Chapter XXI: Part I: Morphology and Physiology (17)

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.

FIG. 368.—Scent-tufts on middle legs of _Catocala concumbens_.—After
Bailey.
]

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_.

FIG. 369.—Eversible scent-glands (_a_) of Hadenœcus, nat. size:
Kingsley, _del._; _A_, a gland outstretched, with the retractor
muscular fibres; _t_, part of the tergite. _B_, section of the
gland, showing the single layer of epithelial cells, and the
muscular fibres (_m_).—Author _del._
]

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.

LITERATURE ON ALLURING GLANDS

=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.

THE ORGANS OF CIRCULATION

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.”

FIG. 370.—Part of the heart of _Lucanus cervus_: _a_, the posterior
chambers (the anterior ones are covered by a part of the ligaments
which hold the heart in place); _i_, auriculo-ventricular openings;
_g_, _g_, the lateral muscles fixed by the prolongations _h_, _h_,
to the upper side of the abdomen.—After Straus-Dürckheim.
]

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.)

FIG. 371.—A, heart of _Lucanus cervus_: _a_, valves or chambers;
_bb_, alary muscles; _c_, supposed auricular space around the
heart. _B_, division into arteries of the end of the aorta in
larva of _Vanessa urticæ_. _C_, interior of the chamber, showing
the transverse fibres; _b_, auriculo-ventricular opening and valve
into the chambers; _c_, semilunar valve; _d_, interventricular
valve.—After Straus-Dürckheim, from Newport.
]

FIG. 372.—Heart of Belostoma.—After Locy.
]

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.)

FIG. 373.—A, part of the heart of _Dyticus marginalis_, showing the
spiral arrangement of the muscular fibres; _c_, closed, _e_, open,
valve; _a_, dorsal diaphragm with interwoven muscular fibres; _b_,
arrangement of fibres, recalling the screw-like features of the
fibres of the human heart; _d_, narrow end. _B_, diagrammatic
figure of the valvular openings, with the terminal flap (_e_), and
the cellular valve, of a May beetle; _a_, valvular opening of a
dipterous larva, with the interventricular valve (_b_). _C_,
abdomen of a mole-cricket, ventral view; _c_, the segmented heart;
_a_, aorta; _b_, segmented diaphragm under it.—After Graber.
]

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.

FIG. 374.—Diagram of transverse section of pericardial sinus of
_Ædipoda cœrulescens_: _H_, heart; _s_, septum; _m_, muscles,—the
upper suspensory, the lower alary.—After Graber, from Sharp. (See
also Fig. 377.)
]

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.)

FIG. 375.—_Libellula depressa_, opened from the back, showing the
nervous cord (_b_{1}_-_b_{3}_, thoracic, _h_{1}_-_h_{7}_, abdominal,
ganglia), also the furrow-like ventral sinus closed by a muscular
diaphragm.
]

FIG. 376.—_A_, part of the ventral furrow of _Libellula depressa_ more
highly magnified: _a_, a sternal plate (urite); _c_, the septum
stretched over it, at _s_ in a relaxed or collapsed state; _b_ and
_d_, the wing-like, sternal processes from which the muscular
bundles of the diaphragm arise. _B_, same in Acridium.
]

FIG. 377.—Diagrammatic section of the abdomen of _Acridium
tartaricum_, showing the ventral septum (_i_, _p_, _l_) contracted,
and (_i_, _k_, _l_) stretched out; _oh_, rib-like lateral processes
of the urite; _f_, ganglia; _b_, heart, with its suspensorium (_a_);
_c_, fat tissue in the pericardial tissue sinus; _d_, dorsal septum
or diaphragm contracted. _q_, extended; _g_, fat-body; _e_, muscular
part of diaphragm; _no_, expiration, _hm_, inspiration, muscle.—This
and Figs. 375, 376, after Graber.
]

=The supraspinal vessel.=—In many insects there is a ventral heart acting on the heart’s blood as an aspirator, or more correctly a ventral sinus lying on the nervous cord, and closed by a pulsating diaphragm. This was discovered by Réaumur in the larva of a fly, and by Graber in the dragon-fly and locusts (Acrydiidæ). A glance at Figs. 375 and 376 will save a long description. The ventral wall forms a furrow, and between its borders (Fig. 377, _e_) extends the diaphragm. During the contraction of the muscles—and this, here, acts from before backwards—the membrane rises up and makes a cavity for the blood, which passes backwards over the nervous cord. The dorsal and ventral sinuses together thus bring about a closed circulation.

It thus appears that the insects are well provided with the means of distribution of their nutritive fluid, and that the blood is kept continually fresh and rich in oxygen. (Graber.)

=The aorta.=—While the heart is mostly situated within the abdomen, it is continued into the thorax and the head as a simple, non-pulsating tube, called the aorta. In Sphinx the aorta, as described by Newport, begins at the anterior part of the 1st abdominal segment, where it bends downwards to pass under the metaphragma and enter the thorax; it then ascends again between the great longitudinal dorsal muscles of the wings, and passes onwards until it arrives at the posterior margin of the pronotum; it then again descends and continues its course along the upper surface of the œsophagus, with which it passes beneath the brain, in front of which and immediately above the pharynx, it divides into two branches, each of which subdivides. Newport, however, overlooked a thoracic enlargement of the aorta called by Burgess the “aortal chamber” (Fig. 310, _a_, _c_).

FIG. 378.—_A_, last three abdominal segments and bases of the three
caudal processes of _Cloëon dipterum_: _r_, dorsal vessel; _kl_,
ostia; _k_, special terminal chamber of the dorsal vessel with its
entrance _a_; _b_, blood-vessel of the left caudal process. _B_,
26th joint of the left caudal appendage from below: _b_, a portion
of the blood-vessel; _o_, orifice in the latter.—After Zimmermann,
from Sharp.
]

“In Sphinx and _Vanessa urticæ_, immediately after the aorta has
passed beneath the cerebrum, it gives off laterally two large
trunks, which are each equal in capacity to about one-third of the
main vessel. These pass one on each side of the head, and are
divided into three branches which are directed backwards, but have
not been traced farther in consequence of their extreme delicacy.
Anterior to these trunks are two smaller ones which appear to be
given to the parts of the mouth and antennæ, and nearer the median
line are two others which are the continuations of the aorta. These
pass upwards, and are lost in the integument. The whole of these
parts are so exceedingly delicate that we have not, as yet, been
able to follow them beyond their origin at the termination of the
aorta, but believe them to be continuous, with very delicate,
circulatory passages along the course of the tracheal vessels. It is
in the head alone that the aorta is divided into branches, since,
throughout its whole course from the abdomen, it is one continuous
vessel, neither giving off branches, nor possessing lateral muscles,
auricular orifices, or separate chambers.” (Newport, art. Insecta,
p. 978.)

Dogiel observed in the transparent larva of _Corethra plumicornis_ that the aorta extends only to the hinder border of the brain. Here it divides into two lamellæ, each of which independently extends farther on. One lamella is seen under the brain and under the eye, the other reaches near the eye. The lamellæ are tied to the integument by threads. At the point of division of the aorta is an opening. (Kolbe.)

True blood-vessels appear to exist in the caudal appendages of the
May-flies, as the heart appears to divide and pass directly into
them (Fig. 378). The last chamber of the heart diminishes in size at
the end of the body, and then divides into three delicate tubular
vessels which pass into the three caudal appendages, and extend to
the end of each one, along the upper side. While the valves of the
heart, in all insects, are directed anteriorly because the blood
flows from behind, in the larva of the Ephemeridæ the valves of the
last chamber of the heart are directed backwards, because from this
chamber the blood flows in the opposite direction, _i.e._ into the
caudal appendages. During the contraction of the heart, the
elongated section of the same in the last abdominal segment receives
a part of the mass of blood contained in the last chamber, which is
driven by independent contractions into the caudal appendages. These
vessels have openings before the end through which the blood enters
into the cavity of the appendages, and can also pass back, in order
to be taken up by the body cavity. It is possible that these
blood-vessels stand in direct relation to respiration. (Zimmermann,
Creutzburg, in Kolbe, p. 544.)

=The pericardial cells.=—Along the heart, on both sides, occur the
so-called pericardial cells, which differ from the fat-cells, and
also the peritracheal cells of Frenzel, and are mostly arranged in
linear series, which have a close relation to the circulation of the
blood. In the larva of Chironomus, they lie in groups; in that of
Culex, they are arranged segmentally. In caterpillars, these
pericardial cells are not situated in the region of the heart, but
are arranged linearly on the side, and form a network of granulated
cells situated between the fat-bodies. Other rows of these cells are
situated near the stigmata and the main lateral tracheæ. (Kolbe.)

According to Kowalevsky, the pericardial cells, and the
garland-shaped, cellular cord consist of cells, whose function it is
to purify the blood, and to remove the foreign or injurious matters
mingled with the blood.

FIG. 379.—Diagram of the circulatory organs in the head of the
cockroach, seen from above: _A_, ampulla; _V_, antennal vessel;
_M_, chief muscular cord; _m_, muscular band; _Bs_, wall of the
blood sinus; _am_, opening of the aorta (a); _rg_, anterior
sympathetic or visceral ganglion; _hg_, hinder visceral ganglion;
_F_, _F_, facetted eyes; _o_, vestigial ocellus; _G_, _G_, brain;
_S_, œsophagus.—After Pawlowa.
]

=Ampulla-like blood circulation in the head.=—In the head of the
cockroach occurs, according to Pawlowa, a contractile vascular sac
at the base of each antenna. The cavity has a valvular communication
with the blood space below and in front of the brain, and
muscle-fibres effect systole and diastole. Each sac is beyond doubt
an independently active part of the circulatory system. These organs
also occur in Locusta and other Acrydiidæ, and Selvatico has
described similar structures in _Bombyx mori_ and certain other
Lepidoptera.

=Pulsatile organs of the legs.=—Accessory to the circulation is a
special system of pulsatile organs in the three pairs of legs of
Nepidæ, generally situated in the tibia just below its articulation
with the femur, but in the fore legs of Ranatra, in the clasp-joint
or tarsus, just below its articulation with the tibia. First
observed by Behn (1835), Locy has studied the organ (Fig. 380) in
Corixa, Notonecta, Gerris, besides the Nepidæ. It is a whip-like
structure attached at both ends, with fibres extending upward and
backward to the integument of the leg, separate from the muscular
fibres and does not involve them in its motions, and is not affected
by the muscles themselves. “As the blood-corpuscles flow near the
pulsating body they move faster, and around the organ itself there
is a whirlpool of motion.” The beating of these organs aids the
circulation in both directions, and when the motion ceases, the
blood-currents in the legs stop; the rate of the pulsating organ is
always faster than that of the heart, and the action is automatic.

FIG. 380.—Pulsating organs in Hemiptera: _A_, Belostoma nymph, _B_,
legs of Corixa. _C_, Ranatra, adult, to show the exceptional
position of the pulsating organ in the fore legs. _D_, pulsatile
organ in tibia of Ranatra.—After Locy.
]

_b._ The blood

The blood of insects, as in other invertebrates, differs from that of the higher animals in having no red corpuscles. It is a thin fluid, a mixture of blood (serum) and chyle, usually colorless, but sometimes yellowish or reddish, which contains pale amœboid corpuscles corresponding to the white corpuscles (leucocytes) of the vertebrates, though they are relatively less numerous in the blood of insects. The yellow fluid expelled from the joints of certain beetles (Coccinella, Timarcha, and the Meloidæ) is, according to Leydig, only the serum of the blood. In phytophagous insects the blood is colored greenish by the chlorophyll set free during digestion. The blood of _Deilephila euphorbia_ is colored an intense olive-green, and that of _Cossus ligniperda_ is pale yellow. (Urech.) The blood of case-worms (Trichoptera) is greenish. In some insects it is brownish or violet. The serum is the principal bearer of the coloring material, yet Graber has shown that in certain insects the corpuscles are more or less beset with bright yellow or red fat-globules, so as to give the same hue to the blood.

=The leucocytes.=—The corpuscles are usually elongated, oval, or flattened oat-shaped, with a rounded nucleus, or are often amœbiform; and they are occasionally seen undergoing self-division. When about to die the corpuscles become amœbiform or star-shaped. (Cattaneo.) Their number varies with the developmental stage of the insect, and in larvæ increases as they grow, becoming most abundant shortly before pupation. The blood diminishes in quantity in the pupal stage, and becomes still less abundant in the imago. (Landois.) The quantity also varies with the nutrition of the insect, and after a few days’ starvation nearly all the blood is absorbed. Crystals may be obtained by evaporating a drop of the blood without pressure; they form radiating clusters of pointed needles. The freshly drawn blood is slightly alkaline. (Miall and Denny.)

The size of the corpuscles has been ascertained by Graber, who found
that the diameter of the circular blood-disks of the leaf-beetle,
_Lina populi_, is 0.006 mm.; of _Cetonia aurata_ and _Zabrus
gibbus_, 0.008 to 0.01 mm.; and those of certain Orthoptera
_(Decticus verrucivorus_, _Ephippiger vitium_ and _Œdipoda
cœrulescens_), 0.011 to 0.014 mm. The longest diameter of the
elongated corpuscles of _Carabus cancellatus_ is 0.008 mm.; of
_Gryllus campestris_, _Locusta viridissima_, _Cossus ligniperda_,
_Sphinx ligustri_ (pupa), and others, 0.008 to 0.01 mm.; of
_Caloptenus italicus_, _Saturnia pyri_, _Anax formosus_, and others,
0.011 to 0.014 mm.; of _Ephippiger vitium_, _Œdipoda cœrulescens_,
_Pezotettix mendax_, _Zabrus gibbus_, _Phryganea_, and others, 0.012
to 0.022 mm.; in _Stenobothrus donatus_ and _variabilis_, 0.012 to
0.035 mm. The largest known are those of _Melolontha vulgaris_,
which measure from 0.027 to 0.03 mm.

FIG. 381.—Blood corpuscles, or leucocytes, of insects: _A_, _a-g_, of
_Stenobothrus dorsatus_ (the same forms occur in most Orthoptera and
in other insects). _B_, _a_, leucocyte of the same insect with the
nucleus brought out by ether; _b_, another of serpentine shape. _C_,
leucocytes of the same insect after a longer stay in ether. _D_,
leucocytes of the same after being in glycerine 14 days.—After
Graber.
]

As regards the nature of the corpuscles, Graber concludes that they are more like the cells of the fat-bodies than genuine cells. That they are not true cells is shown by the fact that after remaining in their normal condition a long time they finally coalesce and form cords. After shrivelling, or after the blood has been subjected to different kinds of treatment, the nucleus is clearly brought out (Fig. 381).

Besides the blood corpuscles there have been detected in the blood round bodies which are regarded as fat-cells. They are circular, and for the most part larger than the blood corpuscles, have a sharp, even, dark outline, and an invariably circular nucleus. (Kolbe.)

The blood of Meloe, besides the amœboid corpuscles, according to
Cuénot, contains abundant fibrinogen, which forms a clot; a pigment
(uranidine), which is oxidized and precipitated when exposed to the
air; a dissolved albuminoid (hæmoxanthine), which has both a
respiratory and nutritive function; and, finally, dissolved
cantharidine.

The corpuscles arise from tissues which are very similar to the
fat-bodies, and which, at given times, separate into cells. The
position of these tissues is not always the same in different
insects. In caterpillars, they occur in the thorax, near the germs
of the wings; in the saw-flies (Lyda), in all parts of the thorax
and abdomen; in larval flies (Musca), in the end of the abdomen,
just in front of the large terminal stigmata. The place where the
blood corpuscles are formed is usually near, or in relation with,
the fat-bodies. But while the fat-bodies mostly serve as the
material for the formation of the blood-building tissues, in
caterpillars the tracheal matrix also, and, in dipterous larvæ, the
hypodermis serve this purpose. (Cæsar Schaeffer in Kolbe. See also
Wielowiejski, Ueber das Blutgewebe.)

Other substances occur in the blood of insects. Landois (1864)
demonstrated the existence of egg albumen, globulin, fibrin, and
iron in the blood of caterpillars. Poulton found that the blood of
caterpillars often contained chlorophyll and xanthophyll derived
from their food plants. A. G. Mayer has recently found that the
blood (hæmolymph) of the pupæ of Saturniidæ (_Callosamia promethea_)
contains egg albumin, globulin, fibrin, xanthophyll, and
orthophosphoric acid, and Oenslager has determined that iron,
potassium, and sodium are also present. (Mayer.)

_c._ The circulation of the blood

Every part of the body and its appendages is bathed by the blood, which circulates in the wings of insects freshly emerged from the nymph or pupal state, and even courses through the scales of Lepidoptera, as discovered by Jaeger (Isis, 1837).

In describing the mechanism of the heart we have already considered in a general way the mode of circulation of the blood.

The heart pumping the blood into the aorta, the nutritive fluid passes out and returns along each side of the body; distinct, smaller streams passing into the antennæ, the legs, wings (of certain insects), and into the abdominal appendages when they are present. All this may readily be observed in transparent aquatic insects, such as larval Ephemeræ, dragon-flies, etc., kept alive for the purpose under the microscope in the animalcule box.

Carus, in 1827, first discovered the fact of a complete circulation of the blood, in the larva of Ephemera. He saw the blood issuing in several streams from the end of the aorta in the head and returning in currents which entered the base of the antennæ and limbs in which it formed loops, and then flowing into the abdomen, entered the posterior end of the heart. Wagner (Isis, 1832) confirmed these observations, adding one of his own, that the blood flows backward in two venous currents, one at the sides of the body and intestine, and the other alongside of the heart itself, and that the blood not only entered at the end of the heart, but also at the sides of each segment, at the position of the valves discovered by Straus-Dürckheim.

Newport maintains that the course of the blood is in any part of the body, as well as in the wings, almost invariably in immediate connection with the course of the tracheæ, for the reason that “the currents of blood in the body of an insect are often in the vicinity of the great tracheal vessels, both in their longitudinal and transverse direction across the segments.”

The circulation of the blood in the wings directly after the exuviation of the nymph or pupa skin, and before they become dry, has been proved by several observers. As stated by Newport, the so-called “veins” or “nervures” of the wings consist of tracheæ lying in a hollow cavity, the peritracheal space being situated chiefly under and on each side of the trachea.

FIG. 382.—Circulation of the blood in hind wing of _Periplaneta
orientalis_: the arrows indicate the usual direction of the blood
currents.—After Moseley.
]

Newport gives the following summary of the observations of the early
observers, to which we add the observations of Moseley. “A motion of
the fluids has been seen by Carus in wings of recently developed
Libellulidæ, _Ephemera lutea_ and _E. marginata_, and _Chrysopa
perla_; among the Coleoptera, in the elytra and wings of _Lampyris
italica_ and _L. splendidula_, _Melolontha solstitialis_ and
Dytiscus.” Ehrenberg saw it in Mantis, and Wagner in the young of
_Nepa cinerea_ and _Cimex lectularius_. Carus detected a circulation
in the pupal wings of some Lepidoptera, and Bowerbank witnessed it
in a Noctuid (_Phlogophora meticulosa_); Burmeister observed it in
_Eristalis tenax_ and _E. nemorum_, and Mr. Tyrrel in _Musca
domestica_, but it has not been observed in the wings of
Hymenoptera.

Bowerbank observed that in the lower wing of _Chrysopa perla_ the
blood passes from the base of the wing along the costal,
post-costal, and externo-medial veins, outwards to the apex of the
wing, giving off smaller currents in its course, and that it returns
along the anal vein to the thorax. He found that the larger veins,
1⁄408 in. in diameter, contained tracheæ which only measured 1⁄2222
of an inch in diameter; but in others the tracheæ measured 1⁄1340,
while the cavity measured only 1⁄500 of an inch. He states, also,
that the tracheæ very rarely give off branches while passing along
the main veins, and that they lie along the canals in a tortuous
course. (Newport, art. Insecta, p. 980.)

Bowerbank, also, in his observations on the circulation in the wings
of Chrysopa, “used every endeavor to discover, if possible, whether
the blood has proper vessels, or only occupied the internal cavities
of the canals; and that he is convinced that the latter is the case,
as he could frequently perceive the particles not only surrounding
all parts of the tracheæ, and occupying the whole of the internal
diameter of the canals, but that it frequently happens that globules
experienced a momentary stoppage in their progress, occasioned by
their friction against the curved surface of the tracheæ, which
sometimes gave them a rotatory motion.”

FIG. 383.—Parts of a vein of the cockroach, showing the nerve (_n_)
by the side of the trachea (_tr_); _c_, blood corpuscles.—After
Moseley.
]

Moseley found, owing to the large size and number of the corpuscles,
that the circulation of the blood in the wings of insects is most
easily observed in the cockroach, especially the hind wings. As seen
in Moseley’s figure, the blood flows outward from the body through
the larger veins (I and II) of the front edge of the wings, which he
calls the main arteries of the wings, and more generally returns to
the body through the veins in the middle of the wing; the blood also
flows out from the body through the inner longitudinal veins (those
behind vein IV), and the blood is also seen to flow through some of
the small cross-veins. Fig. 383 shows one of the main trunks during
active circulation. The corpuscles change their form readily, “the
spindle-shaped ones doubling up in order to pass crossways through a
narrow aperture.... In the irregularly formed corpuscles, which seem
to represent leucocytes amœboid movements were observed....
Corpuscles pass freely above and under the tracheæ, showing that
these latter lie free in the vessels.” The hypodermis lining the
vessels is best seen in the small transverse veins.

The pulse or heart-beat of insects varies in rapidity in different insects, rising at times of excitement, as Newport noticed in _Anthophora retusa_, to 142 beats in a minute.

When an insect, as, for example, a tineid caterpillar, has been enclosed in a tight box for a day or more, the pulsations of the heart are very languid and slow, but soon, on giving it air, the pulsations will, as we have observed, rise in frequency to about 60 a minute, Herold observed 30 to 40 in a minute in a fully-grown silkworm, and from 46 to 48 in a much younger one. Suckow observed but 30 a minute in a full-grown caterpillar of _Gastropacha pini_, and 18 only in its pupa.

In a series of observations made by Newport on _Sphinx ligustri_
from the fourth day after hatching from the egg until the perfect
insect was developed, he found that before the larva cast its first
skin the mean number of pulsations, in a state of moderate activity
and quietude, was about 82 or 83 a minute; before the second moult
89, while before the third casting it had sunk down to 63; and
before its fourth to 45, while, before leaving its fourth stage, and
before it had ceased to feed, preparatory to pupating, the pulse was
not more than 39. “Thus the number gradually decreases during the
growing larva state, but the force of the circulation is very much
augmented. Now when the insect is in a state of perfect rest,
previously to changing its skin, the number is pretty nearly equal
at each period, being about 30. When the insect has passed into the
pupa state it sinks down to 22, and subsequently to 10 or 12, and
after that, during the period of hibernation, it almost entirely
ceases. But when the same insect which we had watched from its
earliest condition was developed into the perfect state in May of
the following spring, the number of pulsations, after the insect had
been for some time excited in flight around the room, amounted to
from 110 to 139; and when the same insect was in a state of repose,
to from 41 to 50. When, however, the great business of life, the
continuation of the species, has been accomplished, or when the
insect is exhausted, and perishing through want of food or other
causes, the number of pulsations gradually diminishes, until the
motions of the heart are almost imperceptible.” Insects, then, he
remarks, do not deviate from other animals in regard to their vital
phenomena, though it has been wrongly imagined that the nutrient and
circulatory functions are less active in the perfect than in the
larval condition.

The heart of a larval _Gastrus equi_ taken the day previous from a
horse’s stomach beat from 40 to 44 times a minute (Scheiber); while
Schröder van der Kolk observed only 30 beats in the same kind of
maggot.

In the larva of Corethra, while at rest, the heart contracts from 12
to 16 or 18 times a minute, but when active the number rises to 22.
The systole and diastole last from 5 to 6 minutes. (Dogiel.)

Temperature also affects the pulsations, as they increase in
frequency with a rise and decrease with a fall in temperature.

=Influence of electricity.=—The influence of electricity on the
action of the insect’s heart, from Dogiel’s experiments, is such as
to cause an acceleration in the frequency of the beats, while an
increase in the strength of the electric currents either diminishes
the frequency of the beats or entirely stops the heart’s action. A
violent excitation with the induction current causes a systole when
the heart’s action has stopped for a long time; and if the
excitation lasts uninterruptedly, then the contractions after a
while become noticeable, according to the strength of the current.
In such a case there are, however, interruptions in the regularity,
strength, and order of the contractions. (Kolbe.)

=Effects of poisons on the pulsations.=—Dogiel has also experimented
on the influence of poisons in the form of vapor or as liquid
solutions on the pulsations of insects, which is much as in
vertebrates. The application of carbonic oxide to the larva of
Corethra, whose heart one minute previous to the poisoning beat 15
times a minute, accelerated the heart-beats in about 55 minutes to
25 pulsations in a minute. Afterwards there was a retardation in the
pulse to the normal beat. Carbonic acid had a similar effect.

The following results obtained by Dogiel are somewhat as tabulated by Kolbe:—

I. Substances which cause the pulsations of the heart to accelerate.

_a._ An induction current of electricity, acting feebly.
_b._ Ammonia, acting feebly.
_c._ Ethyl ether, acting feebly.
_d._ Oxalic acid, acting feebly.
_e._ Carbolic acid, acting feebly.
_f._ Potassium nitrate, acting feebly.
_g._ Aconite, acting feebly.

II. Substances retarding the heart’s action.

_a._ An induction current of electricity, acting energetically.
_b._ Ammonia, acting energetically.
_c._ Ethyl ether, acting energetically.
_d._ Oxalic acid, acting energetically.
_e._ Carbolic acid, acting energetically.
_f._ Veratrine, acting energetically.
_g._ Atropine, acting energetically.
_h._ Aconitine, acting energetically.
_i._ Potassium nitrate, acting energetically.
_g._ Ethyl alcohol.
_h._ Chloroform.
_i._ Carbonic oxide.
_j._ Carbonic acid.
_k._ Sulphuretted hydrogen.

III. Substances whose action is indifferent.

_1._ Muscarine.
_2._ Curare.
_3._ Atropine, acting slowly.
_4._ Strychnine.

The above-named substances comprise those which in the vertebrates
effect a change in the activity of the motor nerve-ganglia of the
heart and the muscular fibres. Hence it follows that the heart of
the larval Corethra consists of muscular fibres provided with
ganglia, and that the contractions of the muscular fibres are
provoked through the agency of the ganglia. But since muscarine,
atropine, and curare, whose influence in stopping the heart’s action
of vertebrates is known, in insects either have no action or only
make the pulsations slower; it seems to follow that the heart of the
larval Corethra possesses no similar apparatus for lessening the
heart’s action, and this is also confirmed by anatomical studies. On
the contrary, aconite acts, as we must from observations conclude,
exclusively on the motor centres and the muscles, but not on the
apparatus for lessening the heart’s action, which, as has been
remarked, is not present in the larval Corethra. (Kolbe _ex_
Dogiel.)