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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 ·4in. 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.

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.

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

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.

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.

Bythetelescoping of the 8th and 9th somites the sterna take the position shown in fig.96B, 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.

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

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

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.

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.

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.

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

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.

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

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.

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):—

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