REPRODUCTION.
_SPECIAL REFERENCES._
BRANDT, A. Ueber die Eiröhren der Blatta (Periplaneta) orientalis.
Mem. Acad. St. Petersb. Ser. 7, Vol. XXI. (1874). [Ovarian Tubes of
Cockroach.]
LACAZE-DUTHIERS. Rech. sur l’armure génitale femelle des Insectes
Orthoptères. Ann. Sci. Nat., Zool., 3^e Sér., Tom. XVII. (1852).
[External reproductive organs of female Orthoptera.]
BERLESE. Ricerde sugli organi genitali degli Ortotteri. Atti della
R. Acad. dei Lincei. Ser. 3, Vol. XI. (1882). [Genital Organs of
European Orthoptera.]
KADYI. Beitr. zur Vorgänge beim. Eierlegen der Blatta Orientalis.
Vorläufige Mittheilung. Zool. Anz., 1879, p. 632. [Formation of
egg-capsules of Cockroach.]
BREHM. Comparative structure of the reproductive organs in Blatta
germanica and Periplaneta orientalis. Mem. Soc. Ent. St. Petersb.,
Tom. VIII. (1880). In Russian. [Male organs only.]
RAJEWSKY. Ueber die Geschlechtsorgane von Blatta orientalis, &c.
Nachr. d. kais. Gesellsch. d. Moskauer Universität., Bd. XVI.
(1875). [Testes of Cockroach. The original paper is in Russian; an
abstract is given in Hofmann and Schwalbe’s Jahresbericht, 1875,
p. 425.]
BÜTSCHLI. Bau u. Entwickelung d. Samenfäden bei Insekten u.
Crustaceen. Zeits. f. wiss. Zool., Bd. XXI., pp. 402–414; 526–534.
Pl. xl. xli. (1871). [Spermatozoa and spermatogenesis in the
Cockroach.]
LA VALETTE ST. GEORGE. Spermatologische Beiträge, II.
_Blatta germanica._ Arch. f. mikr. Anat., Bd. XXVII. (1886).
[Spermatogenesis in _B. germanica_.]
MORAVITZ. Quædam ad anat. Blattæ germanicæ pertinentia. Dissertatio
inauguralis. Dorpat. (1853). [An excellent early account of the
anatomy of _B. germanica_, including a description of the male and
female organs. The figures are not trustworthy.]
_Female Reproductive Organs._
The ovaries of the two sides of the body are separated, as in most
Insects, and consist on each side of eight tubes, four dorsal and
four ventral, which open into the inner side of a common oviduct.
The two oviducts unite behind, and form a very short uterus. Tracheæ
and fat-cells tie the ovarian tubes of each side together into a
spindle-shaped bundle. Each tube is about ·4 in. long, and has a
beaded appearance, owing to the eggs which distend its elastic wall.
It gradually tapers in front; then suddenly narrows to a very small
diameter; and lastly, joins with the extremities of the other tubes
to form a slender solid filament, which passes towards the heart, and
becomes lost in the fat-body. The wall of an ovarian tube consists
of a transparent elastic membrane, lined by epithelium, and invested
externally by a peritoneal layer of connective tissue.
[Illustration: Fig. 94.--Female Reproductive Organs. _Od_, oviduct;
_CG_, colleterial gland. × 14.]
The epithelium of an ovarian tube presents some remarkable
peculiarities which disguise its true character. High up in the tube,
the narrow lumen is occupied by a clear protoplasm, in which nuclei,
but no cell walls, can be discerned. Where the tube suddenly widens,
large rounded and nucleated masses of protoplasm appear, interspersed
with nuclei entangled in a network of protoplasm. Passing down the
tube, the large cells, which can now be recognised as eggs, arrange
themselves in a single row, to the number of about twenty. They are
at first polygonal or squarish, but gradually become cylindrical, and
finally oval. Between and around the eggs the nuclei gradually arrange
themselves into one-layered follicles, which are attached, not to the
wall of the tube, but to the eggs, and travel downwards with them. As
the eggs descend, the yolk which they contain increases rapidly, and
the germinal vesicle and spot (nucleus and nucleolus), which were at
first very plain, disappear. A vitelline membrane is secreted by the
inner surface, and a chitinous chorion by the outer surface of the
egg-follicle.
[Illustration: Fig. 95.--Ovarian Tube (acetic acid preparation),
showing scattered nuclei (upper figure), which ultimately form
follicles around the ova (lower figure). Copied from Brandt, _loc.
cit._]
The lowest egg in an ovarian tube is nearly or altogether of the
full size; it is of elongate-oval figure, and slightly curved, the
convexity being turned towards the uterus. It is filled with a clear
albuminous fluid, which mainly consists of yolk. The chorion now forms
a transparent yellowish capsule, which under the microscope appears to
be divided up into very many polygonal areas, defined by rows of fine
dots. These areas probably correspond to as many follicular cells. The
convex surface of the chorion is perforated by numerous micropyles,
fine pores through which it is probable the spermatozoa gain access to
the interior of the egg.
The uterus has a muscular wall and a chitinous lining. Two repeatedly
branched colleterial glands open into its under side. Of these the
left is much the larger, and overlies the other. It consists of many
dichotomous tubes, some of which are a little dilated at their blind
ends. The gland is much entangled with fat-cells, which make it
difficult to unravel. The right gland is probably of no functional
importance; the left gland is filled with a milky substance, containing
many crystals and a coagulable fluid, out of both of which the
egg-capsule is formed.[164]
[164] The crystals have been supposed to consist of oxalate of
lime (Duchamp, Rev. des sci. nat. Montpellier, Tom. VIII.). Hallez
observes that they are prismatic, with rhombic base, the angles
truncated. They are insoluble in water and weak nitric acid, but
dissolve rapidly in strong sulphuric acid without liberation of gas,
and still more rapidly in caustic potash. (Compt. Rend., Aug., 1885.)
At its hinder end the uterus opens by a median vertical slit, which
lies in the 8th sternum, into a genital pouch which represents part
of the external integument, folded back far into the interior of the
abdomen. (See fig. 96.) Upon the dorsal wall of the genital pouch the
orifice of the spermatheca is situated.[165] This is a short tube
dilated at the end, and wound into a spiral of about one turn. From
the tube a cæcal process is given off, which may correspond with
the accessory gland attached to the duct of the spermatheca in many
Insects (_e.g._, Coleoptera, Hymenoptera, and some Lepidoptera). The
spermatheca is filled during copulation, and is always found to contain
spermatozoa in the fertile female.[166] The spermatozoa are no doubt
passed into the genital pouch from time to time, and there fertilise
the eggs descending from the ovarian tubes.
[165] It is usually stated that the spermatheca of the Cockroach
opens into the uterus, as it does in most other Insects, but this is
not true. Locusts and Grasshoppers have the outlet of the spermatheca
placed as in the Cockroach; in other European Orthoptera, it lies
upon the dorsal wall of the uterus. (Berlese, loc. cit., p. 273.)
[166] It is a striking proof of the sagacity of Malpighi, that he
should have observed in the Silkworm the spermatophore of the male
(“in spiram circumvolutum persimile semen”) and the spermatheca of
the female. His reasoning as to the function of the spermatheca
wanted nothing but microscopic evidence of the actual transference
of spermatozoa to establish it in all points. Audouin and Siebold
supplied what was wanting nearly two centuries later, but they
mistook the spirally wound spermatophore for a broken-off penis, and
Stein (Weibl. Geschlechtsorgane der Käfer, p. 85) first arrived at
the complete proof of Malpighi’s explanation.
[Illustration: Fig. 96.--Diagram to show the theoretical (upper figure)
and actual position of the hinder abdominal sterna in the female
Cockroach. _U_, uterus; _s_, spermatheca. The nerve-cord is introduced
into both figures.]
The external reproductive organs of the female Cockroach belong to the
7th, 8th, and 9th somites. The 7th sternum is incompletely divided into
anterior and posterior sections, and the posterior section is split
into lateral halves. These are joined by a flexible membrane, which
admits of the wide separation of the halves, when copulation or the
passage of the large egg-capsule renders it necessary. The vertical
faces of the membrane, which are pressed together when the parts are at
rest, are stiffened by chitinous thickenings.
If the succeeding sterna retained their proper place, as they do in
some Orthoptera (_e.g._, the Mole Cricket), the 8th and 9th sterna
would project beyond the 7th, while the rectum would open beneath the
last tergum, and the uterus between the 8th and 9th sterna. In the
adult female Cockroach, however, the 8th and 9th somites are telescoped
into the 7th, and completely hidden by it. Their terga are reduced to
narrow bands. The 8th sternum forms a semi-transparent plate which
slopes downwards and backwards, and is pierced by a vertical slit, the
outlet of the uterus. The upper edge of this sternum is hinged upon
the projecting basis of the anterior gonapophyses (to be described
immediately), and the parts form a kind of spring joint, ordinarily
closed, but capable of being opened wide upon occasion. The 9th sternum
is a small median crescentic plate, distinct from the 8th; it supports
the spermatheca, whose duct traverses an oval plate which projects from
the fore-edge of the sternum.
[Illustration: Fig. 97.--Hinder end of abdomen of female Cockroach. In
the upper figure the halves of the 7th sternum are closed; in the lower
figure they are open.]
By the telescoping of the 8th and 9th somites the sterna take the
position shown in fig. 96_B_, and a new cavity, the genital pouch, is
formed by invagination. This receives the extremity of the body of
the male during copulation, while it serves as a mould in which the
egg-capsule is cast during oviposition. Its chitinous lining resembles
that of the outer integument. The uterus opens into its anterior end,
which is bounded by the 8th sternum; the spermatheca opens into its
roof, which is supported by the 9th sternum and the gonapophyses; while
its floor is completed by the 7th sternum and the infolded chitinous
membrane.
[Illustration: Fig. 98.--External Reproductive Organs of Female. _T^8_,
&c., terga; _S^7_, &c., sterna; _G_, anterior gonapophysis; _G_′, its
base; _g_, posterior gonapophyses; _Od_, oviduct; _sp_, spermatheca;
_R_, rectum. The upper figure shows the parts in oblique profile;
the left lower figure is an oblique view from before of the outlet
of the uterus, the anterior gonapophyses being cut short; the right
lower figure shows the gonapophyses. Arrows indicate the outlet of the
oviduct and uterus.]
A pair of appendages (anterior gonapophyses) are shown by the
development of the parts to belong to the 8th somite. They are
slender, irregularly bent, and curved inwards at the tips. A small,
forked, chitinous slip connects them with both the 8th and 9th terga,
but their principal attachment is to the upper (properly, posterior)
edge of the 8th sternum. The anterior gonapophyses expand at their
bases into broad horizontal plates, which form part of the roof of the
genital pouch.
Two pairs of appendages, belonging to the 9th somite, form the
posterior gonapophyses. The outer pair are relatively large, soft, and
curved: the inner narrow, hard, and straight.[167]
[167] The descriptions and figures of the reproductive appendages of
female Orthoptera by Lacaze-Duthiers (Ann. Sci. Nat., 1852) are so
often consulted, that it may be useful to explain how we understand
and name the same parts. In pl. xi., fig. 2, 8′ and 9′ are the 8th
and 9th terga; the anterior gonapophyses are seen to be attached to
them below; _a_ (figs. 2 and 4) is the base of the same appendage,
but the twisted ends are incorrect; the 8th sternum is seen at the
back (figs. 2 and 4); _a_′ represents the outer, _f_ the inner pair
of posterior gonapophyses.
The anterior gonapophyses form the lower, and the posterior the upper
jaw of a forceps, which in many Insects can be protruded beyond the
body. Some of the parts are often armed with teeth, and the primary use
of the apparatus is to bore holes in earth or wood for the reception
of the eggs. Hence the apparatus is often called the _ovipositor_. It
forms a prominent appendage of the abdomen in such Insects as Crickets,
Saw-flies, Sirex, and Ichneumons. The sting of the Bee is a peculiar
adaptation of the same organ to a very different purpose. In the
Cockroach the ovipositor is used to grasp the egg-capsule, while it
is being formed, filled with eggs, and hardened; and the notched edge
(fig. 5, p. 23) is the imprint of the inner posterior gonapophyses,
made while the capsule is still soft. The shape of the parts in the
male and female indicates that the ovipositor is passive in copulation,
and is then raised to allow access to the spermatheca.
_Male Reproductive Organs._
The male reproductive organs of Insects, in spite of very great
superficial diversity, are reducible to a common type, which is
exemplified by certain Coleoptera. The essential parts are (1) the
_testes_, which in their simplest form are paired, convoluted tubes;
more commonly they branch into many tubules or vesiculæ, while they
may become consolidated into a single organ; (2) long coiled _vasa
deferentia_, opening into or close to (3) paired _vesiculæ seminales_,
which discharge into (4) the _ejaculatory duct_, a muscular tube, with
chitinous lining, by which the spermatozoa are forcibly expelled.
Opening into the vesiculæ seminales, the ejaculatory duct, or by a
distinct external orifice, may be found (5) _accessory glands_, very
variable in form, size, and number. More than one set may occur in the
same Insect. To these parts, which are rarely deficient, are very often
appended an external armature of hooks or claspers.
The male Cockroach will be found to agree with this description.
It presents, however, two peculiarities which are uncommon, though
not unparalleled. In the first place the testes are functional only
in the young male. They subsequently shrivel, and are functionally
replaced by the vesiculæ seminales and their appendages, where the
later transformations of the sperm-cells are effected. The atrophied
testes are nevertheless sufficiently large in the adult to be easily
made out. Secondly, the accessory glands are numerous, and differ
both in function and insertion. Two sets are attached to the vesiculæ
seminales, and the fore end of the ejaculatory duct (_utriculi majores_
and _breviores_); another large conglobate gland opens separately to
the exterior. We shall now describe the structure of these parts in
more detail.[168]
[168] We propose to notice here the chief differences which we have
found between the figures of Brehm (_loc. cit._), which are the
fullest and best we have seen, and our own dissections.
Figs. 10, 11 (pp. 169–70). The ejaculatory duct and duct of the
conglobate gland are made to end in the penis (_infra_, p. 178).
Figs. 14, 15 (p. 173). These figures seem to us erroneous in many
respects, such as the median position of the penis and titillator.
Fig. 16 (p. 174). The pair of hooks marked _E_ are too small, and
there are additional plates at the base, which are not figured (see
our fig. 102). _F_ (of our fig.) is omitted.
The testes may be found in older larvæ or adults beneath the fifth
and sixth terga of the abdomen. They lie in the fat-body, from which
they are not very readily distinguished. Each testis consists of 30–40
rounded vesicles attached by short tubes to the vas deferens.[169] The
wall of the testis consists of a peritoneal layer and an epithelium,
which is folded inwards along transverse lines. The cells of the
epithelium give rise to spermatocysts,[170] which enclose sperm cells.
By division of the nuclei of the sperm cells spermatozoa are formed,
which have at first nucleated heads and long tails. Subsequently the
enlarged heads disappear. The spermatozoa move actively. In adult males
the testes undergo atrophy, but can with care be discovered in the
enveloping fat-body.
[169] In _Blatta germanica_ the testes are functional throughout
life. They consist of four lobes each. The vasa deferentia are much
shorter than in _P. orientalis_.
[170] The spermatocysts are peculiar to Insects and Amphibia. They
arise by division of the spermatospores, or modified epithelial
cells, and form hollow cysts, within which sperm cells (or
spermatoblasts) are developed by further division. The sperm cells
are usually placed radiately around the wall of the spermatocyst.
They escape by dehiscence, and are transformed into spermatozoa.
[Illustration: Fig. 99.--1. Male Organs, ventral view. _Ts_, testis;
_VD_, vas deferens; _DE_, ductus ejaculatorius; _U_, utriculi majores;
_u_, utriculi breviores. 2. Do., dorsal view, showing termination of
vasa deferentia. 3. Conglobate gland, and its duct. × 8.]
The vasa deferentia are about ·25 inch in length. They pass backwards
from the testes, then turn downwards on each side of the large
intestine, and finally curve upwards and forwards, entering the
vesiculæ seminales on their dorsal side. Each vas deferens divides
once or twice into branches, which immediately reunite; in the last
larval stage the termination of the passage dilates into a rounded,
transparent vesicle.
[Illustration: Fig. 100.--Male Organs, side view. _T^7_, seventh
tergum; _S^7_, seventh sternum; _Ts_, _DE_, as before. _A_, _B_, see
fig. 102. × 8.]
The vesiculæ seminales are simple, rounded lobes in the pupa
(fig. 101), but their appearance is greatly altered in the adult by the
development of two sets of utricles (modified accessory glands). The
longer utricles (_utriculi majores_) open separately into the sides
of the vesiculæ; nearer to the middle line are the shorter and more
numerous _utriculi breviores_, which open into the fore part of the
vesiculæ.
The utricles form the “mushroom-shaped gland” of Huxley, which was long
described as the testis. In the adult male the utricles are usually
distended with spermatozoa, and of a brilliant opaque white.
The ejaculatory duct is about ·15 inch long, and overlies the 6th-9th
sterna. It is wide in front, where it receives the paired outlets of
the vesiculæ seminales. Further back it narrows, and widens again near
to its outlet, which we find to be between the external chitinous
parts, and not into the penis, as described by Brehm. The duct
possesses a muscular wall for the forcible ejection of its contents,
and in accordance with its origin as a folding-in of the outer surface,
it is provided with a chitinous lining. In the adult the fore part of
the duct may be distended with spermatozoa.
[Illustration: Fig. 101.--Vesiculæ Seminales and Ductus Ejaculatorius
of Pupa. _VD_, vas deferens. × 28.]
The ejaculatory duct is originally double (p. 194), and its internal
cavity is still subdivided in the last larval stage or so-called “pupa.”
Upon the ventral surface of the ejaculatory duct lies an accessory
gland of unknown function; it is “composed of dichotomous, monilated
tubes, lined by a columnar epithelium, all bound together by a
common investment into a flattened, elongated mass.”[171] The duct
of this gland does not enter the penis, as described by Brehm, but
opens upon a double hook, which forms part of the external genital
armature (fig. 99, 3). It may be convenient to distinguish this as the
“conglobate gland.”[172]
[171] Huxley, Anat. Invert. Animals, p. 416.
[172] The term “accessory gland,” used by Huxley and others, is
already appropriated to glands which we believe to be represented
by the utricles of the Cockroach, and which have only a general
correspondence with the gland in question.
The external reproductive organs of the male Cockroach are concealed
within the 9th sternum. The so-called penis (fig. 102) is long,
slender, and dilated at the end. It is not perforated, and we do not
understand its use, though it probably conveys the semen.
[Illustration: Fig. 102.--External Male Organs, separated. The
lettering agrees with Brehm’s figures. _A_, titillator; _B_, penis;
_C-F_, hooks and plates. × 8.]
The “titillator” (Brunner von Wattenwyl) is a solid curved hook with
a hollow base. Besides these, are several odd-shaped, unsymmetrical
pieces (fig. 102, _C_, _D_, _E_, _F_), moved by special muscles. A pair
of styles (see figs. 32–3 and 103) project from the hinder edge of the
9th sternum. These paired and unpaired appendages are believed to open
the genital pouch of the female, but we do not understand their action
in detail.[173]
[173] Similar organs, forming a male genital armature, have been
described in various Insects. See Burmeister, Man. of Entomology,
p. 328 (Eng. Transl.); Siebold, Anat. of Invertebrates; Gosse
in Linn. Trans., Ser. 2, Vol. II. (1883); Burgess on Milk-weed
Butterfly, Ann. Mem. Bost. Soc. Nat. Hist.; &c.
Brehm observes that the male reproductive organs of the Cockroach are
most nearly paralleled by those of the Mantidæ. A free penis occurs in
all Orthoptera, except Acridiidæ and Phasmidæ.
The male organs of the House Cricket will be found much easier to
understand than those of the Cockroach. The testes are of irregular,
oval figure, the vasa deferentia very long, tortuous, and enlarged
towards the middle of their length. The vesiculæ seminales bear many
utriculi majores et breviores. The penis is of simple form, and dilated
at the end. The titillator is broad, but produced into a slender prong,
which projects beyond the penis. A pair of subanal styles is found, but
the unpaired hooklets are wanting or very inconspicuous.
[Illustration: Fig. 103.--The Tenth Tergum reflected to show the
external male organs _in situ_. _T^{10}_, tenth tergum; _p_, podical
plates; _A-F_, as in fig. 102; _S_, sub-anal styles. × 8.]
Very little is known about the act of copulation among Cockroaches,
and the opportunities of observation are few. The following account is
given by Cornelius (_loc. cit._, p. 22):--
“The male and female Cockroaches associate in pairs, the females
being generally quiet. The male, on the contrary, bustles about
the female, runs round her, trailing his extended abdomen on the
ground, and now and then raises his wings. If the female moves
away, the male stops the road. At last, when the female has become
perfectly still, the male goes in front of her, brings the end
of his abdomen towards her, then moves backwards, and pushes his
whole length under the female. The operation is so rapid that it is
impossible to give an exact account of the circumstances. Then the
male creeps out from beneath the female, raises high both pairs of
wings, depresses them again, and goes off, while the female usually
remains quiet for some time.”