jhg. 5, pp. 637- 643. Palmén, J. A. 1883. Zur vergleichenden Anatomie der Ausfiihrungsgange der Sexualorgane bei den Insekten. Vorlaufige Mittheilung. Morph. Jahrb., bd. 9, pp. 169-176. Will, L. 1883. Zur Bildung des Eies und des Blastoderms bei den vivi- paren Aphiden. Arbeit. zool.-zoot. Inst. Univ. Wurzburg, bd. 6, pp. 217-258, taf. 16. Palmén, J. A. 1884. Ueber paarige Ausfiihrungsgange der Geschlechts- organe bei Insecten. Ein morphologische Untersuchung. 108 pp., 5 taf. Helsingfors. Gilson, G. 1885. Etude comparée de la spermatogénése chez les Arthro- podes. La Cellule, t. 1, pp. 7-188, pls. 1-8.* Schneider, A. 1885. Die Entwicklung der Geschlechtsorgane der Insecten. Zool. Beitr. von A. Schneider, bd. 1, pp. 257-300, 4 taf. Breslau. Spichardt, C. 1886. Beitrag zur Entwickelung der mannlichen Genitalien und ihrer Ausfiihrgange bei Lepidopteren. Verh. naturh. Ver Bonn, jhg. 43, pp. 1-34, taf. I. La Valette St. George. 1886, 1887. Spermatologische Beitrage. Arch. mikr Anat, bd. 27, pp, I-12) taf. 1, 2; bd. 28) pp. 113) taf. 1-4; bd. 30, pp. 426-434, taf. 25. 438 : ENTOMOLOGY Von Wielowiejski, H. R. 1886. Zur Morphologie des Insectenovariums. Zool. Anz., jhg. 9, pp. 132-139. Korschelt, E. 1887. Ueber einige interessante Vorgange bei der Bildung der Insekteneier. Zeits. wiss. Zool., bd. 45, pp. 327-397, taf. 18, Io. Nassonow, N. 1887. The Morphology of Insects of Primitive Organiza- tion. Studies Lab. Zool. Mus. Moscow, pp. 15-86, 2 pls., 68 figs. (In Russian.) Oudemans, J. T. 1888. Beitrage zur Kenntniss der Thysanura und Col- lembola. Bijdr. Dierk., pp. 147-226, taf. 1-3. Amsterdam. Bertkau, P. 1889. Beschreibung eines Zwitters von Gastropacha quercus, nebst allgemeinen Bemerkungen und einem Verzeichniss der beschriebenen Arthropodenzwitter. Archiv Naturg., jhg. 55, bd. 1, pp. 75-116, figs. 1-3.* Leydig, F. 1889. Beitrage zur Kenntniss des thierischen Eies im unbe- fruchteten Zustande. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 287-432, taf. II-17. Lowne, B. T. 1889. On the Structure and Development of the Ovaries and their Appendages in the Blowfly (Calliphora erythrocephala). Journ. Linn. Soc. Zool., vol. 20, pp. 418-442, pl. 28.* Ballowitz, E. 1890. Untersuchungen tber die Struktur der Spermato- zoen, zugleich ein Beitrag zur Lehre vom feineren Bau der kon- traktilen Elemente. Die Spermatozoen der Insekten. (1. Cole- opteren.) Zeits. wiss. Zool., bd. 50, pp. 317-407, taf. 12-15. Henking, H. 1890-92. Untersuchungen iiber die ersten Entwicklungsvor- gange in der Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-564, taf. 24-26; bd. 51, pp. 685-736, taf. 35-37; bd. 54, pp. 1-274, taf. I-12, figs. I-12. Ritter, R. 1890. Die Entwicklung der Geschlechtsorgane und des Dar- mes bei Chironomus. Zeits. wiss. Zool., bd. 50, pp. 408-427, taf. 16. Heymons, R. 1891. Die Entwicklung der weiblichen Geschlechtsorgane von Phyllodromia (Blatta) germanica L. Zeits. wiss. Zool., bd. 53, PP. 434-536, taf. 18-20. Koschewnikoff, G. 1891. Zur Anatomie der mannlichen Geschlechtsorgane der Honigbiene. Zool. Anz., jhg. 14, pp. 393-396. Ingenitzky, J. 1893. Zur Kenntnis der Begattungsorgane der Libellu- liden. Zool. Anz., jhg. 16, pp. 405-407, 2 figs. Escherich, K. 1894. Anatomische Studien uber das mannliche Genital- system der Coleopteren. Zeits. wiss. Zool., bd. 57, pp. 620-641, taf. 26, figs. I—3. Toyama, K. 1894. On the Spermatogenesis of the Silk Worm. Bull. Coll. Agr. Univ. Tokyo, vol. 2, pp. 125-157, pls. 3, 4. Verson, E. 1894. Zur Spermatogenesis bei der Seidenraupe. Zeits. wiss. Zools bd 58s pp, 303—3s) state ty. Kluge, M. H. E. 1895. Das mannliche Geschlechtsorgan von Vespa ger- manica. Archiv Naturg., jhg. 61, bd. I, pp. 159-198, taf. Io. Peytoureau, A. 1895. Contributions a l’étude de la morphologie de l’ar- mure genitale des Insectes. 248 pp., 22 pls., 43 figs. Paris. LITERATURE 439 Wilcox, E. V. 1895. Spermatogenesis of Caloptenus femur-rubrum and Cicada tibicen. Bull. Mus. Comp. Zool., vol. 27, pp. 1-32, pls. I-5.* Wilcox, E. V. 1896. Further Studies on the Spermatogenesis of Calop- tenus femur-rubrum. Bull. Mus. Comp. Zool., vol. 29, pp. 193- 202, pls. 1-3. Fenard, A. 1897. Recherches sur les organes complémentaires internes de l’appareil génital des Orthoptéres. Bull. sc. France Belgique, t.. 29, pp. 390-533, pls. 24-28. Gross, J. 1903. Untersuchungen tiber die Histologie des Insectenovari- ums. Zool. Jahrb., Abth. Anat. Ont., bd. 18, pp. 71-186, taf. 6-14.* Griinberg, K. 1903. Untersuchungen tiber die Keim- und Nahrzellen in den Hoden und Ovarien.der Lepidoptera. Zeits. wiss. Zool., bd. 74, PP. 327-305, taf. 16-18. Holmgren, N. 1903. Ueber vivipare Insecten. Zool. Jahrb., bd. 109, pp. 431-468, Io figs.* EMBRYOLOGY Rathke, H. 1844. Ueber die Eier von Gryllotalpa und ihre Entwickelung. Muller's Archiv Anat. Phys., bd. 2, pp. 27-37, figs. I-5. Meyer, G. H. 1848. Ueber Entwicklung des Fettkorpers, der Tracheen und der keimbereitenden Geschlechtstheile bei den Lepidopteren. Zeits. wiss. Zool., bd. 1, pp. 175-197, 4 taf. Leuckart, R. 1858. Die Fortpflanzung und Entwicklung der Pupiparen nach Beobachtungen an Melophagus ovinus. Abh. naturf. Gesell. Halle, bd. 4, pp. 145-226, 3 taf. Weismann, A. 1863. Die Entwicklung der Dipteren im Ei, nach Beobacht- ungen an Chironomus spec., Musca vomitoria und Pulex canis. Zeits. wiss. Zool., bd. 13, pp. 107-220, 7 taf. Separate, 1864, 263 pp., 14 taf. Metschnikoff, E. 1866. Embryologische Studien an Insecten. Zeits. wiss. Zool., bd. 16, pp. 389-500, 10 taf. Brandt, A. 1869. Beitrage zur Entwicklungsgeschichte der Libelluliden und Hemipteren. Mém.. Acad. St. Pétersbourg, sér. 7, t. 13, pp. 1335.3) Ds. Melnikow, N. 1869. Beitrage zur Embryonalentwicklung der Insekten. Archiv Naturg., jhg. 35, bd. 1, pp. 136-180, 4 taf. Biitschli, O. 1870. Zur Entwicklungsgeschichte der Biene. Zeits. wiss. Zool., bd. 20, pp. 519-564, taf. 24-27. Kowalevsky, A. 1871. Embryologische Studien an Witrmern und Ar- thropoden. Mém. Acad. St. Pétersbourg, sér. 7, t. 16, pp. I-70, 12 pls. Dohrn, A. 1875. Notizen zur Kenntniss der Insectenentwicklung. Zeits. wiss. Zool., bd. 26, pp. 112-138. Hatschek, B. 1877. Beitrage zur Entwicklungsgeschichte der Lepidop- teren. Jenais. Zeits. Naturw., bd. 11, 38 pp., 3 taf., 2 figs. 440 ENTOMOLOGY Bobretzky, N. 1878. Ueber die Bildung des Blastoderms und der Keim- blatter bei den Insecten. Zeits. wiss. Zool., bd. 31, pp. 195-215, (ei, WL, Korotneff, A. 1883. Entwicklung des Herzens bei Gryllotalpa. Zool. Anz., jhg. 6, pp. 687-690, figs. I, 2. Packard, A. S. 1883. The Embryological Development of the Locust. Third Rept. U. S. Ent. Comm., pp. 263-285, pls. 16-21, figs. 10-11. Washington. Will, L. 1883. Zur Bildung des Eies und des Blastoderms bei den vivi- paren Aphiden. Arbeit. zool.-zoot. Inst. Univ. Wiirzburg, bd. 6, pp. 217-258, taf. 16. Ayers, H. 1884. On the Development of Cécanthus niveus and its Para- site Teleas. Mem. Bost. Soc. Nat. Hist., vol. 3, pp. 225-281, pls. 18-25, figs. I-41.* Patten, W. 1884. The Development of Phryganids, with a Preliminary Note on the Development of Blatta germanica. Quart. Journ. Micr. Sc., vol. 24 (n. s.), pp. 549-602, pls. 36a, b; ¢. Witlaczil, E. 1884. Entwicklungsgeschichte der Aphiden. Zeits. wiss. Zool., bd. 40, pp. 559-696, taf. 28-34.* Korotneff, A. 1885. Die Embryologie der Gryllotalpa. Zeits. wiss. Zool., bd. 41, pp. 570-604, taf. 29-31. Schneider, A. 1885. Ueber die Entwicklung der Geschlechtsorgane der Insecten. Zool. Beitr. von A. Schneider, bd. 1, pp. 257-300, 4 tat ~Breslaw: Blochmann, F. 1887. Ueber die Ruichtungsk6rper bei Insecteneiern. Morph. Jahrb., bd. 12, pp. 544-574, taf. 26, 27. Biitschli, O. 1888. Bemerkungen uber die Entwicklungsgeschichte von Musca. Morph. Jahrb., bd. 14, pp. 170-174, 3 figs. Cholodkovsky, N. 1888. Ueber die Bildung des Entoderms bei Blatta germanica. Zool. Anz., jhg. 11, pp. 163-166, figs. 1, 2. Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. Morph. Jahrb., bd. 13, pp. 586-615, taf. 25, 26. Graber, V. 1888. Ueber die primare Segmentirung des Keimstreifs der Insekten. Morph. Jahrb., bd. 14, pp. 345-368, taf. 14, 15, 4 figs. Henking, H. 1888. Die ersten Entwicklungsvorgange im Fliegenei und freie Kernbildung. Zeits. wiss. Zool., bd. 46, pp. 289-336, taf. 23- 26, 3 figs. Will, L. 1888. Entwicklungsgeschichte der viviparen Aphiden. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 201-286, taf. 6-10. Cholodkovsky, N. 1889. Studien zur Entwicklungsgeschichte der Insek- ten. Zeits. wiss. Zool., bd. 48, pp. 89-100, taf. 8. Graber, V. 1889. Ueber den Bau und die phylogenetische Bedeutung der embryonalen Bauchanhange der Insekten. Biol. Centralb., jhg. 9, PP. 355-363. Heider, K. 1889. Die Embryonalentwicklung von Hydrophilus piceus L-. I. Theil. o8 pp., 13) taf, o figs. Jena: LITERATURE 441 Leydig, F. 1889. Beitrage zur Kenntniss des thierischen Eies im unbe- fruchteten Zustande. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 287-432, taf. 11-17. Nusbaum, J. 1889. Zur Frage der Segmentierung des Keimstreifens und der Bauchanhange der Insektenembryonen. Biol. Centralb., jhg. 9, pp. 516-522, fig. I. Voeltzkow, A. 1889. Entwickelung im Ei von Musca vomitoria. Arbeit. zool.-zoot. Inst. Univ. Wurzburg, bd. 9, pp. 1-48, taf. 1-4. Voeltzkow, A. 1889. Melolontha vulgaris. Ein Beitrag zur Entwickelung im Ei bei Insekten. Arbeit. zool.-zoot. Inst. Univ. Wurzburg, bd. 9, pp. 49-64, taf. 5. Wheeler, W. M. 1889. The Embryology of Blatta germanica and Dory- phora decemlineata. Journ. Morph., vol. 3, pp. 291-386, pls. 15- 21, figs. I-16. Carriére, J. 1890. Die Entwicklung der Mauerbiene (Chalicodoma mur- aria Fabr.) im Ei. Archiv mikr. Anat., bd. 35, pp. 141-165, taf. 8, 8a. Henking, H. 1890-92. Untersuchungen tber die ersten Entwicklungsvor- gange in der Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-504, taf. 24-26; bd. 51, pp. 685-736, taf. 35-37; bd. 54, pp. 1-274, taf. 1-12, figs. I-12. Nusbaum, J. 1890. Zur Frage der Riickenbildung bei den Insektenem- bryonen. Biol. Centralb., jhg. 10, pp. 110-114. Ritter, R. 1890. Die Entwicklung der Geschlechtsorgane und des Dar- mes bei Chironomus. Zeits. wiss. Zool., bd. 50, pp. 408-427, taf. 16. Wheeler, W. M. 1890. On the Appendages of the First Abdominal Seg- ment of Embryo Insects. Trans. Wis. Acad. Sc., vol. 8, pp. 87- 140, pls. 1-3.* Cholodkowsky, N. 1891. Die Embryonalentwicklung von Phyllodromia (Blatta germanica). Mém. Acad. St. Pétersbourg, sér. 7, t. 38, 4-+ 120 pp., 6 pls., 6 figs. Graber, V. 1891. Ueber die embryonale Anlage des Blut- und Fettgewebes der Insekten. Biol. Centralb., jhg. 11, pp. 212-224. Wheeler, W. M. 1891. Neuroblasts in the Arthropod Embryo. Journ. Morph., vol. 4, pp. 337-343, I fig. Graber, V. 1892. Ueber die morphologische Bedeutung der ventralen Abdominalanhange der Insekten-Embryonen. Morph. Jahrb., bd. 17, pp. 467-482, figs. 1-6. Korschelt, E., und Heider, K. 1892. Lehrbuch der vergleichenden Ent- wicklungsgeschichte der wirbellosen Thiere. Heft 2, pp. 761-890, figs. Jena.* Trans.: 18099. M. Bernard and M. F. Woodward. Text-Book of the Embryology of Invertebrates. 12+ 441 pp., 198 figs. London, Swan Sonnenschein & Co., Ltd.; New York, The Macmillan Co.* Wheeler, W. M. 1893. A Contribution to Insect Embryology. Journ. Morph., vol. 8, pp. 1-160, pls. 1-6, figs. 1-7. 442 ENTOMOLOGY Heymons, R. 1895. Die Embryonalentwickelung von Dermapteren und Orthopteren unter besonderer Beriicksichtigung der Keimblatter- bildung. 8-+ 136 pp., 12 taf., 33 figs. Jena. Heymons, R. 1896. Grundztge der Entwickelung und des K6rperbaues von Odonaten und Ephemeriden. Anh. Abh. Akad. Wiss. Ber- lin, 66 pp., 2 taf. Heymons, R. 1897. Entwicklungsgeschichtliche Untersuchungen an Le- pisma saccharina L. Zeits. wiss. Zool., bd. 62, pp. 583-031, tat. 29, 30, 3 figs. Kulagin, N. 1897. Beitrage zur Kenntnis der Entwicklungsgeschichte von Platygaster. Zeits. wiss. Zool., bd. 63, pp. 195-235, taf. 10, I1. Claypole, A. M. 1898. The Embryology and Odgenesis of Anurida mari- tima (Guér.). Journ. Morph., vol. 14, pp. 219-300, pls. 20-25, I1 figs. Uzel, H. 1898. Studien tiber die Entwicklung der apterygoten Insecten. 6+ 58 pp., 6 taf., 5 figs. Berlin. Wilson, E. B. tg00. The Cell in Development and Inheritance. 21 -- 483 pp., 194 figs. New York and London. The Macmillan Co. POSTEMBRYONIC DEVELOPMENT. METAMORPHOSIS Fabre, J. L. 1856. Etude sur l’instinct et les métamorphoses des Sphé- giens. Ann. Sc. nat. Zool., sér. 4, t. 6, pp. 137-180. Fabre, J. L. 1857. Mémoire sur l’hypermétamorphose et les moeurs des Méloides. Ann. Sc. nat. Zool., sér. 4, t. 7, pp. 2909-365; 1 pl.; 1858, t. 9, pp. 265-276. Miiller, F. 1864. Fiir Darwin. Leipzig. Translation: Facts and Fig- ures in aid of Darwin, London, 1869. Weismann, A. 1864. Die nachembryonale Entwicklung der Musciden nach Beobachtungen an Musca vomitoria und Sarcophaga car- naria. Zeits. wiss. Zool., bd. 14, pp. 187-336. : Weismann, A. 1866. Die Metamorphose von Corethra_ plumicornis. Zeits. wiss. Zool., bd. 16, pp. 45-127, .5 taf. Trouvelot, L. 1867. The American Silk Worm. Amer. Nat., vol. I, pp. 30-38, 85-04, 145-149, 4 figs., pls. 5, 6. Brauer, F. 1869. Betrachtungen iiber die Verwandlung der Insekten im Sinne der Descendenz-Theorie. Verh. zool.-bot. Gesell. Wien, bd. 19, pp. 299-318; bd. 28 (1878), 1879, pp. 151-166. Ganin, M. 1869. Beitrage zur Kenntniss der Entwickelungsgeschichte bei den Insecten. Zeits. wiss. Zool., bd. 19, pp. 381-451, 3 taf. Chapman, T. A. 1870. On the Parasitism of Rhipiphorus paradoxus. Ann. Mag. Nat. Hist., ser. 4, vol. 5, pp. 191-198. Chapman, T. A. 1870. Some Facts towards a Life History of Rhipi- phorus paradoxus. Ann. Mag. Nat. Hist., ser. 4, vol. 6, pp. 314- 326, pl. 16. Landois, H. 1871. Beitrage zur Entwicklungsgeschichte der Schmetter- lingsfliigel in der Raupe und Puppe. Zeits. wiss. Zool., bd. 21, pp. 305-316, taf. 23. LITERATURE 443 Packard, A. S. 1873. Our Common Insects. 225 pp., 268 figs. Boston. Estes and Lauriat. Lubbock, J. 1874, 1883. On the Origin and Metamorphoses of Insects. 16+ 108 pp., 6 pls., 63 figs. London. Macmillan & Co. Ganin, M. 1876. [Materials for a Knowledge of the Postembryonal De- velopment of Insects. Warsaw.] (In Russian.) Abstracts: Amer, Nat., vol. 11, 1877, pp. 423-430; Zeits. wiss. Zool., bd. 28, 1877, pp. 386-380. Riley, C. V. 1877. On the Larval Characters and Habits of the Blister- beetles belonging to the Genera Macrobasis Lec. and Epicauta Fabr.; with Remarks on other Species of the Family Meloide. Trans. St. Louis Acad. Sc., vol. 3, pp. 544-562, figs. 35-39, pl. 5. Dewitz, H. 1878. Beitrage zur Kenntniss der postembryonalen Glied- massenbildung bei den Insecten. Zeits. wiss. Zool., bd. 30, suppl., pp. 78-105, taf. 5. Packard, A. S. 1878. Metamorphoses [of Locusts]. First Rept. U. S. Ent. Comm., pp. 279-284, pls. 1-3, figs. 19, 20. Dewitz, H. 1881. Ueber die Fltigelbildung bei Phryganiden und Lepi- dopteren. Berl. ent. Zeits., bd. 25, pp. 53-60, taf. 3, 4. Metschnikoff, E. 1883. Untersuchungen tiber die intracellulare Verdau- ung bei wirbellosen Thieren. Arb. zool. Inst. Wien, bd. 5, pp. 141-168, taf. 13, 14. Viallanes, H. 1883. Recherches sur l’histologie des Insectes et sur les phénomenes histologiques qui accompagnent le développement post-embryonnaire de ces animaux. Ann. Sc. nat. Zool., sér. 6, t. 14, 348 pp., 18 pls. Von Wielowiejsky, H. R. 1883. Ueber den Fettkorper von Corethra plumicornis und seine Entwicklung. Zool. Anz., jhg. 6, pp. 318- 322. Kowalevsky, A. 1885. Beitrage zur nachembryonalen Entwicklung der Musciden. Zool. Anz., jhg. 8, pp. 98-103, 123-128, 153-157. Schmidt, O. 1885. Metamorphose und Anatomie des mannlichen Aspidi- otus nerii. Archiv Naturg., jhg. 51, bd. 1, pp. 169-200, taf. 9, Io. Witlaczil, E. 1885. Zur Morphologie und Anatomie der Cocciden. Zeits. wiss. Zool., bd. 43, pp. 149-174, taf. 5. Kowalevsky, A. 1887. Beitrage zur Kenntniss der nachembryonalen Ent- wicklung der Musciden. Zeits. wiss. Zool., bd. 45, pp. 542-504, taf. 26-30. Van Rees, J. 1888. Beitrage zur Kenntnis der inneren Metamorphose von Musca vomitoria. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. I-134, taf. 1, 2, 14 figs. Hyatt, A., and Arms, J. M. 1890. Insecta. 23-+ 300 pp., 13 pls., 223 figs. Boston. D. C. Heath & Co.* Bugnion, E. 1891. Recherches sur le développement post-embryonnaire, l'anatomie, et les moeurs de |’Encyrtus fuscicollis. Rec. zool. suisse, t. 5, pp. 435-534, pls. 20-25. 444 ENTOMOLOGY Poulton, E. B. 1891. The External Morphology of the Lepidopterous Pupa: its Relation to that of the other Stages and to the Origin and History of Metamorphosis. Trans. Linn. Soc. Zool., ser. 2, vol. 5, pp. 245-263, pls. 26, 27. Korschelt, E., und Heider, K. 1892. Lehrbuch der vergleichenden Ent- wicklungsgeschichte der wirbellosen Thiere. Heft 2, pp. 761-890, figs. Jena.* Miall, L. C., and Hammond, A. R. 1892. The Development of the Head of Chironomus. Trans. Linn. Soc. Zool., ser. 2, vol. 5, pp. 265- 279, pls. 28-31. Pratt, H. S. 1893. Beitrage zur Kenntnis der Pupiparen. Archiv Na- turg., jhe. 59, bd. 1, pp. 151-200, taf. 6. Gonin, J. 1804. Recherches sur la métamorphose des Lépidopteres. De la formation des appendices imaginaux dans la chenille du Pieris brassicae. Bull. Soc. vaud. Sc. nat., t. 30, pp. 1-52, 5 pls. Miall, L. C. 1895. The Transformations of Insects. Nature, vol. 53, pp. 152-158. Hyatt, A.. and Arms, J. M. 1896. The Meaning of Metamorphosis. Nat. Sc., vol. 8, pp. 395-403. Kulagin, N. 1897. Beitrage zur Kenntnis der Entwicklungsgeschichte von Platygaster. Zeits. wiss. Zool., bd. 63, pp. 195-235, taf. 10, IT. Packard, A. S. 1897. Notes on the Transformations of Higher Hymen- optera. Journ. N. Y. Ent. Soc., vol. 4, pp. 155-166, figs. 1-5; vol. 5, Pp. 77-87, 109-120, figs. 6-13. : Pratt, H. S. 1897. Imaginal Discs in Insects. Psyche, vol. 8, pp. 15-30, II figs. Packard, A. S. 1898. A Text-Book of Entomology. 17+ 729 pp., 654 figs. New York and London. The Macmillan Co. Boas, J. E. V. 1899. Einige Bemerkungen tiber die Metamorphose der Insecten. Zool. Jahrb., Abth. Syst., bd. 12, pp. 385-402, taf. 20, figs. I-3. Lameere, A. 1899. La raison d’étre des métamorphoses chez les Insectes. Ann. Soc. ent. Belg., t. 43, pp. 619-636. Pérez, C. 1899. Sur la métamorphose des insectes. Bull. Soc. ent. France, pp. 398-402. Wahl, B. 1001. Ueber die Entwicklung der hypodermalen Imaginalschei- ben im Thorax und Abdomen der Larve von Eristalis Latr. Zeits. wiss. Zool., bd. 70, pp. 171-191, taf. 9, figs. 1-4. Pérez, C. 1902. Contribution a l'étude des métamorphoses. Bull. sc. France Belg., t. 37, pp. 195-427, pls. 10-12, 32 figs. Deegener, P. 1904. Die Entwicklung des Darmcanals der Insecten wahrend der Metamorphose. Zool. Jahrb., Abth. Anat. Ont., bd. 20, pp. 499-676, taf. 33-43.* Powell, P. B. 1904-05. The Development of Wings of Certain Beetles, and some Studies of the Origin of the Wings of Insects. Journ N. Y. Ent. Soc., vol. 12, pp. 237-243, pls. 11-17; vol. 13, pp. 5-22.* LITERATURE 445 AQUATIC INSECLS Dufour, L. 1849. Des divers modes de respiration aquatique dans les insectes. Compt. rend. Acad. Sc., t. 29, pp. 763-770. Ann. Mag. Nat. Hist., ser. 2, vol. 6, 1850, pp. 112-118. Dufour, L. 1852. Etudes anatomiques et physiologiques et observations sur les larves des Libellules. Ann. Sc. nat. Zool., sér. 3, t. 17, pp. 65-110, 3 pls. Hagen, H. A. 1853. Léon Dufour iiber die Larven der Libellen mit Berticksichtigung der frtitheren Arbeiten. (Ueber Respiration der Insecten.) Stett. ent. Zeit., bd. 14, pp. 98-106, 237-238, 260-270, 311-325, 334-340. Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure of the Organs of Breathing in Invertebrate Ani- mals. Ann. Mag. Nat. Hist., ser. 2, vols. 12-19, 17 pls. Oustalet, E. 1869. Note sur la respiration chez les nymphes des Libel- lules. Ann. Sc. nat. Zool., sér. 5, t. II, pp. 370-386, 3 pls. Sharp, D. 1877. Observations on the Respiratory Action of the Carniy- orous Water Beetles (Dytiscide). Journ. Linn. Soc. Zool., vol. 13, pp. 161-183. Poletajew, O. 1880. Quelques mots sur les organes respiratoires des lar- ves des Odonates. Hore Soc. Ent. Ross., t. 15, pp. 436-452, 2 pls. Vayssiére, A. 1882. Recherches sur l’organisation des larves des Ephé- Meniness Anil: Sc. nat, Zool, ser. 6, t 13; pp 1-137, pls. 101. Macloskie, G. 1883. Pneumatic Functions of Insects. Psyche, vol. 3, pp. 375-378. White, F. B. 1883. Report on the Pelagic Hemiptera. Rept. Sc. Res. Voy. H. M. S. Challenger, 1873-1876, Zoology, vol. 7, 82 pp., 3 pls. Comstock, J. H. 1887. Note on Respiration of Aquatic Bugs. Amer. Nat., vol. 21, pp. 577-578. Schwedt, E. 1887. Ueber Athmung der Larven und Puppen von Donacia crassipes. Berl. ent. Zeits., bd. 31, pp. 325-334, taf. 5b. Amans, P. C. 1888. Comparaisons des organes de la locomotion aqua- fants Ann Se nat. Zool, ser. 7) t. 6, pp. 1-164, pls. 1-6. Dewitz, H. 1888. Entnehmen die Larven der Donacien vermittelst Stig- men oder Athemrohren den Luftraumen der Pflanzen die sauer- stoffhaltige Luft? Berl. ent. Zeits., bd. 32, pp. 5-6, 2 figs. Garman, H. 1889. A Preliminary Report on the Animals of the Missis- sippi Bottoms near Quincy, Illinois, in August, 1888. Bull. IIl. St. Lab. Nat. Hist., vol. 3, pp. 123-184. Moniez, R. 1890. Acariens et Insectes marins des cOtes du Boulonnais. Rey. biol. nord France, t. 2, pp. 321, etc. Miall, L. C. 1891. Some Difficulties in the Life of Aquatic Insects. Na- ture, vol. 44, pp. 457-462. Walker, J. J. 1893. On the Genus Halobates, Esch., and other Marine Hemiptera. Ent. Mon. Mag., ser. 2, vol. 4 (29), pp. 227-232. Carpenter, G. H. 1895. Pelagic Hemiptera. Nat. Sc., vol. 7, pp. 60-61. 440 ENTOMOLOGY Hart, C. A. 1895. On the Entomology of the Illinois River and Adjacent Waters. Bull. Ill. St. Lab. Nat. Hist., vol. 4, pp. 149-273, pls. I-15. Miall, L. C. 1895, 1903. The Natural History of Aquatic Insects. 11+ 305 pp., 116 figs. London and New York. Macmillan & Co.* Sadones, J. 1895. L’appareil digestif et respiratoire larvaire des Odo- nates: Wa Cellules & 11, pp. 271-325, pls, 13: Gilson, G., and Sadones, J. 1896. The Larval Gills of the Odonata. Journ. Linn, Soc. Zool., vol. 25, pp. 413-418, figs. I-3. Comstock, J. H. 1897, 1901. Insect Life. 6-+ 349 pp., 18 pls., 206 figs. New York. D. Appleton & Co.* Needham, J. G. 1g00. Insect Drift on the Shore of Lake Michigan. Occas. Mem. Chicago Ent. Soc., vol. I, pp. 1-8, 1 fig. Needham, J. G., and Betten, C. 1901. Aquatic Insects in the Adirondacks. Bull. N. Y. St. Mus., no. 47, pp. 383-612, 36 pls., 42 figs: Needham, J. G., MacGillivray, A. D., Johannsen, 0. A., and Davis, K. C. 1903. Aquatic Insects in New York State. Bull. N. Y. St. Mus., no. 68, 321 pp., 52 pls., 26 figs.* COLOR AND COLORATION Dorfmeister, G. 1864. Ueber die Einwirkung verschiedener, wahrend den Entwicklungsperioden angewendeter Warmegrade auf die Farbung und Zeichnung der Schmetterlinge. Mitth. naturw. Ver. Steiermark, pp. 99-108, 1 taf. Landois, H. 1864. Beobachtungen tiber das Blut der Insecten. Zeits. wiss. Zool., bd. 14, pp. 55-70, taf. 7-0. Wood, T. W. 1867. Remarks on the Coloration of Chrysalides. Trans. Ent. Soc. London, ser. 3, vol. 5, Proc., pp. 99-101. ; Higgins, H. H. 1868. On the Colour-Patterns of Butterflies. Quart. Journ: Sc., vol. 5, pp. 323-329, I pl. Weismann, A. 1875. Studien zur Descendenztheorie. J. Ueber den Saison Dimorphismus der Schmetterlinge. Leipzig. Trans.: 1880-81. R. Meldola. Studies in the Theory of Descent. 554 pp., 8 pls. London. Scudder, S. H. 1877.