_Libellula depressa_, showing a part of the mechanism of flight,
viz., some of the chitinous ridges at base of the upper wing, and
some of the insertions of the tendons of muscles: _A_, line of
section through the base of the upper wing, the wing being
supposed to be directed backwards. _C_, upper portion of mechanism
of the lower wing; _b_, lever extending between the pieces
connected with the two wings.—After von Lendenfeld, from Sharp.
]
As may be seen in Fig. 173, the contractile section of several of
the muscles of the wing (_s_{5}_) is extraordinarily reduced, while
its thread-like tendon is proportionately longer. This gradation
being almost like that of the pipes of an organ in the length of the
wing-muscles, as may so easily be observed in the large
dragon-flies, plainly indicates that the strain of the individual
muscles is quite different in strength, since, as the phenomenon of
flight demands it, the different parts of the base of the wing
become respectively relaxed in very dissimilar measure.
We have thus far discussed only the elevator and depressor muscles.
Other groups (_s^1s^3_) are yet to be added, however, crossing under
the first at acute angles, which when pulling the wing sidewise,
bring about in union with the other muscles a screw-like turning of
the wings.
While in dragon-flies all the muscles which are principally
influential in moving the wing are directly attached to it, and thus
evidently assert their strength most advantageously, the case is
essentially different with all other insects. Here, as has already
been superficially mentioned above, the entire set of muscles
affecting the wing is analyzed into two parts of which the smaller
only is usually directly joined to the wings, while the movement is
indirectly influenced by the remainder (Graber).
In the dragon-fly the two wings are “brought into correlative action
by means of a lever of unusual length existing amongst the chitinous
pieces in the body wall at the base of the wings (Fig. 175, _b_).
The wing-muscles are large; according to von Lendenfeld there are
three elevator, five depressor, and one abductor muscles to each
wing. He describes the wing-movements as the results of the
correlative action of numerous muscles and ligaments, and of a great
number of chitinous pieces connected in a jointed manner” (Sharp).
If again we take the longitudinal section of the thoracic cavity of
gnats in Fig. 171, we shall perceive a compactly closed system of
muscular bars intersecting each other almost at right angles and
interlaced with a tangled mass of tracheæ, some of which muscles
extend (_lm_) longitudinally, that is from the front to the back,
while others (_b-r_) stretch out in a vertical direction, that is
between the plates of the abdomen and back.
In order that we may more easily comprehend this important muscular
apparatus we will illustrate the thoracic cavity of insects by an
elastic steel ring (Fig. 172), to which we may affix artificial
wings. If this ring be pressed together from above downward, along
the line _rs_, thus imitating the pulling of the vertical or lateral
thoracic muscles, then the wings on both sides spring up. This is to
be explained by the fact that through this manipulation a pressure
is exerted on the lifting power arm of the wings. If, on the other
hand, the ring be compressed on the sides (_ml_), which is the same
thing as if the longitudinal muscles contracted the thorax from
before backward, and thus arched it more, then the wings are
lowered.
Agrioninæ, according to Kolbe, can fly with the fore pair of wings
or with the hind pair almost as well as with both pairs together.
Also the wings of these insects can be cut off before the middle of
their length without injuring their power of flight. Butterflies,
Catocalæ, and Bombycidæ fly after the removal of the hind wings.
Also the balancers of the Diptera must be useful in flying, since
their removal lessens the power of flight.
Chabrier regarded the under sides of the shell-like extended
wing-covers of the beetles as wind-catchers, which, seized by wind
currents, carry the insect through the air. We may also consider the
wing-covers as regulators of the centre of gravity of flight.
The observations of insects made by Poujade (Ann. Soc. Ent., France,
1887, p. 197) during flight teaches us, says Kolbe, that in respect
to the movement during flight of both pairs of wings, they may be
divided into two categories:—
1. Into those where both pairs of wings (together), either united,
and also when separated from each other, perform flight. Such are
the Libellulidæ, Perlidæ, Sialidæ, Hemerobiidæ, Mymeleonidæ,
Acridiidæ, Locustidæ, Blattidæ, Termitidæ, etc.
2. Into those whose fore and hind wings act together like one wing,
since they are connected by hooks (hamuli), as in certain
Hymenoptera, or are attached in other ways. Here belong Hymenoptera,
Lepidoptera, Trichoptera, Cicadidæ, Psocidæ, etc.
The musculature of the mesothorax and metathorax is similar in those
insects both of whose pairs of wings are like each other, and act
independently during flight, viz. in the Libellulidæ. On the other
hand, in the second category, where the fore and hind wings act as a
single pair and the fore wings are mostly larger than the hinder
(except in most of the Trichoptera), the musculature of the
mesothorax is more developed than that of the metathorax.
To neither category belong the beetles, whose wing-covers are
peculiar organs of flight, and not for direct use, and the Diptera,
which possess but a single pair of wings. In the beetles the hind
wings, in the Diptera the fore wings, serve especially as organs of
flight. It may be observed that the Diptera are the best fliers, and
that those insects which use both pairs of wings as a single pair
fly better than those insects whose two pairs of wings work
independently of each other. An exception are the swift-flying
Libellulidæ, whose specially formed muscles of flight explain their
unusual capabilities for flying (Kolbe).
LITERATURE ON FLIGHT
=Marey, E. J.= La machine animale. Locomotion terrestre et aërienne.
Paris, 1874.
—— Mémoire sur le vol des insectes et des oiseaux. (Annal. Scienc.
natur., 5 sér., Zool. xii, 1869, pp. 49–150; 5 sér., Zool. xv, 1872,
42 Figs.)
—— Note sur le vol des insectes. (Compt. rend. et Mém. Soc. d. Biol.
Paris, 4 sér., v, 1869, C. R. pp. 136–139.)
—— Recherches sur le mécanisme du vol des insectes. (Journal de
l’Anatomie et de la Physiologie, 6 Année, 1869, pp. 19–36, 337–348.)
—— Animal mechanism. New York, 1879, pp. 180–209.
—— Movement. New York, 1895, pp. 239–274.
=Hartings.= Ueber den Flug. (Niederland. Archiv f. Zoologie, iv,
Leiden, 1877–78.)
=Lucy.= Le vol des oiseaux, chauvesouris et insectes. Paris.
=Tatin, V.= Expériences physiologiques et synthétiques sur le
mécanisme du vol. (Ecole prat. d. haut. étud. Physiol. expérim.
Trav. du laborat. de Marey, 1877, pp. 293–302.)
—— Expériences sur le vol mécanique. (Ibid., 1876, pp. 87–108.)
=Bellesme, Jousset de.= Recherches expérimentales sur les fonctions du
balancier chez les insectes Diptères, Paris, 1878, 96 pp., Figs.
—— Sur une fonction de direction dans le vol des insectes. (Compt.
rend., lxxxix, 1879, pp. 980–983.)
=Pettigrew, J. Bell.= On the mechanical appliances by which flight is
attained in the animal kingdom. (Trans. Linn. Soc., 1868, xxvi, Pt.
I, pp. 197–277, 4 Pl.)
—— On the physiology of wings. (Trans. Roy. Soc. Edinburgh, 1871,
xxvi, pp. 321–446.)
=Krarup-hansen, C. J. L.= Beitrag zu einer Theorie des Fluges der
Vogel, Insekten und Fledermause. (Copenhagen u. Leipzig, Fritsch,
1869, 48 pp.)
=Lendenfeld, R. V.= Der Flug der Libellen. (Sitzungsber. d. kais.
Akad. d. Wiss. Wien, lxxxiii, 1881, pp. 289–376, 7 Taf.; Zool. Anz.,
1880, p. 82.)
=Girard, M.= Note sur diverses expériences relatives à la fonction des
ailes chez les insectes. (Ann. Soc. Ent. France, 4 sér., ii, 1862,
pp. 154–162.)
=Mühlhäuser, F. A.= Ueber das Fliegen der Insekten. (22. bis 24.,
Jahresb. d. Pollichia, Dürkheim, 1866, pp. 37–42.)
=Plateau, Félix.= Recherches expérimentales sur la position du centre
de gravité chez les insectes. (Archiv d. Scienc. phys. et natur. d.
Genève, Nouv. période, xliii, 1872, pp. 5–37.)
=Plateau, Félix.= Ueber die Lage des Schwerpunktes bei den Insekten.
Auszug. (Naturforscher v. Sklarek, v. Jahrg., 1872, pp. 112–113.)
—— Recherches physico-chimiques sur les articulés aquatiques. (Bull.
d. l’Acad. Roy. Belg., xxxiv, 1872, pp. 1–50, Fig.)
—— Qu’est-ce que l’aile d’un insecte? (Stett. Ent. Zeit., 1871, pp.
33–42, Pl.)
—— L’aile des insectes. (Journ. d. Zool., ii, 1873, pp. 126–137.)
=Perez, J.= Sur les causes de bourdonnement chez les insectes.
(Comptes rend., lxxxvii, p. 535, Paris, 1878.)
=Strasser, Hans.= Mechanik des Fluges. (Archiv f. Anat. u. Phys.,
1878, p. 310–350, 1 Taf.)
—— Ueber die Grundbedingungen der aktiven Locomotion. (Abhandl. d.
naturf. Gesellsch., Halle, 1880, xv, pp. 121–196, Figs.)
=Moleyre, L.= Recherches sur les organes du vol chez les insectes de
l’ordre des Hemiptères. (Compt. rend. de l’Acad. d. Scienc. de
Paris, 1882, xcv, pp. 349–352.)
=Amans, P.= Essai sur le vol des insectes. (Revue d. Sc. Nat.
Montpellier, 3 sér., ii, 1883, pp. 469–490, 2 Pl.; iii, 1884, pp.
121–139, 3 Pl.)
—— Étude de l’organe du vol chez les Hyménoptères. (Ibid., iii, pp.
485–522, 2 Pl.)
—— Comparaisons des organes du vol dans la série animale. Des organes
du vol chez les insectes. (Annal. d. Scienc. nat. Zool., 6 sér.,
xix, pp. 1–222, 8 Pl.)
=Mullenhoff, K.= Die Grosse der Flugflächen. (Pflüger’s Archiv f. d.
ges. Physiologie, 1884, xxxv, pp. 407–453.)
—— Die Ortsbewegungen der Tiere. (Wissensch. Beil. z. Programm d.
Andreas-Realgymnas. Berlin, 1885, 19 pp.)
=Poujade, G. A.= Note sur les attitudes des insectes pendant le vol.
(Ann. Soc. Ent. France, 1884, 6 sér., iv, pp. 197–200, 1 Pl.)
=Krancher, O.= Die Töne der Flügelschwingungen unserer Honigbiene.
(Deutscher Bienenfreund, 1882, 18. Jahrg., pp. 197–204.)
=Landois, H.= Ueber das Flugvermögen der Insekten. (Natur. und
Offenbarung, vi, 1860, pp. 529–540.)
=Ungern-Sternberg, von.= Betrachtungen über die Gesetze des
Fluges. (Zeitschr. d. Deutschen Vereins z. Förderung d.
Luftschiffahrt-Naturwissensch. Wochenschrift v. Potonie, iv,
1889, p. 158.)
=Baudelot, E.= Du mecanisme suivant lequel s’effectue chez les
Coléoptères le retract des ailes inférieures sous les élytres au
moment du passage a l’état de repos. (Bull. Soc. d. Scienc. nat.,
Strasbourg, 1 Année, 1868, pp. 137–138.)
=Ris, Fr.= Die schweizerischen Libellen. Schaffhausen, 1885. (Beiheft
der Mitteil. d. Schweiz. Ent. Ges., vii, pp. 35–84.)
THE ABDOMEN AND ITS APPENDAGES
[Illustration:
FIG. 176.—Abdomen of _Termes flavipes_: 1–10, the ten tergites; 1–9,
the nine urites; _c_, cercopod.
]
[Illustration:
FIG. 177.—End of abdomen of _Panorpa debilis_ drawn out, the chitinous
pieces shaded: _L_, lateral, _D_, dorsal view; _c_, jointed
cercopoda.—Gissler _del._
]
In the abdomen the segments are more equally developed than elsewhere,
retaining the simple annular shape of embryonic life, and from their
generalized nature their number can be readily distinguished (Fig. 176).
The tergal and sternal pieces of each segment are of nearly the same
size, the tergal often overlapping the sternal (though in the Coleoptera
the sternites are larger than the tergites), while there are no pleural
pieces, the lateral region being membranous when visible and bearing the
stigmata (Fig. 177, _L_). In the terminal segments beyond the genital
outlet, however, there is a reduction in and loss of segments,
especially in the adults of the metabolous orders, notably the Panorpidæ
(Fig. 177), Diptera, and aculeate Hymenoptera; in the Chrysididæ only
three or four being usually visible, the distal segments being reduced
and telescoped inward.
The typical number of abdominal segments (uromeres), _i.e._ that
occurring in each order of insects, is ten; and in certain families of
Orthoptera, eleven. In the embryos, however, of the most generalized
winged orders, Orthoptera (Fig. 199), Dermaptera, and Odonata, eleven
can be seen, while Heymons has recently detected twelve in blattid and
Forficula embryos, and he claims that in the nymphs of certain Odonata
there are twelve segments, the twelfth being represented by the anal or
lateral plates. It thus appears that even in the embryo condition of the
more generalized winged insects, the number of uromeres is slightly
variable.
We have designated the abdomen as the _urosome_; the abdominal
segments of insects and other Arthropods as _uromeres_, and the
sternal sclerites as _urosternites_, farther condensed into
_urites_. (See Third Report U. S. Entomological Commission, 1883,
pp. 307, 324, 435, etc.)
[Illustration:
FIG. 178.—Nymph of the pear tree Psylla, with its glandular
hairs.—After Slingerland. Bull. Div. Ent. U. S. Dep. Agr.
]
The reduction takes place at the end of the abdomen, and is usually
correlated with the presence or absence of the ovipositor. In the more
generalized insects, as the cockroaches, the tenth segment is, in the
female, completely aborted, the ventral plate being atrophied, while the
dorsal plate is fused during embryonic life, as Cholodkowsky has shown,
with the ninth tergite, thus forming the suranal plate.
In the advanced nymph of Psylla the hinder segments of the abdomen
appear to be fused together, the traces of segmentation being
obliterated, though the segments are free in the first stage and in
the imago (Fig. 178). It thus recalls the abdomen of spiders, of
Limulus, and the pygidium of trilobites.
=The median segment.=—There has been in the past much discussion as to
the nature of the first abdominal segment, which, in those Hymenoptera
exclusive of the phytophagous families, forms a part of the thorax, so
that the latter in reality consists of four segments, what appearing to
be the first abdominal segment being in reality the second.
Latreille and also Audouin considered it as the basal segment of the
abdomen, the former calling it the “segment médiaire,” while Newman
termed it the “propodeum.” This view was afterward held by Newport,
Schiödte, Reinhard, and by the writer, as well as Osten-Sacken,
Brauer, and others. The first author to attempt to prove this by a
study of the transformations was Newport in 1839 (article
“Insecta”). He states that while the body of the larva is in general
composed of thirteen distinct segments, counting the head as the
first, “the second, third, fourth, and, as we shall hereafter see,
in part also the fifth, together form the thorax of the future
imago” (p. 870). Although at first inclined to Audouin’s opinion, he
does not appear to fully accept it, yet farther on (p. 921) he
concludes that in the Hymenoptera the “fifth” segment (first
abdominal) is not in reality a part of the true thorax, “but is
sometimes connected more or less with that region, or with the
abdomen, being intermediate between the two. Hence we have ventured
to designate it the _thoracico-abdominal_ segment.” Had he
considered the higher Hymenoptera alone, he would undoubtedly have
adopted Latreille’s view, but he saw that in the saw-flies and
Lepidoptera the first abdominal segment is not entirely united with
the thorax, being still connected with the abdomen as well as the
thorax. Reinhard in 1865 reaffirmed Latreille’s view. In 1866 we
stated from observations on the larvæ made three years earlier, that
during the semipupa stage of Bombus the entire first abdominal
segment is “transferred from the abdomen to the thorax with which it
is intimately united in the Hymenoptera,” and we added that we
deemed this to be “the most essential zoölogical character
separating the Hymenoptera from all other insects.” (See Fig. 93,
showing the gradual transfer and fusion of this segment with the
thorax.) In the saw-flies the fusion is incomplete, as also in the
Lepidoptera, while in the Diptera and all other orders the thorax
consists of but three segments. (See also pp. 90–92.)
[Illustration:
FIG. 179.—Abdomen of _Machilis maritima_, ♀, seen from beneath: the
left half of the 8th ventral plate removed; I-IX, abdominal
segments; _c_, cercopoda; _cb_, coxal glands; _hs_, coxal stylets;
_lr_, ovipositor.—After Oudemans, from Lang.
]
=The cercopoda.=—We have applied this name to the pair of anal cerci
appended to the tenth abdominal segment, and which are generally
regarded as true abdominal legs. As is now well known, the embryos of
insects of different orders have numerous temporary pairs of abdominal
appendages which arise in the same manner, have the same embryonic
structure, and are placed in a position homologous with those of the
thorax. In the embryo of Œcanthus rudimentary legs appear, as shown by
Ayers, on the first to tenth abdominal segment, the last or tenth pair
becoming the cercopoda; and similar rudimentary appendages have been
detected in the embryos of Coleoptera, Lepidoptera, and Hymenoptera
(Apidæ). Cholodkowsky has observed eleven pairs of abdominal appendages
in Phyllodromia.
They are very long and multiarticulate in the Thysanura (Fig. 179). In
the Dermaptera they are not jointed and are forcep-like. It should also
be observed that in the larva or Sisyra (Fig. 181) there are seven pairs
of 5–jointed abdominal appendages, though these may be secondary
structures or tracheal gills. In the Perlidæ and the Plectoptera
(Ephemeridæ), they are very long, sometimes over twice as long as the
body, and composed of upward of 55 joints; they also occur in the
Panorpidæ (Fig. 177). In the dragon-flies the cerci are large, but not
articulated, and serve as claspers or are leaf-like[35] (Fig. 180). In a
few Coleoptera, as the palm-weevil (_Rhynchophorus phœnicis_), Cerambyx,
Drilus, etc., the so-called ovipositor ends in a hairy, 1–jointed,
palpiform cercus. Short 25–jointed cercopoda are present in Termitidæ,
and 2–jointed ones in Embiidæ.
[Illustration:
FIG. 180.—End of abdomen of _Æschna heros_, ♀: _ur_, urosternite;
_or_, outer, _ir_, inner styles of the ovipositor; 11, 11th
abdominal segment; _c_, cercopod.
]
[Illustration:
FIG. 181.—Larva of Sisyra, from beneath. _B_, an abdominal
appendage.—After Westwood, from Sharp.
]
[Illustration:
FIG. 182.—Cercopoda (P) of Mantis.—After Lacaze-Duthiers.
]
The anal cerci are present in the Orthoptera and, when multiarticulate,
function as abdominal antennæ. They are longest in the Mantidæ (Fig.
182); they also occur in the larva of the saw-fly, Lyda (Fig. 183). Dr.
A. Dohrn has stated that the cerci of Gryllotalpa are true sensory
organs, and we have called those of the cockroach abdominal antennæ,
having detected about ninety sacs on the upper side of each joint of the
stylets, which are supposed to be olfactory in nature, and which are
larger and more numerous than similar sacs or pits in the antennæ of the
same insect.[36] From his experiments upon decapitated cockroaches,
Graber concluded that these cerci were organs of smell.
[Illustration:
FIG. 183.—Lyda larva: _a_, head; _b_, end of body seen from above;
_c_, from side, with cercopod.
]
Haase regarded these appendages, from their late development and
frequent reduction, as old inherited appendages which are
approaching atrophy through disuse.
Cholodkowsky states that Tridactylus, a form allied to Gryllotalpa,
bears on the tenth abdominal segment two pairs of cerci (ventral and
dorsal), and that the ventral pair may correspond to the atrophied
appendages of the tenth embryonic segment of Phyllodromia, with
which afterward the eleventh segment becomes fused.
The cercopods are not necessarily confined to the eleventh or to the
tenth segment, for when there are only nine segments, with the
vestige of a tenth, as in Xiphidium, they arise from the ninth
uromere, and in the more modern cockroaches, as Panesthia, in which
there are but seven entire segments, they are appended to the last
or eighth uromere.
[Illustration:
FIG. 184.—Anabrus, ♀, side-view, dissected; showing the relative size
of the ovipositor: _c_, the minute cercopod.—Kingsley _del._
]
As to the homology and continuity of these cercopods with the ventral
outgrowths of the embryo, several embryologists, notably Wheeler, are
emphatic in regarding them as such. It thus appears that either the
embryonic appendages of the seventh or eighth, ninth or tenth uromere
may persist, and form the cercopoda of the adult.
=The ovipositor.=—The end of the oviduct is guarded by three pairs of
chitinous, unjointed styles closely fitted together, forming a strong,
powerful apparatus for boring into the ground or into leaves, stems of
plants, the bodies of insects, or even into solid wood, so that the eggs
may be deposited in a place of safety. In the ants, wasps, and bees the
ovipositor also functions as a sting, which is further provided with a
poison-sac.
Morphologically, the ovipositor is composed of three pairs of unjointed
styles (_rhabdites_ of Lacaze-Duthiers, _gonapophyses_ of Huxley), which
are closely appressed to or sheathed within each other, the eggs passing
out from the end of the oviduct, which lies, as Dewitz states, between
the two styles of the lowest or innermost pair, and under the cross-bars
or at the base of the stylets mentioned; the styles or blades spreading
apart to allow of the passage of the egg.
[Illustration:
FIG. 185.—Saw of Hylotoma: _a_, lateral scale; _i_, saw; _f_, gorget;
7_t_, 7th tergite; 6_s_, 6th sternite; _ov_, oviduct; _in_,
intestine.—After Lacaze-Duthiers.
]
The ovipositor is best developed in the Thysanura (Fig. 179, Campodea
excepted), in Orthoptera (Fig. 184), in the Odonata, Hemiptera, certain
Physapoda, Rhaphiidæ, and in the phytophagous Hymenoptera, where it is
curiously modified to form a rather complicated saw for cutting slits in
wood or leaves (Fig. 185). It is wanting or quite imperfect in
Coleoptera, Diptera, and Lepidoptera.
Morphologically, the ovipositor appears to be formed out of the
abdominal appendages of the seventh, eighth, and ninth segments of the
female, which, instead of disappearing in the orders first mentioned,
persist as permanent styles.
Wheeler asserts from his study of the embryonic development of Xiphidium
“there can be no doubt concerning the direct continuity of the embryonic
appendages with the gonapophyses.” He goes on to say:—
“One embryo, which had just completed katatrepis, still showed
traces of all the abdominal appendages. The pairs on the eighth,
ninth, and tenth segments were somewhat enlarged. In immediately
succeeding stages the appendages of the second to sixth segments
disappear; the pair on the seventh disappear somewhat later. Up to
the time of hatching the gonapophyses could be continuously traced,
since in Xiphidium there is no flexure of the abdomen, as in other
forms, to obscure the ventral view of the terminal segments. From
the time of hatching Dewitz has traced the development of the
ovipositor in another locustid (_Locusta viridissima_), so that now
we have the complete history of the organ.”
Heymons, however, is inclined to believe that they are simply hypodermal
outgrowths.
[Illustration:
FIG. 186.—Ideal plan of the structure of the ovipositor to illustrate
Lacaze-Duthiers’ view: _b_, 8th tergite; _c_, epimerum; _a′_, _a_,
two pieces forming the outer pair of rhabdites; _i_, the 2d pair, or
stylets; and _f_, the inner pair, or sting; _d_, support of sting;
_e_, piece supporting the stylet; _R_, anus; _o_, outlet of oviduct.
The 7th, 8th, and 9th sternites are aborted.—After Lacaze-Duthiers.
]
The first to study the morphology of the ovipositor was Lacaze-Duthiers,
who referred their origin to the partially atrophied dorsal or ventral
sclerites of one of the last abdominal segments; a view accepted by
Gerstaecker[37] (Figs. 186, 187). The present writer (1866), however,
showed that the sting of Bombus was not formed of the reduced pieces of
the segments themselves, but arose from special outgrowths on the
ventral side of the eighth and ninth abdominal segments. These
appendages he did not at first regard as the homologues of the limbs,
until in 1871, after studying the origin of the spring of the Podurans
(Isotoma), he found that it was a true jointed appendage and therefore a
homologue of a pair of the styles forming the ovipositor of the winged
insects, and that the three pairs of styles of the latter were
homologues of the thoracic legs and cephalic appendages. The view was
stated in the Guide to the Study of Insects. (See also Amer. Nat.,
March, 1871, p. 6.) Kraepelin also affirms that the styles of the
ovipositor are segmental appendages and homologues of the antennæ, wings
(_sic_), and legs.
[Illustration:
FIG. 187.—1, abdomen of Cynips, showing the great dorsal segment, the
peduncle, and the position of the ovipositor within; 2, the entire
ovipositor; _a_, lateral scale; _a′_, its valve; _b_, anal scale;
_b′_, stylet; _c_, support of the stylet; _e_, base or support of
sting (_fi_); 3, profile showing the relation of the genital
armature to the rest of the abdomen, the 6th sternite having been
drawn to show its full size; 4, anal scale (_b_) and stylet; _e_,
_i_, supports and body of the stylet; _c_, piece uniting the two
scales; 5, lateral scale (_a_), and _a_′ sheath; _d_, support of the
sting (_f_); 6, transverse section of the body through the sting
(diagrammatic); _R_, internal armature; _o_, oviduct; _a_, lateral
scale; _a′_ its valve; _e_, support of the stylets (_i_); _b_, anal
scale; _c_, piece uniting two scales; _f_, sting; _d_, its support;
7, a second section simpler and more theoretical than the first; 8,
diagrammatic, all the elements of the sting have been reduced to
pieces of the same form.—After Lacaze-Duthiers.
]
An objection to this view is the fact that the posterior pairs of styles
appear to arise both from one and the same segment,—the ninth. Dewitz
questions whether the four appendages of the ninth segment represent two
pairs of limbs, or one pair split into two branches, and prefers the
latter view, but leaves it as a point to be settled by future
investigations. As will be seen below, both Kraepelin and Bugnion
observed a pair of rudiments to each of the three penultimate segments,
those of the middle pair splitting in two. Wheeler maintains,
erroneously we think, that the inner of the two pairs on the ninth
segment represents the tenth pair of abdominal appendages; but in
reality this latter pair become the cercopods. That there are probably
originally in insects of all the orders provided with an ovipositor
three distinct pairs of appendages, one to each segment, is proved, or
at least strongly suggested, by Ganin’s researches on the three pairs of
abdominal imaginal discs of the third larva of Platygaster and Polynema
(Fig. 188), which are transformed into the ovipositor. He remarks that
these imaginal discs have the same origin and pass through the same
changes as those in front, _i.e._ those destined to form the thoracic
legs. Dewitz has shown that the germs of the ovipositor of the honey-bee
arise as buds on the two segments before the last (Fig. 189).
[Illustration:
FIG. 188.—Third larva of Polynema: _at_, antenna; _fl_, imaginal buds
of the wing; _l_, of the legs; _tg_, buds of the middle pair of
stylets of the ovipositor; _fk_, fat-body; _eg_, ear-like
process.—After Ganin.
]
[Illustration:
FIG. 189.—Imaginal buds and papillæ of the ovipositor of the honey-bee
attached to tracheæ; at different stages: _b′_, 1st; _b″_, 2d or
middle; and _c′_, 3d pair of papillæ.—After Dewitz.
]
Kraepelin also detected in the larva of the honey-bee a pair of what he
regarded as genuine imaginal buds on abdominal segments eight, nine, and
ten; the buds on the tenth segment are divided each in two; of these
four appendages the two median ones form the barbed sting (_gorgeret_ or
_stachelrinne_), and the two lateral stylets, the valves
(_stachelscheiden_). The two buds of the ninth segment give rise to the
vagina and to the oviducts, and these unite secondarily with the
posterior end of the ovaries. The genital appendages of the male
correspond to those of the female, and arise from four imaginal buds
situated on the under side of the tenth abdominal segment.
[Illustration:
FIG. 190.—1, sting and poison sac of the honey-bee: _GD_, poison
gland; _Gb_, poison reservoir; _D_, accessory gland; _sh_, sheathing
style or sting-“feeler”; _Str_ sting; _Ba_, sheath; _Q_, quadrate
plate; _O_, oblong piece; _W_, angular piece; _B_, base of the sting
and stylets; _Stb′_, _Stb″_, the two barbed stylets or darts. 2,
sting seen from the ventral face: lettering as in the other
figure.—After Kraepelin, from Perrier.
]
In the ants, according to Dewitz, the genital armature is derived from
imaginal buds situated on the under side of the seventh, eighth, and
ninth abdominal segments. Bugnion has observed the formation of six
imaginal buds of the genital armature in the larva of a chalcid
(Encyrtus, Figs. 41, 42, 191, _q^1_, _q^2_, _q^3_), the transformation
of the central part of these structures into small digitiform pads, then
the division of the two intermediate buds into four (?) (Fig. 191, _B_,
_q^2_), but was unable to trace their farther development.
The subject still needs farther investigation, since certain
observers, as Haase, and, more recently, Heymons, do not believe
that they are homologues of the legs, but integumental structures,
though of somewhat higher value than the style of the base of the
legs of Scolopendrella and Thysanura; but it is to be observed that
as yet we know but little of the embryological history of these
styles.
Those authors who have examined the elements of the ovipositor, and
regard them as homologues (_homodynamous_) of the limbs, are
Weismann (1866), Ganin (1869), Packard (1871), Ouljanin (1872),
Kraepelin, Kowalevsky (1873), Dewitz (1875), Huxley (1877),
Cholodkowsky, Bugnion (1891), and Wheeler (1892).
As shown, then, by our observations and those of Dewitz (Figs. 189 and
192), the rudiments of the ovipositor consist of three pairs of
tubercles, arising, as Kraepelin and also Bugnion (Fig. 191) have shown,
from three pairs of imaginal discs, situated respectively on the
seventh, eighth, and ninth uromeres, or at least on the three
penultimate segments of the abdomen. With the growth of the semipupa,
the end of the abdomen decreases in size, and is gradually incurved
toward the base (Fig. 193), and the three pairs of appendages approach
each other so closely that the two outer ones completely ensheath the
inner pair, until a complete extensible tube is formed, which, by the
changes in form of the muscles within, is gradually withdrawn entirely
within the body.
[Illustration:
FIG. 191.—_A_, end of larva of Encyrtus of 2d stage, showing the three
pairs of imaginal buds of the ovipositor _q^1_, _q^2_, _q^3_. _B_,
the same in an older larva ready to transform; _i_, intestine; _x_,
genital gland; _a_, anus.—After Bugnion.
]
An excellent account of the honey-bee’s sting is given by Cheshire
(Figs. 194, 195). The outermost of the three pairs of stylets
forming the apparatus is the two thick, hairy “palpi” or feelers
(_P_), these being freer from the sting proper than in the
ovipositor of Orthoptera. The sting itself is composed of the two
inner pairs of stylets; one of these pairs is united to form the
sheath (_sh_), while the other pair form the two barbed darts. The
sheath has three uses: first, to open the wound; second, to act as
an intermediate conduit for the poison; and third, to hold in
accurate position the long barbed darts. The sheath does not enclose
the darts as a scabbard, but is cleft down the side presented in
Fig. 194, which is below when the sting points backward. But, says
Cheshire, as the darts move up and down, they would immediately slip
from their position, unless prevented by a mechanical device,
exhibited by _B_ and _C_, giving in cross-section sheath and darts
near the end, and at the middle of the former. “The darts (_d_) are
each grooved through their entire length, while upon the sheath
(_sh_) are fixed two guide rails, each like a prolonged dovetail,
which, fitted into the groove, permits of no other movement than
that directly up and down.” The darts are terminated by ten barbs of
ugly form (_D_, Fig. 194), and much larger than those of the sheath,
and as soon as the latter has established a hold, first one dart and
then the other is driven forward by successive blows. These in turn
are followed by the sheath, when the darts again more deeply plunge,
until the murderous little tool is buried to the hilt. But these
movements are the result of a muscular apparatus yet to be examined,
and which has been dissected away to bring the rigid pieces into
view. The dovetail guides of the sheath are continued far above its
bulbous portion, as we see by _E_, Fig. 195; and along with these
the darts are also prolonged upward, still held to the guides by the
grooved arrangement before explained; but both guides and darts, in
the upper part of their length, curve from each other somewhat like
the arms of a Y, to the points _c_, _c′_ (_A_, Fig. 194), where the
darts make attachment to two levers (_i_, _i′_). The levers (_k_,
_l_ and _k′_, _l′_) are provided with broad muscles, which terminate
by attachment to the lower segments of the abdomen. These, by
contraction, revolve the levers aforesaid round the points _f_,
_f′_, so that, without relative movement of rod and groove, the
points _c_, _c′_ approach each other. The arms of the Y straighten
and shorten, so that the sheath and darts are driven from their
hiding-place together and the thrust is made by which the sheath
produces its incision and fixture. The sides being symmetrical, we
may, for simplicity’s sake, concentrate our attention on one, say
the left in the figure. A muscular contraction of a broad strap
joining _k_ and _d_ (the dart protractor) now revolves _k_ on _l_,
so that _a_ is raised, by which clearly _c_ is made to approach _d_;
_i.e._ the dart is sent forward, so that the barbs extend beyond the
sheath and deepen the puncture. The other dart, and then the sheath,
follow, in a sequence already explained, and which _G_, Fig. 195, is
intended to make intelligible, _a_ representing the entrance of the
sheath, _b_ the advance of the barbs, and _c_ the sheath in its
second position. The barb retractor muscle is attached to the outer
side of _i_, and by it _a_ is depressed and the barbs lifted. These
movements, following one another with remarkable rapidity, are
entirely reflex, and may be continued long after the sting has been
torn, as is usual, from the insect. By taking a piece of
wash-leather, placing it over the end of the finger, and applying it
to a bee held by the wings, we may get the fullest opportunity of
observing the sting movements, which the microscope will show to be
kept up by continued impulses from the fifth abdominal ganglion and
its multitudinous nerves (_n_, Fig. 194, _A_), which penetrate every
part of the sting mechanism, and may be traced even into the darts.
These facts, together with the explanation at page 49, will show why
an abdomen separated many hours may be able to sting severely, as I
have more than once experienced.
[Illustration:
FIG. 192.—Base of the ovipositor of _Locusta viridissima_ seen from
beneath: _c′_, sheath, or outer and lower pair of stylets turned to
one side to show the others; _b′_, upper and inner pair; _b″_, third
or innermost, smallest pair of stylets. _A_, the same on one side,
in section. The shaded parts show the muscular attachments. The
muscles which extend the apparatus and are attached to ν, δ, and η,
as also the membranes which unite the pieces from η; to γ with each
other and the body, are removed, so that only the chitinous parts
remain.—After Dewitz.
]
[Illustration:
FIG. 193.—Development of the sting in Bombus: _A_, _a_, 1st pair on
8th sternite; _b_, 2d inner pair forming the darts; _c_, outer pair.
_B_-_E_, more advanced stages. _F_, _x_, _y_, _z_, three pairs of
tubercles, the germs of the male organs.
]
[Illustration:
FIG. 194.—Sting of bee × 30 times: _A_, sting separated from its
muscles; _ps_, poison sac; _pg_, poison gland; _5th g_, 5th
abdominal ganglion; _n_, _n_, nerves; _e_, external thin membrane
joining sting to last abdominal segment; _i_, _k_, _l_, and _i′_,
_k′_, _l′_, levers to move the darts; _sh_, sheath; _v_, vulva; _p_,
sting-palpus or feeler, with tactile hairs and nerves. _B_ and _C_,
sections through the darts and sheath, × 300 times: _sh_, sheath;
_d_, darts; _b_, barbs; _p_, poison-channel. _D_, end of a dart, ×
200: _o_, _o_, openings for poison to escape into the wound.—After
Cheshire.
]
[Illustration:
FIG. 195.—Details of sting of bee: _E_, darts, sheath, and valves;
_pb_, poison-bag duct; _fo_, fork; _s_, slide piece; _va_, valve;
_b_, barbs. _F_, terminal abdominal segments; _w_, worker’s sting;
_q_, queen’s sting; _r_, _r′_, anal plate; _G_, sting entering skin;
_sh_, sheath; _a_, _b_, _c_, positions in first, second, and third
thrusts with the sting. _H_, portion of poison gland, × 300; _cn_,
cell nucleus; _n_, nerve; _g_, ganglionic cell. _I_, portion of the
poison gland, cells removed; _cd_, central duct; _d_, individual
small ducts; _pr_, tunica propria. _K_, gland of _Formica rufa_;
_cd_, central duct; _d_, small ducts; _sc_, secreting cells. _L_,
valve and support; _t_, trachea; _va_, valve; _tr_, truss or
valve-prop.—After Cheshire.
]
[Illustration:
FIG. 196.—_A_, rudimentary ovipositor of nymph of Æschna. _B_, the
corresponding ♂ structures; _a_, enlarged. _C_, ovipositor of nymph
of Agrion; _d_, gill.
]
The male genital armature in the bees is originally composed of three
pairs of tubercles, homologous with those of the female, all originally
arising from three abdominal segments, two afterward being anterior, and
the third pair nearer the base of the abdomen.
The ovipositor of the dragon-flies (Odonata) is essentially like that of
the Orthoptera and Hymenoptera. Thus in Æschna (Fig. 196), Agrion (Fig.
196, _C_), and also in Cicada it consists of a pair of closely appressed
ensiform processes which grow out from under the posterior edge of the
eighth uromere and are embraced between two pairs of thin lamelliform
pieces of similar form and structure.
=The styles and genital claspers= (_Rhabdopoda_).—Other appendages of
the end of the abdomen of pterygote insects, and generally, if not
always, arising from the ninth segment, are the clasping organs, or
_rhabdopoda_ as we may call them, of Ephemeridæ (Fig. 197), Neuroptera
(Corydalus [Fig. 198], Myrmeleon, Rhaphidia), Trichoptera, Lepidoptera,
Diptera, and certain phytophagous Hymenoptera. They do not appear to
occur in insects which are provided with an ovipositor. In Thysanura the
styles are present on segments 1–9 (Fig. 179). Those of the male
Ephemeridæ, of which there are two pairs arising from the ninth segment,
are remarkable, since they are jointed, and they serve to represent or
may be the homologues of two of the pairs of stylets composing the
ovipositor of insects of other orders. The lower pair (Fig. 197, _rh_)
are either 2–, 3–, or 4–jointed (in Oniscigaster 5–jointed), while those
of the upper pair are 2–jointed (_rh′_). These rhabdopods in the
ephemerids are evidently very primitive structures, since they approach
nearest in shape and in being jointed to the abdominal legs of
Scolopendrella and the Myriopoda. The styles of the Orthoptera are
survivals of the embryonic appendages of the ninth segment (Wheeler,
etc.). In Mantis they are seen to have the same relations as the cerci,
as shown by Heymons (Fig. 200).
[Illustration:
FIG. 197.—Abdomen of _Ephemera_ (Leptophlebia) _cupida_, ♂: _c_, base
of cercopoda; _rh_, outer 3–jointed claspers or rhabdopods; _rh′_,
inner pair. _A_, side view.
]
[Illustration:
FIG. 198.—End of abdomen of _Corydalus cornutus_, ♂: _vh_, rhabdopod;
_c_, cercopod.
]
In the Phasmidæ, in Anabrus, and in the Odonata the cercopods, which are
not jointed, are converted into claspers, and in the Odonata the
claspers are spiny within, so as to give a firmer hold. The suranal
plate is apparently so modified as to aid in grasping the female. In
nearly all the Trichoptera there are, besides the suranal plate, which
is sometimes forked (Nosopus), a pair of superior and of inferior
claspers, and in certain genera (Ascalaphomerus, Macronema, Rhyacophila,
Hydropsyche, Amphipsyche, Smicridea, and Ganonema) the lower pair are
2–jointed like those of Ephemeridæ. The number of abdominal segments in
the adult Trichoptera is nine, and McLachlan states that the genital
armature consists of three pairs of appendages, _i.e._ a superior,
inferior, and intermediate pair, besides the suranal plate (vestige of a
tenth segment) and the penis. Judging by his figures, these three pairs
of appendages arise from the last or ninth uromere, and the upper pair
seem to be the homologue of the cercopoda of ephemerids. It needs still
to be ascertained whether the intermediate pair is a separate set, or
merely subdivisions of the upper or lower, and whether one of the latter
may not arise from the penultimate segment, because we should not expect
that the last segment should bear more than one pair of appendages, as
we find to be the case in arthropods in general, and in the Neuroptera,
from which the Trichoptera may have originated.
[Illustration:
FIG. 199.—End of abdomen of embryo of Mantis: _r_, rhabdopod; _c_,
cercopod; _sp_, suranal plate; _st_, stigma on 8th segment.—After
Heymons.
]
[Illustration:
FIG. 200.—End of abdomen of _Periplaneta americana_, ♂, side view:
_c_, cercopod; _st_, stilus; _p_, penis; _t_, titillator; _d_,
“bird’s head” (clasper?); _i_, “oblong plate”; IX-XI, terminal
segments; X, suranal plate; XI′, 11th sternite.—After Peytoureau.
]
In most larvæ of the Trichoptera, especially the Rhyacophilidæ and
Hydropsychidæ, the last abdominal segment bears a pair of 2–jointed legs
(cercopoda), ending in either one or two claws, which under various
forms, sometimes forming long processes, persist in the pupa; and there
appears to be a suranal plate, the vestige of the tenth uromere. In the
pupa, judging by Klapálek’s figure of Leptocerus (24_{8,9}, 25), a pair
of lateral spines arise which may in the imago form one of the pairs of
appendages or styles. In the pupa of _Œcetis furva_ his figure 28_{9}
shows two pairs of 1–jointed appendages arising from the last segment;
whether the long dorsal or upper styles arise from the vestige of a more
distal segment is not distinctly shown in Klapálek’s sketch. The origin
of these elements of the genital armature evidently needs further study.
Whether the abdominal legs or so-called false or prop-legs of
lepidopterous larvæ are genuine legs, homologous with those of the
thorax and with the cephalic appendages, or whether they are secondary
adaptive structures, is a matter still under discussion. That, however,
they are true legs is shown by the embryology of the Lepidoptera, where
there is a pair to each abdominal segment. It may also be asked whether
the anal legs of lepidopterous larvæ are not the homologues of the
2–jointed anal appendages of caddis-worms.
[Illustration:
FIG. 201.—_Eriocephala calthella_, ♂, side view: _t_, palpiform
suranal plate; _cl_, claspers; _s_, inferior claspers; _mxp_,
maxillary palpi; _cx_. coxa; _tr_, trochanter; _sc_, scutum; _sc′_,
scutellum.
]
In Lepidoptera, notably the male of the very generalized _Eriocephala
calthella_ (Fig. 201), besides the broad unjointed claspers, which are
curved upward and provided with a brush of stiff hooked setæ (this upper
pair being perhaps modified cercopods), there is an accessory lower
slenderer pair, while the suranal plate (_t_) is palpiform or clavate
and also adapted to aid in the action of the claspers. The examination
of the cercopods and rhabdopods in the Trichoptera and in a generalized
lepidopterous form like this enables one to understand the morphology of
the genital armature, since it consists, besides the suranal plate,
which is often deeply forked (in Sphingidæ, Smith), of a pair of
modified hook-like cercopoda, and in some cases (Eriocephala) of an
additional pair of claspers which may be the homologues of the ephemerid
rhabdopods. A pair of hooks, often strong and claw-like (_harpes_), are
situated, one near the base on the inside of each clasper; they are
especially developed in the Noctuidæ (Smith), and appear to be present
in certain Trichoptera, but this remains to be proved. This complicated
apparatus of claspers and hooks is utilized by those insects which pair
while on the wing, and is wanting in such forms as Coleoptera and
Hemiptera. Besides the forceps of Panorpa, there are two pairs of
slender filiform appendages which need farther examination. In the
Diptera, especially Tipulidæ, there is a pair of 2–jointed appendages or
forceps, as in Limnophila (Osten Sacken). The male genital armature of
Diptera appears to be on the same general plan as in Lepidoptera, but
more complicated.
[Illustration:
FIG. 202.—Male organs of generation of Athalia.—After Newport.
]
Notice should also be taken of the paired uncinate hooks which are
modifications of the penis-sheath of the male of cockroaches
(Phyllodromia), which Haase states appear to originate on the tenth
ventral plate, and which probably “serve to open and dilate the vagina
of the female, especially as a perforated penis, which is highly
developed in Machilis, seems to be wanting in the Blattidæ.” (Haase.)
=The penis.=—This is a single or double median style-like structure
either hollow and perforated, or solid, very variable in shape,
receiving the end of the ejaculatory duct. It is usually enclosed
between two lateral plates, the homologues perhaps of the inner pair of
sheaths of the ovipositor. In the Coleoptera, as in Carabidæ and
Melolonthidæ, the penis is a long chitinous tube, “retractile within the
abdomen on the under surface as far as the anterior segments.”
(Newport.) In the Hymenoptera, of which that of the saw-flies is a type,
Newport states that it “consists of a short valvular projectile organ,
covered externally by two pointed horny plates (_i_) clothed with soft
hairs.” Above these are two other irregular double-jointed plates (Fig.
202, _l_) surrounded at their base by a chitinous ring (_k_); they are
edged with prehensile hooked spines (_i_). Between these in the middle
line are two elongated muscular parts (_m_) which enclose the penis
(_h_), and which, like those in beetles, perhaps aid in dilating the
vulva of the female.
An examination of Figs. 203–207 will aid in understanding the various
modifications in beetles, etc., of this organ.
A general study of the anatomy and homologies of the male genital
armature, from a developmental point of view, together with a comparison
of them with the corresponding female organs, is still needed.
[Illustration:
FIG. 203.—End of abdomen situated under the anal lobes of _Hydrophilus
piceus_, drawn out, seen from the ventral side: 6, sternal region of
6th segment; 7, 8, 9, segments telescoped, when retracted, in 6th
segment; _zw_, membrane connecting 6th and 7th segments; _G_,
intromittent apparatus; _vl_, external lobes; _vlu_, inner lobes;
_pn_, penis.
]
[Illustration:
FIG. 204.—The same as in Fig. 203, seen from the side: 6, the free 6th
segment; 7–10, the four last, when at rest, retracted and telescoped
within the 6th segment, with the copulatory apparatus (_g_); _vl_,
outer, _vlu_, inner lobe; 10_s_, tergite of 10th segment; 10_i_,
sternite of the same; _an_, anal opening.
]
[Illustration:
FIG. 205.—Terminal parts of the male copulatory apparatus of
_Hydrophilus piceus_, torn apart: _vlu_, the two inner lodes; _pn_,
penis; _x_, membrane torn from under side of penis; _ej_,
ejaculatory duct; _os_, its opening on the under side of the penis,
directly under its tip. The muscles, tracheæ, and nerves are not
drawn.
]
=Velum penis.=—In the locusts (Acrydiidæ) the penis is concealed by a
convex plate, flap, or hood, free anteriorly and attached posteriorly
and on the sides to the ridge forming the upper edge of the tenth
sternite. When about to unite sexually, the tip of the abdomen is
depressed, the hood is drawn backward, uncovering the chitinous penis.
=The suranal plate.=—This is a triangular, often thick, solid plate or
area, the remnant of the tergum of the last, usually tenth, segment of
the abdomen, the supra-anal or suranal plate, or anal operculum (_lamina
supra-analis_) of Haase. In most lepidopterous larvæ this plate is well
marked; in those of the Platypteridæ it is remarkably elongated, forming
an approach to a flagellum-like terrifying appendage, and in that of
_Aglia tau_ it forms a long, prominent, sharp spine. In the cockroach,
both Cholodkowsky and Haase maintain that the tenth abdominal segment is
suppressed in the female, the tergal portion being fused with the
suranal plate (the latter in this case, as we understand it, being the
remnant of the eleventh segment of the embryo). As to the nature of the
middle jointed caudal appendage in Thysanura and May-flies Heymons has
satisfactorily shown that it is a hypertrophied portion of the suranal
plate, being in Lepisma but a filamental elongation of the small
eleventh abdominal tergite.
[Illustration:
FIG. 206.—Copulatory organ of a weevil, _Rhychophorus phœnicis_, seen
from above. _A_, _vl_, the lobes united into a capsule; _pp_, torn
membrane which connects the capsule with the 9th abdominal segment;
_ej_, ejaculatory duct. _B_, the same seen from the side; _mu_, end
of the muscle of the penis. _C_, the same as _B_, without the
capsule; _os_, opening of the ejaculatory duct (_ej_). Other letters
as in _A_.
]
[Illustration:
FIG. 207.—_A_, penis (_pn_) of _Carabus hortensis_: _bl_, wrinkled
membranous vesicle; _vlu_, the valves; _g_, part of 9th segment.
_B_, end of penis of the same, enlarged; _os_, cleft-like opening;
also a wrinkled vesicle, as at _bl_.—This and Figs. 203–205 after
Kolbe.
]
At the base of the suranal plate of locusts (Acrydiidæ) is the suranal
fork or suranal furcula (_furcula supra-analis_, as we have called it)
(Fig. 88, 89, _f_).
=The podical plates or paranal lobes.=—In the cockroach and other
insects, also in the nymphs of Odonata, the anus is bounded on each side
by a more or less triangular plate, the two valves being noticeable in
lepidopterous larvæ. They are the _valvulæ_ of Burmeister, and podical
plates of Huxley, who also regarded them as the tergites of an eleventh
abdominal segment;[38] and the subanal laminæ of Heymons. They are
wanting in Ephemeridæ.
=The infra-anal lobe.=—Our attention was first called to this lobe or
flap, while examining some geometrid larvæ. It is a thick, conical,
fleshy lobe, often ending in a hard, chitinous point, and situated
directly beneath the vent. Its use is evidently to aid in tossing the
pellets of excrement away so as to prevent their contact with the body.
The end may be sharp and hard or bear a bristle. Whether this lobe is
the modified ventral plate of the ninth urite, we will not undertake at
present to say.
=The egg-guide.=—In the Acrydiidæ the external opening of the oviduct is
bounded on the ventral side by a movable, triangular, acute flap, the
egg-guide (Fig. 88, _B_, _eg_). Whether this occurs in other orders
needs to be ascertained.
LITERATURE ON THE ABDOMEN AND ITS APPENDAGES
_a._ General (including the cerci, stili, etc.)
=Cornelius, C.= Beiträge zur naheren Kenntnis von _Palingenia
longicauda_. (Programm d. Real- u. Gewerbeschule zu Elberfeld, 1848,
pp. 1–38, 4 Taf.)
=Schiödte, J. G.= Bemerkungen über Myrmecophilen. Ueber den Bau des
hinterleibes bei einigen Käfergattungen. (Germar’s Zeits. f. Ent.,
1844.)
—— De metamorphosi Eleutheratorum observationes. (Naturhist. Tidsskr.
i-xiii, 1861–1883.)
=Meinert, F.= Anatomia Forficularum. Anatomisk undersogelse af de
Danske Orentviste, i. (Naturhist. Tidsskr. 3 raekke, ii, 1863, pp.
427–482, 1 Pl.)
—— Om dobbelte Saedgange hos insecter. (Naturhist. Tidsskrift, 3
raekke, v, 1868.)
=Tullberg, Tycho.= Sveriges Podurider. (Svenska Vetensk.-Akad. Handl.,
1872, x, Nr. 10, 12 Pls.)
=Davis, H.= Notes on the pygidia and cerci of insects. (Journ. R.
Micr. Soc., 1879, ii.)
=Westhoff, F.= Ueber den Bau des Hypopygiums der Gattung Tipula Meig.
(Münster, 1882, pp. 1–62, 6 Taf.)
=Saunders, Edward.= Further notes on the terminal segments of aculeate
Hymenoptera. (Trans. Entom. Soc. London, 1884, pp. 251–267, 1 Pl.)
=Palmén, J. A.= Ueber paarige Ausführungsgange der Geschlechtsorgane
bei Insekten. (Helsingfors, 1884, 5 Taf.)
=Haase, E.= Die Abdominalanhänge der Insekten mit Berücksichtigung der
Myriopoden. (Morpholog. Jahrbuch, 1889, xv, pp. 331–435, 2 Taf.)
—— Abdominalanhänge bei Hexapoden. (Sitzungsber. d. Gesellsch.
naturforsch. Freunde, 1889, pp. 19–29.)
=Wheeler, William M.= On the appendages of the first abdominal segment
of embryo insects. (Trans. Wis. Acad. Sc., viii, 1890, pp. 87–140, 3
Pls.)
=Janet, Charles.= Études sur les fourmis, 5^e note, sur la morphologie
du squelette des segments post-thoraciques chez les Myrmicides.
(Mém. Soc. Acad, de l’Oise, xv, pp. 591–611, Figs. 1–5, 1894.)
=Heymons, Richard.= Die Segmentirung des Insektenkörpers. (Anh. Abh.
Akad. Berlin, Phys. Abh., pp. 39, Taf., 1895. See also Die
Embryonalent, von Dermapteren und Orthopteren, under Embryology.)
—— Grundzüge der Entwicklung und des Körperbaues von Odonaten und
Ephemeriden. (Abhandl. k. Preuss. Akad. d. Wissens. Berlin, 1896, 2
Taf., pp. 1–66.)
—— Zur Morphologie der Abdominalanhänge bei den Insecten. (Morphol.
Jahrb., iv, 1896, pp. 178–203, 2 Taf.)
=Peytoureau, S. A.= Contribution à l’étude de la morphologie de
l’armure génital des insectes. (Bordeaux, 1895, pp. 248, 22 Pls., 43
Figs. in text.)
=Verhoeff, C.= Cerci und styli der Tracheaten. (Ent. Nachr., xxi, pp.
166–168, 1895.)
Also the writings of Oudemans, Packard, etc.
_b._ The ovipositor
=Lacaze-Duthiers, Henri.= Recherches sur l’armure génitale femelle des
insectes. (Ann. d. sc. natur., 1849, xii, pp. 353–374, 1 Pl.; 1850,
xiv, pp. 17–52, 1 Pl. (Hyménoptères); 1852, xvii, pp. 206–251, 1 Pl.
(Orthoptères); 1853, xix, pp. 25–88, 4 Pl. (Neuroptères, Thysanures,
Coléoptères, Diptères); pp. 203–237 (Lépidoptères, Aphaniptères en
general. Also separate.))
=Sollmann, A.= Der Bienenstachel. (Zeitschr. f. Wissens. Zool., xiii,
1863, pp. 528–540, 1 Taf.)
=Fengger, H.= Anatomie und Physiologie des Giftapparates bei den
Hymenopteren. (Archiv f. Naturgesch., 1863, pp. 139–178, 1 Taf.)
=Eaton, A. E.= Remarks upon the homologies of the ovipositor. (Trans.
Ent. Soc. London, 1868, pp. 141–144.)
=Packard, A. S.= On the structure of the ovipositor and homologous
parts in the male insects. (Proc. Boston Soc. Nat. Hist., xi, 1868,
pp. 393–399, Figs. 1–11.)
=Lambrecht, A.= Samtliche Teile des Stechapparates in Bienenkörper und
ihre Verwendung zu technischen und vitalen Zwecken. (Bienemwirtsch.
Centralbl., 7 Jahrg., 1871, pp. 5–11.)
=Kraepelin, K.= Untersuchungen über den Bau, Mechanismus und die
Entwicklung des Stachels der bienenartigen Tiere. (Zeitschr. f.
wiss. Zoologie, xxiii, 1873.)
=Dewitz, H.= Vergleichende Untersuchungen über Bau und Entwicklung des
Stachels der Honigbiene und der Legescheide der grünen Heuschrecke.
(Königsberg, 1874.)
—— Ueber Bau und Entwicklung des Stachels und der Legescheide einiger
Hymenopteren und der grünen Heuschrecke. (Zeitschr. f. wissen.
Zoologie, xxv, 1874, pp. 174–200, 2 Taf.)
—— Ueber Bau und Entwicklung des Stachels der Ameisen. (Zeitschr. f.
wiss. Zoologie, 1877, xxviii, pp. 527–556, 1 Taf.)
=Adler, H.= Legeapparat und Eierlegen der Gallwespen. (Deutsche Entom.
Zeitschr., 1877, xxi Jahrg., pp. 305–332, 1 Taf.)
=Cholodkowsky, N.= Ueber den Hummelstachel und seine Bedeutung für die
Systematik. (Zool. Anzeiger, vii, 1884, pp. 312–316.)
=Ihering, H. von.= Der Stachel der Meliponen. (Ent. Nachr., 1886, xii,
Jahrg., pp. 177–188, 1 Taf.)
=Meinert, F.= Bidrag til de danske Myrers Naturhistorie. (Kjöbenhavn,
1890, 68 s.u. Danske Vidensk. Selsk. Skrifter, 5 Raek, v, 3 Pls.)
=Beyer, O. W.= Der Giftapparat von _Formica rufa_ ein reduziertes
Organ. (Jena. Zeitschr. Naturw., 1890, xxv, pp. 26–112, 2 Taf.)
=Carlet, G.= Mémoire sur le venin et l’aiguillon de l’abeille. (Ann.
d. sc. nat. Zool., 7 sér., ix, 1890, pp. 1–17, 1 Pl.)
=Künckel d’Herculais, J.= Méchanisme physiologique de la ponte chez
les insectes orthoptères de la famille des Acridides.—Rôle de l’air
comme agent mécanique et fonctions multiples de l’armure génitale.
(Compt. Rend., cxix, pp. 244–247, 1894.)
Also the writings of Verhoeff, Heymons.
_c._ The external genital armature
=Klug, Johann C. F.= Versuch einer Berichtigung der Fabriciusschen
Gattungen Scolia u. Tiphia. (Ueber u. Mohr Beiträge zur Naturkunde,
i, pp. 8–40, 1805, 1 Taf.)
=Audouin, J. V.=, and =Lachat=. Observations sur les organes
copulateurs males des Bourdons. (Annal. général, d. sc. phys., 1821,
viii, pp. 285–289.)
=Audouin, J. V.= Lettre sur la génération des insectes. (Ann. des sc.
nat., sér. 1, ii, 1824.)
=Suckow, F. W.= L. Geschlechtsorgane der Insekten. (Heusinger,
Zeitschr. organ. Physik., 1828, ii, pp. 231–264, 1 Taf.)
=Rathke, H.= De Libellularum partibus genitalibus. Regiomonti, 1832,
pp. 6 + 38, 3 Pls.
=Siebold, C. Th. E. von.= Ueber die Fortpflanzungsweise der
Libellulinen. (Germar’s Zeitschr. f. Ent., 1840, ii, pp. 421–438.)
=Selys-Longchamps, E. de.= Monographie des Libellulidees d’Europe. 4
Pls., 1840.
=Bassi, C. A.= Studi sulle funzioni degli organi genitali degl’
insetti da lui osservati piu specialmente nella _Bombyx mori_. (Atti
della 5 Riun. d. Scienz. Ital. Lucca, 1844, pp. 39–94.)
=Stein, F.= Vergleichende Anatomie und Physiologie der Insekten, i.
Die weiblich. Geschlechtsorgane der Käfer. Berlin, 1847, 9 Taf.
=Ormancey, P.= Recherches sur l’étui penial considéré comme limite de
l’espèce dans les coléoptères. (Ann. sc. nat., 1849, 3 sér., Zool.,
xii, pp. 227–242.)
=Roussel, C.= Recherches sur les organes génitaux des insectes
coléoptères de la famille des Scarabéides. (Compt. rend. Acad. d.
sc. Paris, 1860, l, pp. 158–161.)
=MacLachlan, R.= A monographic revision and synopsis of the
Trichoptera of the European fauna. London, 1874–80, 59 Pls.
—— On the sexual apparatus of the male Acentropus. (Trans. Ent. Soc.
London, 1872, pp. 157–162.)
=Thomson, C. G.= Nagra anmarkningar ofver arterna af slagtet Carabus.
(Thomson’s Opuscula Entomologica, vii, 1857, pp. 615–729, 1 Pl.)
=Dufour, L.= Sur l’appareil génital male du _Coræbus bifasciatus_.
(Thomson, Archiv ent., 1857, i, pp. 378–381.)
=White, F. Buchanan.= On the male genital armature in the Rhopalocera.
(Trans. Linn. Soc., ser. 1, Zool., i, pp. 357–369, 1876, 3 Pls.)
=Graber, V.= Die Aehnlichkeit im Baue der ausseren weiblichen
Geschlechtsorgane bei den Lokustiden und Akridiern auf Grund ihrer
Entwicklungsgeschichte. (Sitzber. k. Akad. d. Wissensch. Wien.,
1870, lxi, pp. 1–20, 1 Taf.)
=Scudder, Samuel H., and Edward Burgess.= On asymmetry in the
appendages of hexapod insects, especially as illustrated in the
lepidopterous genus Nisoniades. (Proc. Boston Soc. Nat. Hist., 1871,
xiii, pp. 282–306.)
=Chadima, J.= Ueber die Homologie zwischen den männlichen und
weiblichen ausseren Sexualorganen der Orthoptera Saltatoria Latr.
(Mitteil. d. naturwiss. Vereins f. Steiermark, 1872, pp. 25–33, 1
Taf.)
=Hagens, von.= Ueber die Genitalien der männlichen Bienen, besonders
der Gattung Sphecodes. (Berlin Ent. Zeitschr., 1874, pp. 25–43.)
—— Ueber die männlichen Genitalien der Bienengattung Sphecodes.
(Deutschen Entom. Zeitschr., 1882, pp. 209–228, 2 Taf.)
=Lindenman, C.= Vergleichend-anatomische Untersuchung ueber das
männliche Begattungsglied der Borkenkäfer. (Bull. Soc. Imp. d.
Natural. Moscou, 1875–77.)
=Forel, A.= Der Giftapparat und die Analdrüsen der Ameisen. (Zeitschr.
f. wiss. Zoologie, xxx, suppl., 1878.)
=Kraatz, G.= Ueber die Wichtigkeit der Untersuchung des
männlichen Begattungsgliedes der Käfer für die Systematik und
Artunterscheidung. (Deutschen Entom. Zeitschr., 1881, xxv, pp.
113–126.)
—— Ueber das männliche Begattungsglied der europaischen Cetoniiden und
seine Verwendbarkeit für deren scharfe spezifische Unterscheidung.
(Ibid., pp. 129–149.)
=Gosse, Ph. H.= On the clasping-organs ancillary to generation in
certain groups of the Lepidoptera. (Trans. Linn. Soc., 1882, Ser. 2,
Zool., ii, pp. 265–345, 8 Pls.)
—— The prehensors of male butterflies of the genera Ornithoptera and
Papilio. (Proc. Roy. Soc. London, 1881, xxxiii, pp. 23–27.)
=Radoszkowski, O.= Revision des armures copulatrices des males du
genre Bombus. (Bull. Soc. Natur. Moscou, 1884, xlix, pp. 51–92, 4
Pls.)
—— Revision des armures copulatrices des males de la tribu
Philérémides. (Ibid., 1885, lxi, pp. 359–370, 2 Pls.)
—— Revision des armures copulatrices des males de la famille des
Mutillidæ. (Horæ Soc. Ent. Ross., 1885, xix, pp. 3–49, 9 Pls.)
—— Revision des armures copulatrices des males de la tribu des
Chrysides. (Horæ Soc. Ent. Ross, xxiii, 1890, pp. 3–40, 6 Pls.)
=Hofmann, O.= Beiträge zur Kenntnis der Butaliden. (Stett. Ent. Zeit.,
1888, pp. 335–347, 1 Taf.)
=Driedzichi, H.= Revue des espèces européennes du genre Phronia Winn.
(Horæ Soc. Ent. Ross., 1889, xxiii, pp. 404–532, 10 Pls.)
=Sharp, David.= On the structure of the terminal segment in some male
Hemiptera. (Trans. Ent. Soc. London, 1890, pp. 399–427, 3 Pls.)
=Escherich, K.= Die biologische bedeutung der Genitalanhänge der
Insekten. (Verhandl. d. zool. bot. Ges. Wien., 1892.)
—— Anatomische Studien über das männliche Genitalsystem der
Coleopteren. (Zeits. f. wissens. Zool., lvii, pp. 620–641, 1 Taf., 3
figs.)
=Verhoeff, C.= Zur vergleichenden Morphologie der “Abdominalanhänge”
der Coleopteren. (Ent. Nachr., xx, pp. 93–96, 1894. Compare also O.
Schwarz and J. Weise’s criticisms in D. Ent. Zeit., pp. 153–157;
also pp. 101–109, 155–157. Zool. Anzeiger, pp. 100–106, 1894.)
—— Vergleichende—morphologische Untersuchungen ueber das Abdomen
der Endomychiden, etc., und über die Musculature des
Copulationsapparates von Triplax. (Archiv f. Naturg., lxi, pp.
213–287, 2 Taf., 1895.)
—— Vergleichende Untersuchungen über die abdominal Segmente der
weiblichen Hemiptera-Heteroptera und Homoptera. (Verh. Nat. Ver.
Bonn, l, pp. 307–374, 1894.)
=Verhoeff, C.= Beiträge zur vergleichenden Morphologie des Abdomens
der Coccinelliden, etc. (Archiv f. Naturg., lxi, pp. 1–80, 6 figs.,
1895.)
=Boas, J. E. V.= Organe copulateur et accouplement der hanneton.
(Oversigt over det K. Danske Vidensk. Selskab Forhand, 1892,
Copenhagen, 1893, 1 Pl., pp. 239–261.)
=Pérez, J.= De l’organe copulateur mâle des Hyménoptères et de sa
valeur taxonomique. (Ann. Soc. Ent. France, lxiii, pp. 74–81, Figs.,
1894.)
=Goddard, Martha Freeman.= On the second abdominal segment in a few
Libellulidæ. (Proc. Amer. Philos. Soc., xxxv, pp. 205–212, January
11, 1897, 2 Pls.)
Also the writings of Eaton, Emery, Fischer, Forel, Géhin, Godart,
Hagen, Joly, Koletani, Loew, Meinert, Mik, Nicolet, Osten Sacken,
Pictet, Roussel, Schaeffer (1754), Schaum, Schenk, J. B. Smith,
Thompson, Buchanan-White, Brunner von Wattle-Wyll, Weise, Wyenbergh.
The subject of copulation has been treated by Hoffer, Hartig,
Schiedeknecht, Verhoeff, etc.
THE ARMATURE OF INSECTS: SETÆ, HAIRS, SCALES, TUBERCLES, ETC.
[Illustration:
FIG. 208.—Larva of _Dryocampa rubicunda_, stage II.—Bridgham _del._
]
=The cuticula.=—The integument is externally either smooth and shining
or variously punctured, granulated, tuberculated, striated, or hairy. In
certain orders the skin is clothed with flattened setæ or scales, while
many forms, as some caterpillars (Figs. 208, 209), beetles (Fig. 210),
etc., are protected by spines, horns, etc., these in adult insects often
forming secondary sexual characters, usually being more developed in the
males than in the females.
[Illustration:
FIG. 209.—Larva of _Hyperchiria io_, on hatching.
]
The cuticula is not always smooth, but is often finely granulated or
even minutely spinulated. On the abdominal segments of Anabrus, as
observed by Minot, the cuticula is armed with microscopic conical
nodules scattered irregularly over it. They do not correspond, he
says, in any way to hairs; for they do not rest over pores, nor did
he see any specially modified cells underlying them. “As far as I
have observed, they are mere local irregularities, each nodule being
apparently supported by some four or six unmodified epidermal
cells.” Minot adds that the whole of the cuticula, except the cones
just described and the hairs, is divided into numerous minute
fields, each of which corresponds to a single cell of the underlying
hypodermis. Each field is bounded by a distinct polygonal outline,
and its surface is either covered by a large number of extremely
minute projecting points, as on the dorsal arch of the segment, or
is smooth, as upon the articular membrane and ventral arch. Upon the
sides of the dorsal arch and upon the spiracular membrane each field
has a projecting spine or sometimes two or even three. (See also pp.
28, 30.)
[Illustration:
FIG. 210.—_Phanæus pegasus_, ♂, from Mexico.—After Graber.
]
[Illustration:
FIG. 211.—Section of integument of _Datana ministra_: _c_, cuticula;
_hyp_, hypodermis; _p_, outer pigmented nodulated layer.
]
The cuticle of lepidopterous larvæ has also been described and
figured by Minot. In the caterpillars of different groups
investigated by him, the cuticle was found to be rough with
microscopic teeth or spinules, erect or flattened and scale-like,
and either densely crowded or scattered, and affording excellent
generic and specific characters. In the slug-worms (Limacodids) we
have observed that the cuticula is unusually rough, especially on
the spiniferous tubercle of Empretia, Parasa, etc. (Fig. 213, _c_).
The skin of the body between the tubercles is seen to be finely
shagreened, due to the presence of fine teeth, which are more or
less curved and bent, these teeth arising from a very finely
granulated surface (_d_). The cuticle of neuropterous,
trichopterous, and tenthredinid larvæ will probably afford similar
cases. The integument of the larva of Datana is, on the black bands,
rough and nodulated, the irregular nodules being filled with a black
pigment, and forming a layer (_p_) external to the true cuticula
(Fig. 211).
[Illustration:
FIG. 212.—Hairs of Datana: _f_, formative hair-cell; _c_, cuticula;
_p_, pigmented layer; _hy_, hypodermis.
]
The integument of many insects contains fine canals passing through the
chitinous layers and opening externally in minute pores. Certain of the
pore-canals communicate with hollow setæ which sit directly over the
pores; other pores form the external openings of dermal glands, but in
many cases they are empty or only filled with air, and do not have any
hairs connected with them. Each of these pores communicates with a
hair-forming hypodermal cell, called by Graber a _trichogen_.
=Setæ= (“hairs” and bristles).—The setæ of insects are, as in worms,
processes of the cuticle originating from certain of the hypodermal
cells. They arise either from a ring-like pit, or from a minute
tubercle, and are usually situated at the outlet of a pore-canal, which
connects with an underlying cell of the hypodermis (Fig. 212). They are,
then, bristle or hair-like processes arising from the hypodermis. Where
the hairs or setæ are rubbed off, their site is indicated by a minute
ring like a follicle in the chitinous integument. The cuticular hair,
says Leydig, is in its first condition the secretion of the cellular
element of the skin, and a thread-like continuation of the cell-body may
rise up through the pore-canal into the centre of the hair, remaining
there permanently.
While the setæ are usually simple, they are often branched, plumose, or
spinulose, as in larval Hemerobiidæ, Anthrenus, and Dermestes, the larvæ
of certain coccinellid beetles, notably Epilachna, and of Cassida, the
larvæ of arctians, etc., and in bees (Anthophila, Megachile, Osmia,
Colletes, Apis, etc.).
The use of these spinulose, plumose, and twisted hairs in the bees is
clearly shown by J. B. Smith, who states that as these insects walk over
flowers, the pollen grains adhere to the vestiture, “and this also
accounts for the fact, probably noticed by every observant fruit-grower,
that bees frequently bury themselves completely in the blossoms, or roll
over every part of them. Such insects are after pollen, not honey, and
by so rolling about, the pollen grains are brought into contact with and
adhere to the surface of the insect.” The syrphid flies also pollenize
flowers, the pollenizing of chrysanthemums being effected, as Smith
states, by _Eristalis tenax_, and he adds that the body vestiture of the
syrphids “is often composed of spurred and branched hairs.” (For
reference to gathering hairs, see p. 45.)
[Illustration:
FIG. 213.—Cuticular spinules of larva of Adoneta: _a_, _b_, _c_, _d_,
different forms; _e_, _e′_, caltrops.
]
Certain remarkable spines occur in limacodid larvæ, notably Empretia and
Adoneta. These we have called caltrops spines, from their resemblance to
the caltrops formerly used in repelling the attacks of cavalry. They are
largely concerned in producing the poisonous and irritating effects
resulting from contact with the caterpillars of these moths, and are
situated in scattered groups near the end of the tubercles. A group of
three is represented at Fig. 213, _e_. They are not firmly embedded in
the cuticle, but on the contrary appear to become very easily loosened
and detached, and they probably, when brought into contact with the skin
of any aggressor, burrow underneath, and are probably in part the cause
of the continual itching and annoyance occasioned by these creatures. It
will be seen by reference to Fig. 213, _e′_, that the body of the spine
is spherical, with one large, elongated, conical spine arising from it,
the spherical base being beset with a number of minute, somewhat obtuse
spinules.
[Illustration:
FIG. 214.—Glandular hairs of caterpillars. _A_, _Dasylophia anguina_:
_a_, of body; _b_, of head; _c_, of prothoracic shield. _B_,
_Ceratosia tricolor_: _a_, on body; _b_, on abdominal legs. _C_,
_Schizura ipomeæ_: _a_, from third thoracic segment; _b_, from larva
stage II; _c_, simple setæ from minute warts.
]
=Glandular hairs and spines.=—In some insects occur fine, minute, hollow
setæ from which exude, perhaps through pore-canals of extreme fineness,
droplets of a clear watery or plasma-like sticky fluid. The club-shaped
tenent hairs of the feet of Collembola, and the hairs fringing the feet
of Diptera, are modified glandular hairs. Here they serve to give out a
sticky fluid enabling the insect to walk on smooth surfaces; they end in
a vesicle-like bulbous expansion, which may contain numerous
pore-canals. Those of caterpillars were first noticed by Zeller, and
Dimmock has particularly described those of the larvæ of Pterophoridæ.
They are either club-shaped, or variously forked at the end (Fig. 214,
_B_, _a_). They are usually replaced after the first larval moult by
ordinary, simple, solid, pointed setæ, and their use in caterpillars is
as yet unknown. Whether these hairs, as seems most probable, arise from
a specialized glandular hypodermal cell, or not, has not yet been
discovered.
[Illustration:
FIG. 215.—_A_, group of setæ arising from a subdorsal tubercle: _cut_,
the cuticle; _hy_, the hypodermis; _sc_, the enlarged and
specialized cells of the hypodermis which secrete the spines
themselves; _pglc_, the nuclei which secrete the venomous fluid
which fills the cavity of the seta (_s_), seen at _p_ in a broken
spine. _B_, a short entire, and a long broken seta (_s-p_); _pgle_,
four poison cells; _p_, the poison in the hollow of the spine.
]
These temporary fine glandular hairs are probably the homologues of the
larger true glandular bristles and spines of the later stages of certain
lepidopterous larvæ, which are brightly colored and lead an exposed
life, living through a large part of the summer. In these structures the
bristles or spines are hollow, filled with a poisonous secretion formed
in a single large, or several smaller specialized hypodermal cells
situated under the base of the spine. In the venomous spines of _Lagoa
crispata_ the poisonous fluid in the larger spines (Figs. 215, _C_, 216,
_b_) is secreted in several large cells situated at the base of the
spine, and this is the usual form. In the finer spines of a large
tubercle (Figs. 215, _A_, 216) there appears to be a differentiation of
the hypodermal cells into two kinds, the large, basal deep-seated,
setigenous cells (216, _sc_) and the poison-secreting nuclei (216,
_pglc_) situated nearer the base of the setæ. The spines being filled
with poison and breaking into bits in the skin of the hands or neck,
cause great irritation and smarting. These nettling or poisonous hairs
or spines are especially venomous in the larva of Orgyia, _Empretia
stimulea_, _Hyperchiria io_, the larvæ of the saturnians (Fig. 217) and
lasiocampids, etc. They rarely occur in insects of other orders, though
the skin of Telephorus is said by Leydig to bear glandular hairs.
[Illustration:
FIG. 216.—Section of a subdorsal tubercle from a larva in stage 1:
_sc_, the setigenous cells, one for each seta; _pglc_, nuclei by
which the poison is secreted; _s_, seta; _p_, poison in middle of a
broken spine; _cut_, cuticle; _sd_, _tub_, spinulated surface of the
subdorsal tubercle.
]
Leydig states that in the stout bristles of Saturnia there is, as in
the integument of the body, a homogeneous cuticula, under which is
the cellular matrix (hypodermis), and the clear contents
(hyaloplasma) are secreted from the blood. The cell-structure of the
hairs consist, as in the cells of the body, of spongioplasma and
hyaloplasma. Leydig has observed the droplets of the secretion of
the caterpillar of _Saturnia carpini_ oozing through distinctly
observable pores, and states that there are similar openings in the
hairs and scales. Dewitz found easily observable openings at the end
of the hair of a large exotic weevil (Fig. 130).
The advanced nymph of Psylla is also armed with clavate glandular
hairs (Fig. 178).
[Illustration:
FIG. 217.—Armature of last four segments of _Callosamia promethea_:
_a_, a dorsal seta; _b_, one showing the poison (_p_) within.
]
The tubercles are outgrowths of the body-walls; they are either
smooth, warty, or spiny, as in many caterpillars. While the armature
of insects is of little morphological importance, it is evidently of
great biological importance, the welfare or even the life of the
insect depending upon it; and it varies in each species of insect,
especially in Diptera, where the position of even a single seta
characterizes the species.
[Illustration:
FIG. 218.—Section through an antennal pectination of _Saturnia
carpini_: _a_, hypodermis, formative cells of the hairs (_c_); _d_,
cuticula; _e_, trachea.—After Semper.
]
[Illustration:
FIG. 219.—Flattened hairs from the lateral tufts of larva of
_Gastropacha americana_: _A_, three from the lateral tuft of
_Heteropacha rileyana_.
]
The mode of development of the hairs was first described by Semper. In
the pectination of the antenna of _Saturnia carpini_ he observed that
the hairs arise, like the scales of the wings, from large round
formative-cells lying in the cavity, which send out through the
hypodermis and cuticle a long slender process which finally becomes the
hair (Fig. 218).
Tactile hairs are those setæ arising over nerve cells or nerve
terminations and will be discussed under the organs of sense.
[Illustration:
FIG. 220.—The same in _G. quercifolia_: _a_, a small hair ending in
two minute processes.
]
=Scales.=—In very rare cases the hairs of caterpillars (Fig. 219) are
flattened and scale-like, and this passage in the same insect of
cylindrical hairs into flattened scale-like ones, shows that the scales
are only modified hairs. Also, as we shall see farther on, Semper has
proved that their mode of origin is identical. While true scales are
characteristic of Synaptera (Thysanura and Colembola), as well as
Lepidoptera and Trichoptera, they also occur in the Psocidæ
(Amphientomum), in many Coleoptera (Curculionidæ, Cleridæ, Ptinidæ,
Dermestidæ, Byrrhidæ, Scarabæidæ, Elateridæ, and Cerambycidæ), and in
the Culicidæ, and a few other Diptera, though they are especially
characteristic of the Lepidoptera, not a species of this great order
being known to be entirely destitute of them.
[Illustration:
FIG. 221.—Flattened and spinulated hairs of tufts of larva of
_Acronycta hastulifera_.
]
[Illustration:
FIG. 222.—Scales from dorsal tuft, on second thoracic segment of larva
of _Gastropacha quercifolia_.
]
The scales vary much in shape, but are more or less tile-like, attached
to the surface of the body or wing by a short slender pedicel, and are
more loosely connected with the integument than the hairs, which are
thicker at the base or insertion than beyond.
The markings of the scales, both of Synaptera and Lepidoptera, are very
elaborate, consisting of raised lines, ridges, or striæ with transverse
ridges between. “The striæ of the transparent scales of Micropteryx are
from about 500 to 300 to the millimetre, varying in different species.
The opaque scales of Morpho, which show metallic reflections, have about
1400 striæ to the millimetre.” (Kellogg.)
The primary use of scales, as observed by Kellogg, is to protect the
body, as seen in Synaptera and Lepidoptera. A nearly as important use is
the production of colors and patterns of colors and markings, while in
certain butterflies certain scales function as the external openings of
dermal scent-glands, and they afford in some cases (as first claimed by
Kettelhoit in 1860) generic and specific characters. Spuler has shown
that the scales are strengthened by internal chitinous pillars. Burgess
has observed in the scales of _Danais plexippus_ that the under surface
of the scales is usually smooth, or provided with few and poorly
developed ridges, and this has been confirmed by Spuler and by Mayer
(Fig. 226).
In the irised and metallic scales the ridges, says Spuler, are not
divided into teeth, and they converge at the base to the pedicel and
also toward the end of the scale (Micropteryx), or end in a single
process beyond the middle (the brass-colored scales of _Plusia
chrysitis_).
The arrangement of the scales on the wings is, in the generalized moths,
irregular; in the more specialized forms they are arranged in bands
forming groups, and in the most specialized Lepidoptera they are more
thickly crowded, overlapping each other and inserted in regular rows
crossing the wings, these rows either uniting with each other or running
parallel. (Spuler.) The scattered irregular arrangement seen in
Micropteryx is also characteristic of the Trichoptera and of
Amphientomum.
[Illustration:
FIG. 223.—Portion of a longitudinal section through one of the young
pupal wings of a summer pupa of _Vanessa antiopa_: _s_, young scale;
_leu. cy._, leucocyte; _mbr. pr._, ground membrane; _prc_,
hypodermis-cells.
]
[Illustration:
FIG. 224.—Portion of a longitudinal section through one wall only of
the pupal wing of a specimen slightly older than that of Fig. 223;
_s_, older scale.
]
=Development of the scales.=—The mode of origin of the scales was first
worked out by Semper in 1886, who stated that in the wing of the pupal
Sphinx and Saturnia they are seen, in sections, to arise from large
roundish cells just under the hypodermis and which have a projection
which passes out between the hypodermis (his “epidermis”) cells,
expanding into a more or less spherical vesicle, the latter being the
first indication of the future scale. He observed that the scales are
not all formed at once, but arise one after another, so that on one and
the same wing the scales are in different stages of development.
[Illustration:
FIG. 225.—Portion of a longitudinal section through a pupal wing about
eight days before emergence: _s_, formative scale-cell; upper _s_, a
scale.
]
More recently Schaeffer has stated that the scales and also the hairs
are evaginations of greatly enlarged hypodermis cells, and still more
complete evidence has been afforded by A. G. Mayer (1896). In the wings
of Lepidoptera, about three weeks before the imago emerges, certain of
the hypodermis cells, which occur at regular intervals, begin to
increase in size and to project slightly above the level of the
hypodermis; these are Semper’s “formative cells,” and are destined to
secrete the scales. They increase in length, and appear as in Fig. 223.
In the next stage observed, the projections are much longer (Fig. 224).
The hypodermis is now thrown up into a regular series of ridges, which
run across the wing. Each ridge, says Mayer, corresponds in position
with a row of formative cells, and each furrow with the interval between
two adjacent rows. The scales always project from the tops of these
ridges. The ground or basal membrane has not participated in this
folding, and the deep processes of the hypodermis (_prc_) that once
extended to this membrane have largely disappeared. Figure 225
represents a more advanced stage almost eight days before the emergence
of the imago.
The scales are originally filled with protoplasm, which gradually
withdraws, leaving behind it little chitinous bars or pillars which
serve to bind together the upper and lower surfaces of the scales, and
finally the scales become “merely little flattened hollow sacs
containing only air.” As Mayer shows (Figs. 226, 227), from the study of
scales examined four days before emergence of the butterfly (Danais),
“the striations upon the upper surface of the scale are due to a series
of parallel longitudinal ridges,” while the under side is usually
smooth.
The mode of insertion is seen in Fig. 227. The narrow cylindrical
pedicel of the scale is merely, according to Semper, inserted into a
minute close-fitting socket, which perforates the wing-membrane, and not
into a tube, as Landois supposed. Spuler describes a sort of double sac
structure or follicle (_Schuppenbalg)_ which receives the hollow pedicel
of the scale. This was originally (1860) observed by F. J. Carl Mayer,
but more fully examined by Spuler (Fig. 228) though not detected by A.
G. Mayer.
[Illustration:
FIG. 226.—Portion of a cross-section through the pupal wing of _Danais
plexippus_, about six days before emergence: _sg_, scale; _cta.al_,
wing-membrane; _cl.frm_, formative cell of the scale; _mbr.pr_,
ground-membrane; _fbr.h′drm_, hypodermal fibres of pupal wings. _A_,
portion of a longitudinal section through the pupal wing, eight or
nine days before emergence; _prc_, processes of young hypodermis
scales.—This and Figs. 223–225 after Mayer.
]
=Spinules, hair-scales, hair-fields, and androconia.=—Besides the
scales, fine spinules occur on the thickened veins of the wings of the
Blattidæ, where they resemble fir-cones; also in the Perlidæ, in the
Trichoptera, and in the more generalized Lepidoptera (Micropterygidæ and
Hepialidæ), occur, as indicated by Spuler, delicate chitinous hollow
spinules scarcely one-tenth as long as, and more numerous than, the
scales, which sometimes form what he calls “Haftfelds,” or holding
areas. These spinules have also been noticed by Kellogg, and by myself
in Micropteryx; Kellogg, and also Spuler, have observed them in certain
Trichoptera (Hydropsyche). These also occur on the veins, and detached
ones near large one-jointed hairs, or hair-scales, said by Kellogg to be
striated. Kellogg has detected these scale-hairs, as he calls them, in
Panorpa.
[Illustration:
FIG. 227.—View looking down upon the upper (_i.e._ exposed) surface of
one of the large scales situated on the veins of _Danais plexippus_,
about four days before emergence: _clm_, chitinous pillars found in
scales. _A_, _a_ smaller scale, _a_, _a′_, sections of the scales.
_B_, leucocyte found in the larger scale.—After Mayer.
]
[Illustration:
FIG. 228.—Scale-follicles: _A_, of a scale of _Galleria mellonella_:
_r_, neck-ring. _B_, the same of _Polyommatus phlæas_. _C_, the same
of a hair on inner edge of hind wing of _Lycæna alexis_ ♀.—After
Spuler.
]
[Illustration:
FIG. 229.—_A_, portion of wing of a caddis-fly (Mystacides). _B_,
enlarged, showing the androconia and hair-scales. _C_, a separate
androconium.—After Kellogg.
]
The “hair-scales” of the phylogenetically older Trichoptera correspond
to certain scales of Lepidoptera, especially the Psychidæ (Spuler),
variously called “plumules” (Deschamps), “battledore scales,” also
certain minute cylindrical hairs. To these scent-scales is applied the
term _androconia_. They are found, almost without exception, on the
upper side of the fore wings, occurring in limited areas, such as the
discal spots, or on folds of the wings. Fritz Müller has shown that they
function as scent-scales, and are confined to the males. Kellogg has
detected androconia-like scales on the wings of a caddis-fly,
_Mystacides punctata_ (Fig. 229).
[Illustration:
FIG. 280.—Cross-section of androconia surface on wing of _Thecla
calanus_; _a_, androconia; _gl_, gland of base; _s_, ordinary
scales; _w_, wing in section.—After Thomas.
]
Thomas has proved by sections of the wing of Danais, etc., that the
androconia arise from glands situated in a fold of the wing (Fig. 230),
and he states that the material elaborated by the local glands, and
distributed upon the surface of the wing by the androconia, is that
which gives to many of the Lepidoptera their characteristic odor. On
comparing these “glands,” it is evident that they are groups of
specialized formative cells of Semper (trichogens), which secrete an
odorous fluid, issuing perhaps from extremely fine pore-canals at the
ends of the androconia. They thus correspond to the glandular hairs,
poison-hairs, and spines of caterpillars, the formative cells of which
contain either a clear lymph or poison.
LITERATURE
_a._ Hairs, bristles, cleaning spines, calcaria, combs, etc.
=Leydig, Franz.= Zum feineren Bau der Arthropoden. (Müller’s Archiv f.
Anat. und Phys., 1855, pp. 376–480.)
=Fobel, Auguste.= Les fourmis de la Suisse. Bâle, 1874.
=Saunders, Edward.= Remarks on the hairs of some of our British
Hymenoptera. (Trans. Ent. Soc. London, 1878, pp. 169–171.)
=Perez, J.= Notes d’apiculture. (Bull. Soc. d’Apic. de la Gironde,
Bordeaux, 1882.)
=Osten Sacken, C. R. von.= An essay on comparative chætotaxy, or the
arrangement of characteristic bristles of Diptera. (Trans. Ent. Soc.
London, 1884, pp. 497–517.)
—— Preliminary notice of a subdivision of the suborder Orthorrhapha
Brachycera (Diptera) on chætotactic principles. (Berlin Ent.
Zeitschr., 1896, pp. 365–373.)
=Janet, Charles.= Études sur les fourmis. 8^e Note. Sur l’organe de
nettoyage tibio-tarsien de _Myrmica rubra_. (Ann. Soc. Ent. France,
1895, pp. 691–704, 6 Figs.)
See also J. B. Smith’s Economic Entomology, 1896, hairs of bees. Also
the writings of De Geer, Huber, Fenger, Mayr, Forel, Canestrini, and
Berlese (1880); Dahl, Cheshire, etc.
_b._ Glandular and poisonous setæ and spines
=Ratzeburg, J. Th. Ch.= Ueber entomologische Krankheiten. (Stettin
Ent. Zeit., 1846, vii, pp. 35–41.)
=Zeller, P. C.= Revision der Pterophoriden. (Linnæa Ent., vi, pp.
319–416, 1852, at p. 356 speaks of “Drüsenhärchen.”)
=Dimmock, George.= On some glands which open externally on insects.
(Psyche, iii, pp. 387–401, 1882.)
=Goossens, Th.= Des chenilles urticants. (Ann. Soc. Ent. France, 1881,
pp. 231–236.) Des chenilles vésicants. (Ibid., 1886, pp. 461–464.)
=Packard, A. S.= Notes on some points in the external structure and
phylogeny of insects. (Proc. Boston Soc. Nat. Hist., xxv, 1890, pp.
83–114, 2 Pls.)
—— A study of the transformations and anatomy of _Lagoa crispata_, a
bombycine moth. (Proc. Amer. Phil. Soc., xxxii, pp. 275–292, 7 Pls.,
1894.)
=Holmgren, Emil.= Studier öfner hudens och de körtelartade hudorganens
morfologi hos Skandinaviska macrolepidopterlarver. (K. Svenska
Vetenskaps-Akad. Handl., xxvii, pp. 1–83, Stockholm, 1895, 9 Pls.)
Also the writings of Leydig, Keller, Bach, Karsten, Scribner, Riley,
etc.
(See also Literature of repugnatorial glands.)
_c._ Androconia
=Deschamps, Bernard.= Récherches microscopiques sur l’organisation des
ailes der Lépidoptères. (Ann. des Sc. nat. [?], iii, pp. 111–157,
1835.)
=Waufor, T. W.= On certain butterfly scales characteristic of sex.
(London, 1867–68.)
=McIntire, S. J.= Notes on the minute structure of the scales of
certain insects. (London, 1871.)
=Anthony, J.= The markings on the battledore scales of some of the
Lepidoptera. (London, 1872.)
=Scudder, S. H.= Antigeny or sexual dimorphism in butterflies. (Proc.
Amer. Acad. Arts and Sc., xii, 1877, pp. 150–158.) Also Butterflies,
etc. (New York, 1881, pp. 192–206, figs.)
=Müller, Fritz.= A prega costal das Hesperideas. (Archivas do Museo
nac. do Rio de Janeiro, iii, pp. 41–50, 2 Pls., 1878.)
=Thomas, M. B.= The androconia of Lepidoptera. (Amer. Nat., xxvii, pp.
1018–1021, 2 Pls., 1893.)
_d._ Scales
=Leydig, Franz.= Zum feineren Bau der Arthropoden. (Archiv f. Anat.
und Phys., 1855, pp. 376–480, 1 Taf.)
=Semper, Carl.= Beobachtungen über die Bildung der Flügel, Schuppen,
und Haare bei den Lepidopteren. (Zeitschrift f. wissensch. Zoologie,
1857, pp. 326–339, 1 Taf.)
=Mayer, F. T. Karl.= Ueber den Staub der Schmetterlingsflügel.
(Allgem. mediz. Centralzeitung, 1860, pp. 772–774.)
=Landois, H.= Beiträge zur Entwicklungsgeschichte der
Schmetterlingsflügel in der Raupe und Puppe. (Zeitschr. f.
wissensch. Zoologie, xxi, 1871, pp. 305–316, 1 Taf.)
=Weismann, August.= Ueber Duftschuppen. (Zool. Anzeiger, i, 1878, pp.
98–99.)
=Dimmock, George.= Scales of Coleoptera. (Psyche, iv, pp. 1–11, 23–27,
43–47, 63–71, 1883.)
=Schaeffer, Cäsar.= Beiträge zur Histologie der Insekten. (Zool.
Jahrbücher, Abth. f. Anat. u. Ontog., iii, pp. 611–652, 2 Pls.,
1889.)
=Kellogg, Vernon L.= The taxonomic value of the scales of the
Lepidoptera. (Kansas Univ. Quart., iii, pp. 45–89, figs. 1–17, 9
Taf., 1894.)
=Mayer, Alfred G.= The development of the wing-scales and their
pigment in butterflies and moths. (Bull. Mus. Comp. Zool., xxix.,
1896, pp. 209–236, 7 Pls.)
=Spuler, Arnold.= Beiträge zur Kenntniss des feineren Baues und der
Phylogenie der Flügeltedeckung der Schmetterlings. (Zool. Jahrb.
Abth. f. Anat. u. Ontog., viii, pp. 520–543, 1 Taf., 1895.)
—— Ueber das Vorhandensein von Schuppenbalg bei den Schmetterlingen.
(Biol. Centralblatt, xvi, Sept. 15, 1896, pp. 677–679, 3 figs.)
THE COLORS OF INSECTS
The colors and bright markings of insects, especially those of
butterflies, render them the most brilliant and beautiful creatures in
existence, rivalling and even excelling the gay hues of our most
splendidly colored birds. The subject has been but recently taken up and
is in a somewhat crude condition, but the leading features have been
roughly sketched out by the work of a few observers from a physical,
chemical, and biological point of view.
The colors of insects, as of all other animals, are primarily due to the
action of light and air; other factors are, as Hagen observes, heat and
cold, moisture and dryness, as recently shown by the experiments on
butterflies by Dorfmeister, Weismann, W. H. Edwards, and later
observers. They have their seat in the integument. Hagen divides colors
into optical and natural.
=Optical colors.=—“These,” says Hagen, “are produced by the interference
of light, and are by no means rare among insects, but they are solely
optical phenomena. Colors by the interference of light are produced in
two different ways: either by thin superposed lamellæ, or by many very
fine lines or small impressions in very close juxtaposition.
“1. There must be present at least two superposed lamellæ to produce
colors by interference. The naked wings of Diptera, of dragon-flies, and
of certain Neuroptera often show beautiful interference colors. The
wings of Chrysopa and Agrion show interference colors only for a certain
time, viz., as long as the membranes of the wings are soft and not
firmly glued together. Afterwards such wings become simply hyaline.
“The scales of Entimus and other Curculionidæ are well known for
their brilliancy, and it is interesting to remark that when dry
scales are examined with the microscope, many are found partly
injured, which give in different places different colors, according
to the number of layers which remain. The elytra of some
Chrysomelina and other beetles with iridescent colors probably
belong to the same category.
“2. When there are scales with many fine lines or small impressions
close to each other, we have the second mode of producing colors.
“The fine longitudinal and transversal lines of lepidopterous scales
seem to serve admirably well to produce the brilliant effect of
color-changing butterflies. But there must be something more present, as
most of the scales of Lepidoptera are provided with similarly fine
lines, and only comparatively few species change colors. I remark
purposely that the lines in the color-changing scales are not in nearer
juxtaposition.” (Hagen.)
“The colors of butterflies change mostly from purple to blue,
sometimes to yellow. The splendid violet color at the end of the
wings of _Callosune ione_ is brought out by a combination of the
natural with interference colors. Originally the scales are colored
lake-red; but a blue interference color is mixed with it; hence the
violet hue results. The blue tones, _i.e._ the splendid varying blue
of the Morpho butterflies, Schatz claims, owe their hue less to the
interference of light than to a clouded layer of scales situated
over the dark ground, through which the light becomes reflected on
the same. The scales of the Morphids are in reality brown, as we see
by transmitted light; moreover, only the upper side of the scales
sends off blue reflections—the under side is simply brown. But the
blue scales of Urvilliana are also shining blue beneath; by
transmitted light they appear as if clear yellow. The smaragd-green
scales of Priamus show by transmitted light a bright red-orange, and
the orange-yellow of Crœsus a deep grass-green.” (Schatz in Kolbe.)
“Krukenberg presumes the golden-green color of _Carabus auratus_ to
be an interference color. It is not changed by the interference of
light, nor was he able to extract from the elytra any green pigment
with ether, benzol, carbon of sulphur, chloroform, or alcohol, even
after having previously submitted the elytra to the influence of
muriatic acid or ammonia. Chlorophyll is not present, whether free
or combined with an acid.” (Hagen.)
Leydig has shown that the interference colors of the hairs of
certain worms (Aphrodite and Eunice) may be produced by very small
impressions in juxtaposition, which bring about the same effect as
striæ. Such an arrangement occurs on the feathers of birds, _i.e._
on the necks of pigeons and elsewhere, and Hagen suggests that this
kind of interference colors occurs more frequently among insects
than is commonly known. At least the limbs of certain forms appear
yellow, but when held in a certain position change to brown or
blackish. “I know of no other explanation of this not uncommon fact
on the legs of Diptera, of Hymenoptera, and of Phryganidæ.”
Interference colors, he adds, may occur in the same place together
with natural colors. “The mirror spots of _Saturnia pernyi_ show
besides the interference colors a white substance in the cells of
the matrix, which Leydig believes to be guanin. But this fact is
denied by Krukenberg for the same species and also for _Attacus
mylitta_ and _Plusia chrysitis_.”
=Natural colors.=—These are divided by Hagen into _dermal_ (cuticular)
and _hypodermal_. The dermal colors are due to pigment deposited in the
form of very small nuclei in the cuticula. Hagen considers them as
“produced mostly by oxidation or carbonization, in consequence of a
chemical process originating and accompanying the development and the
transformations of insects.”
“To a certain extent the dermal colors may have been derived from
hypodermal colors, as the cuticula is secreted by the hypodermis,
and the colors may have been changed by oxidation and air-tight
seclusion. The cuticula is in certain cases entirely colorless,—so
in the green caterpillar of _Sphinx ocellata_; but the intensely red
and black spots of the caterpillar of _Papilio machaon_ belong to
the cuticula, and only the main yellow color of the body to the
hypodermis.” (Leydig, Histiol., p. 114.)
“The dermal colors are red, brown, black, and all intermediate shades,
and all metallic colors, blue, green, bronze, copper, silver, and gold.
The dermal colors are easily to be recognized as such, because they are
persistent, never becoming obliterated or changed after death.” (Hagen.)
Minot and Burgess refer to the cuticular colors of the cotton-worm
(Aletia), the dark brown color belonging to the cuticula or crust.
“Upon the outside of the crust is a very thin but distinct layer,
which in certain parts rises up into a great number of minute,
pointed spines that look like so many dots in a surface view. Each
spine is pigmented diffusely, and together they produce the brown
markings. The spines are clustered in little groups, one group over
each underlying hypodermal cell.” (U. S. Ent. Comm., 4th Report, p.
46.) Minot also shows that in caterpillars generally a part of the
coloration is caused by pigmentation of the cuticula.
In a dull-colored insect, such as the Mormon cricket (Anabrus), the
coloration, as Minot states, depends principally upon the pigment of
the hypodermis shining through the cuticula. “Most of the cells
contain dull, reddish-brown granules, but scattered in among them
are patches of cells bright green in color. I have observed no cells
intermediate in color; on the contrary, the passage is abrupt, a
brown or red cell lying next a green one. Indeed, I have never seen
any microscopic object more bizarre than a piece of the epidermis of
Anabrus spread out and viewed from the surface.” (2d Report U. S.
Ent. Comm., p. 189.)
The pigment may extend through the entire cuticula, but it is usually
confined to the outermost layers, and occurs there in union with a
peculiar modelling of the upper surface into microscopic figures which
are of interest not only from their delicacy, but because they vary with
each species. (See p. 184.)
The hypodermal colors, situated in the hypodermis, are, according to
Hagen, the result of a chemical process, generating color out of
substances contained in the body. They are easily recognized, since they
fade, change, and disappear after death. But where these colors are
preserved after death and enclosed in air-tight sacs, as in the elytra
and scales and hairs of the body, they persist, though, as we well know,
they may fade after exposure to light.
The hypodermal colors are mostly brighter and lighter than the dermal
ones, being light blue or green in different shades, yellow to orange,
and the numerous shades of these colors combined with white;
exceptionally they are metallic, as in Cassida, and are then obliterated
after death.
“The fact that such metallic colors can be retained in dead
specimens by putting a drop of glycerine under the elytra, leads us
to conclude that those colors are based upon fat substances. The
hypodermal colors are never glossy, as far as I know; the dermal
colors frequently.
“As the wings, elytra, and hairs all possess a cuticula, dermal
colors are frequently to be found, together with hypodermal ones,
chiefly in metallic colors. In the same place both colors may be
present, or one of them alone. So we find hypodermal colors in the
elytra of Lampyridæ. In the elytra of the Cicindelidæ the main
metallic color is dermal, the white lines or spots are hypodermal,
by which arrangement the variability in size and shape of those
spots is explained.
“There occur in a number of insects external colors, that is, colors
upon the cuticula, which I consider to be in fact displaced
hypodermal colors: the mealy pale blue or white upon the abdomen of
some Odonata, the white on many Hemiptera, the pale gray on the
elytra and on the thorax of the Goliath beetle, and the yellowish
powder on Lixus. Some of these colors dissolve easily by ether or
melt in heat, and some of them are a kind of wax. I believe that
those colors are produced in the hypodermis, and are exuded through
the pore-canals.” (Hagen.)
The white colors are simply for the most part due to the inclusion of
air in scales. The white mother-of-pearl spots of Argynnis are produced
by a system of fine transverse pore-canals filled with air; in
Hydrometra the white ventral marks have the same origin. (Leydig.)
The further statements and criticisms of Hagen regarding the relation of
color to mimicry, sexual selection, and the origin of patterns are of
much weight and will be referred to under those heads. Indeed, these
subjects cannot well be discussed without reference to the fundamental
facts stated in the masterly papers of Leydig and of Hagen, and much of
the theorizing of these latter days is ill-founded, because the colors
of insects and animals are attributed to natural selection, when they
seem really the result of the action of the primary factors of organic
evolution, such as changes of light, heat, cold, and chemical processes
dependent on the former.
As to the chemical nature of color, Hagen, after quoting the results of
Krukenberg and others, thinks that the colors of insects are chemically
produced by a combination of fats or fat-acids with other acids or
alkalis under the influence of air, light, and heat. He concludes:—
1. That some colors of insects can be changed or obliterated by acids.
2. That two natural colors, madder-lake and indigo, can be produced
artificially by the influence of acid on fat-bodies.
3. As protein bodies in insects are changed into fat-bodies, and may be
changed by acids contained in insects into fat-acids, the formation of
colors in the same manner seems probable.
4. That colors can be changed by different temperatures.
5. That the pattern is originated probably by a combination of oxygen
with the integument.
6. That mimicry of the hypodermal colors may be effected by a kind of
photographic process.
7. Finally, color and pattern are produced by physiological processes in
the interior of the bodies of insects.
Krukenberg concludes that change of color (in perfectly developed
insects) is a consequence of the change of food, and can be
explained by the alteration of the pigment through heat and light.
His experiments were made in order to ascertain the cause of the
turning of green grasshoppers in autumn into yellow and pink. He
tried to answer two questions: First, does the pigment of
grasshoppers originate directly out of the food, and does it consist
of pure chlorophyll or of a substance containing chlorophyll, or is
it to be accepted as a peculiar product of the organism? Second, is
the color the consequence of only one pigment, or of several?
Special analysis proves that the green color has no connection with
chlorophyll. He concludes: “It is evident that the green color of
the grasshopper is the consequence of several different pigments
which can be separated by a chemical process.” Krukenberg believes
that light has a marked influence on the color of insects and that
light turns to red or pink the insects which were green during the
summer. It would seem, however, more probable that cold was the
agent, the change being due to the colder autumn weather.
Here we might refer to the results of the studies of Buckton and
Sorby, on the changes in color of Aphides:—
“1. The purple coloring matter appears to be a quasi-living
principle, and not a product of a subsequent chemical oxidizing
process. Mounted in balsam or other preserving fluids, the darker
species stain the fluid a fine violet.
“2. As autumn approaches and cold weather reduces the activity of
the Aphides, the lively greens and yellows commonly become converted
into ferruginous red, and even dark brown, which last hue in reality
partakes more or less of intense violet or purple. These changes
have some analogy with the brilliant hues assumed by maple and other
leaves during the process of slow decay.
“3. Aqueous solutions of crushed dark brown and yellow-green
varieties of Aphides originate different colors with acids and
alkalies.
“4. In the generality of cases coloring-matters, such as indigo,
Indian yellow, madder-lake, and the like, do not separately exist in
the substance of vegetables, but the pigments are disengaged through
fermentation or oxygenation. Again, alizarin itself is reddish
yellow, but alkaline solutions strike it a rich violet just as we
find them to act towards the substance which Mr. Sorby calls
aphidilutein.
“5. Mr. Sorby’s four stages of the changes effected by the oxidation
of aphideine produce four different substances.”
=Chemical and physical nature of the pigment.=—Researches in this
difficult field of inquiry have been made by Landois (1864), Sorby
(1871), Meldola (1871), by Krukenberg (1884), and more recently by
Coste, Urech, Hopkins, and Mayer, and the subject is of fundamental
importance in dealing with mimicry and protective coloration, the
primary causes of which appear to be due to the action of physical and
chemical agents.
Over twenty years ago Meldola observed that the yellow pigment of the
sulphur-yellow butterfly (_Gonopteryx rhamni_) was soluble in water, and
showed that its aqueous solution had an acid reaction.
Besides the yellow uranidin found by Krukenberg in different beetles
and lepidopterous pupæ, still other coloring-matters, which are very
constant in different species are readily recognized by the
spectroscope. “Thus there appear in the brownish yellow lymph of
_Attacus pernyi_, _Callosamia promethea_ and _Telea polyphemus_,
after saponification of the precipitated soap readily effected by
ether, or incompletely or not removed by benzine, a chlorophane-like
lipochrome; and in the yellowish green lymph of _Saturnia pyri_ and
of _Platysamia cecropia_ besides this pigment still another whose
spectrum shows a broad band on D, but which disappears with the
addition of acetic acid or ammonia, as also after a long heating of
the lymph up to 66° C.”