In the noctuid genus, Patula, the costal half of the hind wing is modified to form a large scent-gland, and in consequence the venation has been modified. The still greater distortion of the veins in the allied genus, Argida, was attributed by the author to its once having possessed a similar scent-gland, now become rudimentary by disuse. (Hampson.)

Peculiar white or orange-colored, hairy, thread-like processes have been found protruding from narrow openings near the tip of the abdomen of Arctian moths (Fig. 367), which throw off, according to J. B. Smith, “an intense odor, somewhat like the smell of laudanum.” We have perceived the same unpleasant odor emanating from the males of Spilosoma virginica and Arctia virgo, as well as Leucarctia acræa.

We are informed by C. Dury that similar but longer hairy appendages are thrust out by the male of Haploa clymene. Many glaucopid moths protrude similar glandular processes. Thus Müller tells us that on seizing a glaucopid female by the wings, nearly the whole body became enveloped in a large cloud of snow-white wool which came out of a sort of pouch on the ventral side of the abdomen.

The male of a glaucopid was seen to dart out a pair of long hollow hairy retractile filaments which in some species exceed the whole body in length. The apparatus secretes a peculiar odor, probably serving to allure the female (Nature), and certain Zygænidæ have on the inner side of the paranal lobes (Afterklappen) glands filled with a sweetly scented fluid. Smith has detected a peculiar brush of hair-like scales in a groove between the dorsal and ventral parts of the basal two segments of the abdomen of Schinia marginata (family Noctuidæ), and when removed it exhaled a laudanum-like smell.

The pupa of Citheronia regalis gives out from the end of the abdomen a scent reminding us of laudanum.

Another mode of disseminating pleasant, alluring odors is that of the males of certain moths, which bear pencils and tufts on their fore or hind legs, and in the case of an Indian butterfly on the greatly elongated palpi. Those on the legs are ordinarily concealed in cavities or furrows in the leg, and may be thrust out and expanded so as to widely diffuse their odor. Such are those of the males of Catocala (Fig. 368), which resemble an artist’s fitch brush. In Hepialus hecta, where the arrangements for protecting the tufts are quite abnormal, Bertkau has detected the cells which secrete the odorous fluid. In the male of another Hepialus (H. humuli) a peculiar scent proceeds from the curiously aborted and altered hind tibiæ. (Barrett.) In one case, that of a geometrid moth (Bapata dichroa of New Guinea), these pencils occur on all the legs. (Haase). In many species a distinct odor is perceptible when the leg bearing the pencil or tuft is crushed.

These eversible scent-glands have been supposed to be mostly restricted to the Lepidoptera, and to a single known case in the Trichoptera, but similar alluring male glands also occur in the Orthoptera (Locustidæ). H. Garman has described and figured in the cave cricket (Hadenœcus subterraneus) “a pair of white fleshy appendages protruding from slits between the terga of the 9th and 10th abdominal somites, the nature of which is not clear,” adding, “the slits through which the organs appear are situated one on each side anterior to and a little within the cerci. When fully protruded, the glands are white, cylindrical, a little tapering, and are about one-eighth of an inch long.” He believes that they are protruded during the period of sexual excitement, and suggests that “the sense of smell is certainly the one best calculated to bring the sexes together in the darkness of caves.” We had previously noticed these organs in alcoholic specimens, but supposed that they were fungous growths. On dissecting and making microscopic sections of them, the gland is, when extended (Fig. 369), seen to be a long, ensiform, sharp, band-like process, with numerous retractor muscular fibres. When at rest each gland is folded about five times, forming a bundle lying on each side of the end of the intestine. The walls are formed of a single layer of epithelium, as seen in Fig. 369, B.

In the male of the common wingless cricket, Ceuthophilus maculatus, we have discovered what appears to be a pair of scent-glands lying directly over the last abdominal ganglion. They form two large white sacs situated close together, with a short common duct which passes back and opens externally upwards by a transverse slit on the under side of the last segment of the body.

Watson, J. On the microscopical examination of plumules, etc. (Ent. Month. Mag., ii, 1865, p. 1.)

—— On certain scales of some diurnal Lepidoptera. (Mem. Lit. and Phil. Soc. Manchester, Ser. 3, ii, 1868, p. 63.)

—— On the plumules or battledore scales of Lycænidæ. (Mem. Lit. and Phil. Soc. Manchester, Ser. 3, iii, 1869, p. 128.) Further remarks, etc. (Ibid., p. 259.)

Anthony, J. Structure of battledore scales. (Month. Microsc. Journ., vii, 1872, p. 250; see also p. 200.)

Morrison, Herbert Knowles. On an appendage of the male Leucarctia acræa. (Psyche, i, pp. 21–22, October, 1874.)

Müller, Fritz. The habits of various insects. (Nature, June 11, 1874, pp. 102–103.)

—— Ueber Haarpinsel, Fitzflecke und ähnliche Gebilde auf den Flügeln männlicher Schmetterlinge. (Jena. Zeitschr. f. Naturw., 1877, xi, pp. 99–114.)

—— Beobachtungen an brasilianischen Schmetterlingen, ii. I. Die Duftschuppen der männlichen Maracujáfalter. (Kosmos, 1877, i, pp. 391–395, Figs. 5, 6.) II. Die Duftschuppen des männchens von Dione vanillæ. (Kosmos, ii, 1877, pp. 38–42, 7 Taf.)

—— As maculas sexuaes dos individuos masculinos das especies Danais erippus e D. gilippus. (Arch. Mus. Nac. Rio Janeiro, ii, 1877 (1878), pp. 25–29, 1 Pl.)

—— Die Duftschuppen der Schmetterlinge (nach dem “Kosmos” in Ent. Nachr., 1878, pp. 29–32, 109).

—— Wo hat der Moschusduft der Schwärmer seinen Sitz? (Kosmos, ii Jahrg., 1878, pp. 84, 85.)

—— Os orgaos odoriferos dos especias Epicalia acontius, Lin. e de Myscelia orsis, Dru. (Arch. Mus. Nac. Rio Janeiro, ii, 1879, pp. 31–35.)

—— Os orgaos odoriferos nas pernas de certos Lepidopteres. (Arch. Mus. Nac. Rio Janeiro, ii, 1879, pp. 37–46, 3 Pls.)

—— Os orgaos odoriferos da Antirrhœa archœa. (Arch. Mus. Nac. Rio Janeiro, iii, 1878, pp. 1–7, 1 Pl.)

—— A prega costal das Hesperideas. (Arch. Mus. Nac. Rio Janeiro, iii, 1880, pp. 41–50, 2 Pls.)

Weismann, August. Ueber Duftschuppen. (Zool. Anzeiger, i, 1878, pp. 98, 99.)

Arnhart, L. Sexundäre Geschlechtscharaktere von Acherontia atropos. (Verh. d. k. k. zool. bot. Ges. Wien, xxix, 1879, p. 54.)

Bertkau, Philipp. Duftapparat an Schmetterlingsbeinen. (Ent. Nachrichten, 1879, Jahrg., pp. 223, 224.)

—— Ueber den Duftapparat von Hepialus hecta. (Archiv f. naturg., xlviii Jahrg., 1882, pp. 363–370, Figs.; also in Biol. Centralblatt., ii Jahrg., 1882, pp. 500–502.)

—— Ergänzung (Duftvorrichtungen bei Lepidopteren). (Ent. Nachr., 1880, p. 206.)

—— Entomologische Mizellen. 1. Ueber Duftvorrichtungen einiger Schmetterlinge. (Verh. d. naturhist. Ver. d. preuss. Rheinlande und Westf., 1884, pp. 343–350.)

Reichenau, W. von. Der Duftapparat von Sphinx ligustri. (Ent. Nachr., 1880, p. 141; also Kosmos, iv Jahrg., 1880, pp. 387–390.)

Fügner, R. Duftapparat bei Sphinx ligustri. (Ent. Nachr., 1880, p. 166.)

Lelievre, Ernest. (Note in Le Naturaliste, June 1, 1880. Both sexes of Thais polyxena emit an odorous exhalation. Notes on exhalation from Spilosoma fuliginosa.)

Hall, C. G. Peculiar odor emitted by Acherontia atropos. (Entomologist, London, xvi, p. 14.)

Åurivillius, Christopher. Ueber secundäre Geschlechtscharactere nordischer Tagfalter. (Stockholm, 1880, Bihang till K. Svensk. Vet. Akad. Handl., v, pp. 56, 3 Taf.)

—— Des caractères sexuels secundaires chez les papillons diurnes. (Ent. Tidskrift, 1880, pp. 163–166.)

—— Anteckningar om några skandinaviska fjärilarter. (Ent. Tidskr., iv, Årg., 1884, pp. 33–37; Résumé (French), ibid., pp. 55–57.)

Kirby, W. F. Fans on the fore legs of Catocala fraxini. (Papilio, ii, p. 84, 1882.)

Bailey, James S. Femoral tufts or pencils of hair in certain Catocalæ. (Papilio, ii, 1882, pp. 51, 52, 146; also in Stettin Ent. Zeitung, xliii, p. 392.)

Edwards, Henry. Fans on the feet of Catocaline moths. (Papilio, ii, p. 146, 1882.)

Stretch, R. H. Anal appendages of Leucarctia acræa. (Papilio, iii, pp. 41, 42, 1883, 1 Fig.)

Weed, Clarence M. Appendages of Leucarctia. (Papilio, iii, 1883, p. 84.)

Grote, Aug. R. Appendages of Leucarctia acræa. (Papilio, iii, 1883, p. 84.)

Haase, Erich. Ueber sexuelle Charactere bei Schmetterlingen. (Zeitschr. f. Ent., Breslau, N. F., 1885, pp. 15–19, 36–44; also Ent. Nachr., xi Jahrg., pp. 332, 333.)

—— Duftapparate indo-australischer Schmetterlinge. (Corresp. Blatt. Ent. Ver. Iris, Dresden, 1886, pp. 92–107, 1 Taf.; ibid., 1887, pp. 159–178; ibid., 1888, pp. 281–336.)

—— Ueber Duftapparate bei Schmetterlingen. (Sitzgsber. Nat. Ges. Iris, Dresden, 1886, pp. 9–10; Abstr. in Journ. R. Micr. Soc., vi, pp. 969–970, 1886.)

—— Der Duftapparate von Acherontia. (Zeitschr. f. Ent., Breslau, N. F., 1887, pp. 5–6.)

—— Dufteinrichtung indischer Schmetterlinge. (Zool. Anzeiger, 1888, pp. 475–481.)

Dalla Torre, K. W. von. Die Duftapparate der Schmetterlinge. (Kosmos, 1885, ii, pp. 354–364, 410–423; Abstr. by J. B. Smith in Proc. Ent. Soc., Washington, i, pp. 38, 1888.)

Smith, John B. Cosmosoma omphale. (Entomologica Americana, i, pp. 181–185, 1886. Describes and figures cavities in under side of 2d–4th abdominal segments of male, filled with a silky substance. This may be for display to attract ♀, as the whole mass must be very conspicuous when protruded. No odor noticed.)

—— Scent organs in some Bombycid moths. (Entomologica Americana, ii, No. 4, pp. 79–80, 1886. Describes and figures long, slender, forked hairy, orange or white, eversible glands, everted from between 7th and 8th segments of abdomen of ♂ of Leucarctia acræa, Pyrrharctia isabella, Scepsis fulvicollis, and Cosmosoma omphale.)

—— [Notes on odors and odoriferous structures of various moths and a note by L. O. Howard on odor of Dynastes.] (Proc. Ent. Soc., Washington, i, pp. 40, 55, 56.)

Müller, W. Duftorgane der Phryganiden. (Archiv f. Naturgesch., 1887, Jahrg. liii, pp. 95–97.)

Pollack, W. Duftapparate der Hadena atriplicis und Litargyria. (xv Jahrb. Westphäl. Prov. Ver. Münster, 1887, p. 16.)

Patton, W. H. Scent-glands in the larva of Limacodes. (Can. Ent., 1891, xxiii, pp. 42, 43.)

Garman, H. On a singular gland possessed by the male Hadenœcus subterraneus. (Psyche, 1891, p. 105, 1 Fig.)

Barrett, C. G. Scent of the male Hepialus humuli. (Ent. Month. Mag., Ser. 2, iii, 1892, p. 217. Arises from the curiously aborted and altered hind tibiæ.)

Also the writings of Baillif, Duponchel, F. Müller, Scudder (Psyche, iii, p. 278, 1881), Burgess, Keferstein, Alpheraky, Plateau, Marshall and Nicéville, Wood-Mason, White, Hampson.

Although Malpighi was the first to discover the heart in the young silkworm, it was not until 1826 that Carus proved that there was a circulation of blood in insects, which he saw flowing along each side of the body, and coursing through the wings, antennæ, and legs of the transparent larva of Ephemera, though three years earlier Herold demonstrated that the dorsal vessel of an insect is a true heart, pulsating and impelling a current of blood towards the head. This discovery was extended by Straus-Dürckheim, who discovered the contractile and valvular structures of the heart. It is noteworthy that both Cuvier and Dufour denied that any circulation, except of air, existed in insects; and so great an anatomist as Lyonet doubted whether the dorsal vessel was a genuine heart, though he pointed out the fact that there are no arteries and veins connected with this vessel. Another French anatomist, Marcel de Serres, thought that the dorsal vessel was merely the secreting organ of the fat-body.

The so-called peritracheal circulation claimed by Blanchard and by Agassiz has been shown by McLeod to be an anatomical impossibility, the view having first been refuted by Joly in 1849.

Except the aorta-like continuation in the thorax and head which divides into two short branches, there are, with slight exceptions (p. 405), no distinct arteries, such as are to be found in the lobster and other Crustacea, and no great collective veins, such as exist in Crustacea and in Limulus. This is probably the result of a reduction by disuse in the circulatory system, since in myriopods (Julidæ and Scolopendridæ) lateral arteries are said to diverge near the ostia.

a. The heart

The heart or “dorsal vessel” is a delicate, pulsating tube, situated just under the integument of the back, in the median line of the body, and above the digestive canal. It can be partially seen without dissection in caterpillars. It is covered externally and lined within by membranes which are probably elastic; and between these two membranes extends a system of delicate muscular fibres, which generally have a circular course, but sometimes cross each other. The heart is divided by constrictions into chambers, separated by valvular folds. The internal lining membrane referred to forms the valvular folds separating the chambers. Each of these chambers has, at the anterior end, on each side, a valvular orifice (Fig. 370, ostium, i) which can be inwardly closed.

Miall and Denny thus describe the different layers of the wall of the heart of the cockroach:

“There are: (1) a transparent, structureless intima, only visible when thrown into folds; (2) a partial endocardium, of scattered, nucleated cells, which passes into the interventricular valves; (3) a muscular layer, consisting of close-set, annular, and distant, longitudinal fibres. The annular muscles are slightly interrupted at regular and frequent intervals, and are imperfectly joined along the middle line above and below, so as to indicate (what has been independently proved) that the heart arises as two half-tubes, which afterwards join along the middle. Elongate nuclei are to be seen here and there among the muscles. The adventitia (4), or connective tissue layer, is but slightly developed in the adult cockroach.”

Graber says that the heart of insects may be regarded not as an organ de novo, but only as the somewhat modified contractile dorsal vessel of the annelids, in which, however, the transverse arteries arising on each side became, with the gradual development of the tracheæ, superfluous and finally abortive. He describes it as a muscular tube composed of very delicate annular fibres, which within and without is covered by a relatively homogeneous, strong, elastic membrane.

The division into separate chambers is effected by means of a folding inwards and forwards of the entire muscular wall. “A portion of each side of the heart is first extended inwards so as very nearly to meet a corresponding portion from the opposite side, and then, being reflected backwards, forms, according to Straus (Consid., etc., p. 356), the interventricular valve which separates each chamber from that which follows it. Posteriorly to this valve, at the anterior part of each chamber, is a transverse opening or slit (Fig. 371, b), the auriculo-ventricular orifice, through which the blood passes into each chamber, and immediately behind it is a second, but much smaller, semilunar valve (c), which, like the first, is directed forwards into the chamber. It is between these two valves on each side that the blood passes into the heart, and is prevented from returning by the closing of the semilunar valve. When the blood is passing into the chamber, the interventricular valve is thrown back against the side of the cavity, but is closed when, by the contraction of the transverse fibres, the diameter of each chamber is narrowed, and the blood is forced along into the next chamber.” (Newport.)

According to Müller, there is but a single pair of ostia in Phasma, and, in the larva of Corethra, the heart is a simple, unjointed tube, not divided into chambers, and Viallanes states that, in the very young larva of Musca, there are no ostia (Kolbe). In the larva of Ptychoptera, Grobben found a short oval heart, with one pair of ostia situated in the 6th abdominal segment; a long aorta proceeds from it, the thoracic portion of which pulsates; from behind the heart arises a pulsating pouch, which connects with the hinder aorta, which does not pulsate, and ends at the base of two tracheal gills. Burmeister was able to find only four pairs of openings in the larva of Calosoma. Newport states that, while Straus figures nine chambers in Melolontha, and, consequently, eight pairs of openings, he has not been able to observe more than seven pairs of openings in Lucanus cervus. He has invariably found eight pairs of openings both in the larva and imago of Sphinx ligustri, as well as in other Lepidoptera. According to Béla-Dezso, the number of pairs of ostia corresponds to that of the pairs of stigmata.

There also occur, on each side of each chamber, two so-called pear-shaped bodies which are separated from the tubular portion of the heart itself, but, by means of muscular fibres, are united with the chamber and with their valves. These pyriform bodies appear as vesicles or cells with granular contents, besides some nuclei with nucleoli. They are of very small size. According to the measurements of Dogiel, in the larva of Corethra plumicornis, they are 0.02 to 0.1 mm. long, and 0.06 to 0.08 mm. broad. He regards these peculiar bodies as apolar nerve-cells of the heart. (Kolbe.)

Besides the venous openings of the heart which open into the pericardial region, Kowalevsky has discovered, in the heart of some Orthoptera (Caloptenus, Locusta, etc.), five pairs of openings by which the cardiac chambers receive the blood of the peri-intestinal region. Graber had divided the cœlom of insects into three regions (pericardial, peri-intestinal, and perineural regions), and hitherto only a union of the heart with the pericardial region by slit-like openings was known. These openings are symmetrically distributed on five abdominal segments; each section of the heart in this region has, therefore, four openings, which are all of a truly venous nature. These openings, called cardio-cœlomic apertures, are visible to the naked eye, being situated on conical papillæ of the walls of the heart. These papillæ pass through the outer diaphragm, and open into the peri-intestinal part of the cœlom, in the Acrydiidæ directly, in the Locustidæ through special canals. The cells of the papillæ are spongy, possessing large nuclei, and similar, as a whole, to glandular cells. (Comptes rendus, cxix, 1894.)

The mechanism by which the ostia are closed consists, according to Graber, of an ∞-shaped muscle passing around the two openings, and which, being interlaced, is sufficient to close the openings. But this is not all. The fore and hinder edge of the ostia project, leaf-like, into the cavity of the heart, and thus form, with the outer walls, two valves which, during the systole, filled with the blood rushing in, not only hermetically close the lateral openings, but also, by the simultaneous closure of the entire chamber by the circular muscles in the middle of the same, the two valves, simultaneously approaching each other, so nearly touch that they form a transverse partition wall in the chamber. But, for the last purpose, i.e. for the separation of the chambers from one another, there is a very special contrivance. In the May beetle, we find, besides a valve (Fig. 373, B, e), opening into the middle of the chambers, a large, stalked cell (d), which, in the diastole, i.e. in the expansion of the heart, hangs down free on the walls of the heart; but, in the systole or contraction, like a cork, closes the middle of the valve, but does not wholly close the cavity. He has observed, in the larva of Corethra, formal, interventricular valves, which also are not in the middle, but are separated from one another in the interlaced ends. They consist of two longitudinally membranous flaps which move against each other like two valves (Fig. 373, B, b).

“But what is the necessity for such a complicated mechanism? All the blood from behind passes into the heart, and, for its propulsion a simple muscular tube, whose circular fibres would draw together and contract it, would be thought to be sufficient. But the heart, except in some larvæ, ends posteriorly in a blind sac, and the blood can only pass into it by a series of pairs of lateral openings. Now, as regards the reception and the propulsion of the blood forwards, two modes are conceivable. The simplest way would be that the tubular heart should, along its whole length, contract or expand; that, moreover, the blood should be simultaneously sucked in through all the openings, and that then, also, the contraction, or systole, should take place in every part of the heart at the same moment. But this would, plainly, in so long and thin-walled a vessel, be highly impracticable, since, through such a manipulation, the mass of blood enclosed in the heart would be crowded together rather than really impelled forwards. Only the second case could be admissible, and that is this, that each chamber pulsates, one after another, from behind forwards. But, then, each segmental heart must be separated from the others by a valve. To make the matter wholly clear, we may observe an insect heart pulsating, and this is best seen in one of its middle chambers. This chamber expands (simply by the relaxation of its circular muscles), the ostia, also, consequently open, and a given quantity of blood is drawn in from the pericardial cavity. What now would happen after the succeeding contraction if there were no valves between? The blood would not flow forwards, but seek a way out backwards.

“But, in fact, the valve of the hinder chamber, at this time, closes itself, while, by the simultaneous expansion of the anterior ones, their door opens, and this section of the heart, at the same time, causes a sucking in of the contents of the posterior chamber. This phenomenon is repeated, in the same way, from chamber to chamber, which also acts alternately as ventricle and auricle, or by a sucking and pumping action. One is involuntarily reminded of the ingenious manipulation by which, by the alternate opening and shutting of the flood-gates, a vessel is carried along a canal.

“This wave-like motion of an insect’s heart also has the advantage that, just before a pulse-wave has reached the chambers farthest in front, the hinder ones are already prepared for the production of a second, for, as a matter of fact, often 60, and even 100, and, in very agile insects, 150, waves pass, in a single minute, through the series of chambers, which make it very difficult to follow the flowing of their waves.” (Graber.)

The propulsatory apparatus.—But the heart itself is only a part of the entire propulsatorial apparatus to which belongs the following contrivance, the nature of which has been worked out by Graber.

Under the dorsal vessel is stretched a sort of roof-like diaphragm, i.e. a membrane, arched like the dorsal wall of the hind-body which is attached, in a peculiar way, to the sides of the body. The best idea can be gained by a cross-section through the entire body (Fig. 374): H is the true dorsal vessel; S, the diaphragm. A surface view is seen at 373, C, b, where it appears as a plate with the edge regularly curved outwards on each side. Its precise mode of working is thus: from each dorsal band of the sides of the abdomen arises a pair of muscles spreading out fan-like, and extending to the heart, so that the fibres of one side pass directly over to those of the other, often splitting apart, or, between the two, extends outwards a perforated, thin web, like an elastic, fibrous sheet (Fig. 373, A, a), with numerous perforations, forming a diaphragm.

Graber has thus explained the action of the pericardial diaphragm and chamber, as freely translated by Miall and Denny: “When the alary muscles contract, they depress the diaphragm, which is arched upwards when at rest. A rush of blood towards the heart is thereby set up, and the blood streams through the perforated diaphragm into the pericardial chamber. Here it bathes a spongy or cavernous tissue (the fat-cells), which is largely supplied with air-tubes, and having been thus aerated, passes immediately forwards to the heart, entering it at the moment of diastole, which is simultaneous with the sinking of the diaphragm.”

In the cockroach, however, Miall and Denny think that the facts of structure do not altogether justify this explanation: “The fenestræ of the diaphragm are mere openings without valves. The descent of a perforated non-valvular plate can bring no pressure to bear upon the blood, for it is not contended that the alary muscles are powerful enough to change the figure of the abdominal rings.... The diaphragm appears to give mechanical support to the heart, resisting pressure from a distended alimentary canal, while the sheets of fat-cells, in addition to their proper physiological office, may equalize small local pressures, and prevent displacement. The movement of the blood towards the heart must (we think) depend, not upon the alary muscles, but upon the far more powerful muscles of the abdominal wall, and upon the pumping action of the heart itself.”

“The peculiar office,” says Graber, “performed by the heart has already been stated. It is nothing more than a regulator; than an organ for directing the blood in a determinate course in order that this may not wholly stagnate, or only be the plaything of a force acting in another way, as, for example, through that afforded by the body-cavity and the inner digestive canal. At regular intervals a portion of the blood is sucked through the same, and then by means of the anterior supply tube it is pushed onward into the head, whence it passes into the cavities of the tissues. The different conditions of tension under which the mass of blood stands in the different regions of the body then causes a farther circulation. Besides this, the blood passes through separate smaller pumping apparatuses, and through vessel-like modifications of cavities, also through hollow spaces between the muscles, as, for example, in the appendages where a regular backward and forward flow of the blood, especially in the limbs, wings, antennæ, and certain abdominal appendages takes place. Here and there may occasionally occur a narrow place where the flow of blood is obstructed by the accumulation of the blood corpuscles, causing a considerable stagnation.” (Graber.)