THE URINO-GENITAL SYSTEM.

By cutting through the meso-rectum the posterior caval vein is seen, as a large vessel, arising by numerous transverse branches from the ventral surfaces of the kidneys and testes (Fig. 214 Cv), lying in the median line between the kidneys; by drawing it to one side the dorsal aorta is brought into view (Fig. 214 Ao). The testes are placed on the ventral surface of the kidneys, and together with the fat-bodies conceal the anterior portions of these organs. The posterior portions of the kidneys are covered by peritoneum only, and may by seen without further dissection. The kidneys lie dorsal to the peritoneum, and have this membrane on their ventral surfaces only; their dorsal surfaces are in contact with the lumbo-sacral plexus.

The ureters extend from the anterior border of the eighth vertebra to the middle of the urostyle, where they terminate by two orifices in the dorsal wall of the cloaca (Fig. 184).

The testes are entirely surrounded by peritoneum, except a small part (Hilus) of the inner surface, where the vessels and ducts enter.

The urino-genital organs are arranged in the same manner in the two sexes; the ovaries corresponding in position with the testes (Fig. 214), that is, they are bilaterally symmetrical, and placed on the ventral surfaces of the kidneys.

The oviducts (Fig. 224 Ov) lie externally to the kidneys and ovaries, and course through the whole length of the trunk from the roots of the lungs to the cloaca. The size of the ovaries and oviducts varies very greatly according to the season of the year; at times, the kidneys may be entirely hidden by them.

I. THE URINARY ORGANS.

A. The kidneys.

a. General description. Each kidney (Fig. 215) is a reddish-brown, elongated organ, almost semilunar in shape; the inner border being straight and the outer convex. The organ is flattened from above downwards, and decreases in thickness towards either end. In animals of average size the kidney is about 16 mm. long, and from 6 to 7 mm. broad. The kidneys lie parallel to the vertebrae.

The outer border is smooth and even, except at its posterior third, where a slight depression for the ureter exists; the inner border has usually two or three well-marked notches, the hindermost of which is the deepest (Fig. 215). Each notch is continued outwards as a groove, traversing the whole breadth of the ventral surface and containing a branch of the renal portal vein. The ventral surface is, as a whole, slightly concave, grooved, and lobulated; the dorsal surface is smooth and slightly convex.

b. [Minute structure. The kidney is enclosed in a thin capsule of fibrous tissue (Fig. 220 Bg), which sends in fine trabeculae to support the glandular structures and the blood-vessels.]

(1) The blood-vessels of the kidney are the renal veins, the renal arteries, and the renal portal vein.

α. The renal portal vein (p. 247) courses along the outer border of the posterior part of the kidney, and then along the outer margin of the dorsal surface; in this course it gives off large branches, which course inwards and forwards and supply numerous lateral twigs. These anastomose to form a network of vessels on the dorsal surface of the organ, from which very numerous large branches course downwards and somewhat inwards to join corresponding branches of the renal veins (Fig. 216 I).

β. The renal veins (p. 247) form a coarse plexus on the ventral surface of the kidney, from this numerous large branches (Fig. 216 I) course upwards and outwards.

The venous system between the renal portal veins on the dorsal surface, and the renal veins on the ventral surface, are so large that they can scarcely be named capillaries (Hyrtl).

γ. The renal arteries (p. 233) are distributed to the ventral surface of the kidney; their mode of distribution varies in different parts of the organ. A simple arrangement is that shown in Fig. 216 I, where a branch traverses the breadth of the kidney and gives off branches to the Malpighian corpuscles; in one case (C) I have seen two twigs passing to the same corpuscle; as a rule, however, each Malpighian corpuscle receives only one twig. A more general arrangement is that the artery courses nearer the ventral surface and in a more winding course, several twigs are then given off close together, from the convex surface of one of the curves, and these course to their respective corpuscles.

In the Malpighian corpuscle the arterial twig forms a series of loops and then passes out to open abruptly into one of the branches of the neighbouring venous anastomosis (Hyrtl).

(2) [The Malpighian corpuscles and their capsules (Figs. 216 I, 218 III). The corpuscles lie nearer the ventral than the dorsal surface. They are rounded oval bodies, formed of loops of an arterial twig, held together by a small amount of connective-tissue. Each corpuscle is enclosed in a capsule, which it incompletely fills (Fig. 217)‍78.

The capsules are formed of connective-tissue and lined with a flattened epithelium (Fig. 218 III): according to Duncan the fibrous coat is arranged in two layers (III a). Towards the opening of the uriniferous tube the epithelium increases in thickness.

According to Hyrtl, the corpuscles are arranged in two layers, a more superficial one and a deeper one; and are of two sizes, the larger being as a rule the more superficial (ventral).]

(3) [The uriniferous tubes (Figs. 217 and 218). Each tube originates at a narrow opening on the dorsal surface of a Malpighian capsule. The tube gradually widens and is lined with a short rounded or cubical epithelium (Roth), (Fig. 218 III); each epithelial cell bearing a small number of extremely small cilia (Bowman, Kölliker, Duncan, and others). The cilia of the cells nearest the capsule are directed towards it (Heidenhain), those of the cells further away have an opposite direction (Spengel). This portion of the tube is known as the neck; it courses dorsalwards.

The second portion of the tube (Tubulus contortus), (Fig. 218 III, IX, and XII) has a very tortuous course in the dorsal part of the kidney, and then winds towards the ventral surface. This portion is lined with columnar epithelium, which has granular contents, and possesses large distinct nuclei. The cells of this part of the kidney are usually more or less coloured with a golden-yellow pigment. According to Tornier it bears short cilia (Fig. 218 XIV).

The third portion corresponds with the narrow limb of Henle’s loop; it is lined with ciliated epithelium (Fig. 218 VIII, b to c), similar to that in the neck of the tube.

The fourth portion (Fig. 218 VIII, c to d, and XIII) represents the wider limb of Henle’s loop. It has a winding course in the ventral part of the kidney, and then ascends dorsally to open into a collecting-tube. The fourth part of the tube is lined with a short, columnar epithelium (Fig. 218 VIII, c to d), which has a clear, cuticular, free border, large nucleus, and a peculiar arrangement of the protoplasm, which shows a rod-like structure (Fig. 218 XI).

The collecting-tubes course transversely near the dorsal surface of the kidney (Fig. 217), and the uriniferous tubes meet them at right-angles. They are lined with a short polygonal epithelium (Fig. 218 VII).

The lobules of the kidney. When treated with proper reagents the kidney shows a marked tendency to separate into lobules (Fig. 219 I).

The lymphatics of the kidney (Fig. 216 III‍79) form an irregular network of fine canals with elongated meshes. They run chiefly in the direction of the blood-vessels. The large vessels, which supply the kidney, are surrounded by large lymphatics.]

The nerves of the kidney (Fig. 219 II79). Little is known of these. Nerve-fibres have been traced alongside the larger blood-vessel through the greater part of the kidney.

B. The ureters.

a. General description. In the males the ureters are, at the same time, the seminiferous ducts. Each ureter commences on the dorsal surface of the kidney by bifurcating branches, which are continuous with the collecting-tubes of the kidney. In the anterior two-thirds of the kidney the ureter is wholly on the dorsal surface; at the junction of the middle and posterior thirds it winds round to the outer border of the kidney (Fig. 214 Ur), and there lies in a groove accompanied by the renal portal vein (Fig. 220 Ur and Va), the two organs being intimately attached to the kidney substance and enclosed by the fibrous capsule (Bg).

C. The bladder.

This portion of the ureter possesses a spindle-shaped enlargement, which represents the Receptaculum seminis. In Rana temporaria the Receptaculum seminis forms a large saccular dilatation.

In its further course the ureter runs backwards and slightly inwards, converging with its fellow of the opposite side; the ureters lie free in the abdominal cavity, and terminate by two openings placed side by side in a groove on the dorsal wall of the cloaca (Fig. 214 S, S¹).

In females the ureters are intimately attached to the dilated oviduct, immediately after leaving the kidney; they pursue a similar course to those of the males, but are attached to the oviduct in the whole of their course to the cloaca.

b. Minute structure. The ureter is a tube composed of connective-tissue and involuntary muscular fibre, and lined with a mucous membrane. The mucous membrane is thrown into longitudinal folds, and consists, in the larger tubes, of two or three layers of epithelium (Fig. 218 V), that on the free surface is columnar; the deeper cells being rounded or polygonal. The larger branches of the ureter are lined with columnar epithelium (Fig. 218 VI), with small intervening cells. In some parts of the branches the columnar epithelium bears short cilia.

No glands have been found in the ureter or Receptaculum seminis; in Rana temporaria, however, the Receptaculum seminis possesses large, branching mucous glands (Wiedersheim).

a. General description. The urinary bladder (Fig. 185 HB) is closely attached to the ventral wall of the cloaca and is easily distended from that organ. In relation to the animal it is of very large size; in consequence of its being contracted in the middle it has two lobes, which may be of unequal size. The organ is somewhat heart-shaped (Figs. 184 and 185), with the narrow neck attached to the cloaca, into which it opens by a smaller aperture on the ventral surface. The aperture is surrounded by a small fold of mucous membrane.

b. [Minute structure. The urinary bladder is bounded by a thin, transparent wall, lined internally with mucous membrane, and covered externally by peritoneum.

(1) The muscular coat is formed of a network of fine bands of unstriated muscular fibre (Fig. 221); it is supported and completed by a connective-tissue layer, rich in connective-tissue corpuscles and yellow elastic fibres.

(2) The peritoneal coat is a single layer of endothelial cells derived from the peritoneum and resting on a very thin layer of subperitoneal tissue.

(3) The mucous coat is formed of epithelium resting on a layer of loose, areolar tissue. The epithelium (Fig. 221 I, II, and IV) is arranged in three layers: the cells of the uppermost (II and IV, a) always present a flat or convex border to the cavity of the organ; seen from their free surfaces (I) they have polygonal outlines intermixed with round apertures belonging to goblet-cells, the remaining surfaces of these cells are serrated. The cells of the middle layer (II and IV, b) are polygonal in outline, they are not so tall as the cells of the layer above; all their borders are serrated. The cells of the deepest layer (II and IV, c) are more or less pointed above where they project between the cells of the second layer; their lowest surfaces are flattened towards the subepithelial tissue, and all their surfaces are serrated.

The cells of all three layers possess a cell-wall, and finely granular contents, and each cell has a large oval nucleus (List).

The goblet-cells (Fig. 221 I and IV, d) vary very much in shape; they are always more or less rounded in outline: they vary greatly in size (from 190 µ to 54 µ in length); some possess ‘feet’ or basal prolongations, in others these are absent. They usually open freely by rounded apertures on the surface of the mucous membrane, but are sometimes closed. The nucleus is placed towards the base of the cell and surrounded by a smaller or larger amount of protoplasm. These cells usually extend into the middle layer of the epithelium, and they probably constitute unicellular mucous glands (List).

(4) The blood-vessels of the urinary bladder (p. 235) are very numerous and run in very tortuous courses; they are accompanied by large lymphatics and by nerves.

(5) The nerves of the urinary bladder (p. 191) are of both medullated and non-medullated fibres, which course together towards their points of distribution; the non-medullated fibres are, however, much more frequent than the medullated fibres (Wolff).

The non-medullated nerve-fibres stand in close relation with the nerve-ganglia of the bladder. These ganglia may be unicellular, or composed of groups of nerve-cells; the cells vary considerably in shape, round, oval, triangular, and other forms being equally frequent in their occurrence; to some extent the form appears to depend upon the number and position of the processes of the cells. The diameter of the cells varies from 0.05 mm. to 0.1 mm.; the nucleus has a diameter of 0.025 mm., that of the nucleolus measures 0.005 mm. (Wolff).

The cells may be unipolar or multipolar; the former are however rare. The processes of these cells supply the muscle-fibres (Fig. 221 V, a), and other non-medullated processes connect the cells with the nerves (V, b (Wolff)).

The number of muscular fibres is far in excess of the number of the fibres of distribution of the ganglia; Wolff hence concludes that the nervous impulse may pass from one muscle-fibre to another.]

II. THE REPRODUCTIVE ORGANS.

A. The male reproductive organs are the testes and their ducts.

a. General description. The relations of the testes have already been given (p. 234); the organs vary much in shape and size in different individuals and with the different seasons; when greatest they are spherical, or of a rounded oval form, occasionally cone-shaped or pear-shaped. The surface of the testes is not smooth, but presents a series of convexities, each corresponding to a lobule of the gland. At the hilus on the inner border the vessels pass to and from the organ, and the Vasa efferentia leave the testis.

The number of Vasa efferentia (Fig. 222 I and II) is subject to considerable variation, not only in different animals, but on the two sides of the same animal. In some cases these ducts form a network (I), in other cases this is absent (II); usually the ducts bifurcate at acute angles, just before entering the kidney. Most of the tubes so formed open into the collecting-tube; a few, however, end blindly in the mesorchium (I, †). The course of the Vasa efferentia from the testis is first inwards, within the mesorchium; on reaching the kidney they curve dorsalwards between that organ and the corresponding testis: the ducts then travel in the ventral surface of the kidney towards its inner border, where they open into a longitudinal canal (Bidder), (Fig. 222 I, L). Just before their terminations each duct has an enlargement (I, C), the exact import of which is unknown (see also Fig. 218 XV).

The collecting-tubes open into the ureter at the hinder extremity of the kidney.

b. [Minute structure. The testis possesses a thin connective-tissue capsule underneath its peritoneal covering (Fig. 223 II, a); this sends in trabeculae (b) towards the centre of the organ, and so encloses the separate lobules. Each seminiferous tube arises from an elongated irregular sinus placed towards the middle of the organ; the tubes (c) are slightly convoluted in their course towards the periphery, near which they branch (Spengel). The tubes are from 0.16 mm. to 0.12 mm. in diameter (Kölliker), and are lined with two kinds of cells (Fig. 222 III); the cells (x) nearer the periphery are rounded and have large rounded nuclei, the diameters of which vary from 0.013 to 0.02 mm.; these again possess large and distinct nucleoli. The other cells (y) are of elongated, spindle-shaped form; and have oval nuclei, with an average length of 0.016 mm. and an average breadth of 0.005 mm. (Neumann).

The rounded cells lie in groups which vary in thickness and arrangement, and are often compressed so as to have polygonal outlines. The spindle cells are arranged so as to radiate from the lumen of the tube to the periphery, at an angle which varies from 45 to 90 degrees; these are the spermatoblasts.

The various changes which the spermatoblasts undergo in the formation of spermatozoa will easily be understood by reference to Fig. 223 I, a to k, where i and k represent the fully developed spermatozoa. These have three parts, head, middle part, and tail, the respective lengths of which in the two species are, according to Neumann, the following:‍—

At the hilus of the testis the rounded cells of the seminiferous tubes are gradually modified to form short cylindrical cells (0.01 mm. long and 0.006 mm. broad), the spindle cells being absent (Neumann). The Vasa efferentia are also lined with a similar columnar epithelium (Spengel).]

B. The female reproductive organs.

The position of these organs has already been given (p. 335).

I. The ovaries.

a. General description.

Each sac-like ovary (Fig. 224) is subdivided by thin-walled septa into numerous complete chambers, to the inner walls of which the ova are attached. The walls of adjacent sacs are intimately attached to each other, and the subdivision corresponds with the external lobulated appearance of the organ. According to Spengel the number of lobules is about fifteen (Rathke nine to thirteen, Brandt nine). Whether this segmentation of the ovary corresponds with the segmentation of the body has not been determined (Spengel). No part corresponding with Bidder’s organ has been found in Rana esculenta.

During the breeding season the ovaries undergo an extraordinary increase in size so as to occupy the greater part of the body-cavity and to displace the other viscera. The ovaries are entirely surrounded by peritoneum.

b. Minute structure. [The layer of peritoneum covering the ovary possesses cilia (Thiry), the ciliated cells being arranged in isolated patches (Schweigger-Seidel, Waldeyer) on the ventral surface of the organ, and on the mesovarium; these patches are sometimes united by very fine connecting lines of ciliated epithelium; the ciliated epithelium is always sharply marked off from that surrounding it (Kolessnikow). Under the peritoneum is a thin layer of connective-tissue, which is prolonged inwards to form the septa above-described. To these septa are attached the ova.

Between the connective-tissue layer and the peritoneum are isolated patches of germinal epithelium (Fig. 225 IV); these are easily distinguished, by the rounded outlines of their cells, from the surrounding epithelial cells (Waldeyer, Kolessnikow). These patches of germinal epithelium measure from 0.093–0.186 mm. in diameter; the germinal cells average 0.0139–0.0232 mm. in diameter (Kolessnikow). The patches are most numerous on the outer surface of the ovary, and particularly so near the mesovarium.

The follicles contained in the ovary have a connective-tissue coat developed in a manner similar to that of higher animals; the primordial ova which they contain have large nuclei (0.0325 mm.). The epithelium of the follicles has an average diameter of 0.0232–0.0325 mm. (Kolessnikow).

Schultze’s description of the ovaries (l. c.) varies considerably from that of Waldeyer and Kolessnikow. Briefly he describes the ovaries as a series of sacs separated by and lined externally and internally by endothelium; between these two layers are found the germinal epithelium and follicles: the structures being held together by an extremely minute quantity of connective-tissue.]

II. The oviducts.

a. General description. In young animals the oviducts are quite straight, thin-walled, and of small calibre. During the breeding season, however, they undergo an immense increase in size, and become much convoluted; in this state they are forced in between the other abdominal viscera, and usually cover the whole of the kidneys, and sometimes even part of the ovaries (Fig. 224 Ov).

The openings of the oviducts into the pleuro-peritoneal cavity (p. 304) are semilunar slits, directed inwards and lined with ciliated epithelium (p. 306).

Immediately behind this opening (Ostium abdominale) the oviduct is contracted, and is there narrower than in the rest of its length; beyond this it expands, and then retains an even size nearly to its hinder extremity, where it suddenly expands (Fig. 224 Ut). This dilatation gradually diminishes in size as it proceeds backwards towards the cloaca, into which each tube opens on a small papilla. The dilated portions of the tubes lie close together, but do not communicate with each other; the opening of the right tube is always slightly behind that of the left side (Fig. 224 P). From the papillae, into which the oviducts open, a fold of mucous membrane extends backwards on the dorsal surface of the cloaca to meet its fellow of the opposite side at an acute angle (Fig. 224 *). The orifices of the ureters are placed within these folds.

b. Minute structure.

(1) The tubular portion of the oviduct has three walls: a peritoneal covering with sub-peritoneal tissue (a); a glandular layer (b); and an epithelial lining (c). Of these the glandular layer forms by far the thickest layer, especially during the breeding season, when it is much increased in thickness. It consists of long cylindrical glands, often bifurcated at their blind, peritoneal ends. The epithelial cells, with which they are lined, have the power of absorbing more than a hundred times their own weight of water (Boettcher). This layer is absent at the anterior opening of the oviduct.

The cells have an average diameter of 0.012 mm., the lumen of the individual glands 0.1 mm. (in spirit-hardened specimens, Neumann). The cells contain small rounded bodies of very varying size, which may exist singly, grouped, or even arranged in rows; they swell on the addition of water. Each cell possesses, in addition, an oval, granular, distinct nucleus. When treated with Müller’s fluid many of the secretory cells have the appearances shown in Fig. 225 II, d, e, f; they each possess an opening (x), (Neumann).

According to Neumann the great power of absorbing water, which the oviducts possess, is due to the presence of these bodies, which he names ‘colloid granules.’ The mucous secretion of these glands passes into the oviduct and surrounds the eggs on their passage towards the cloaca: it is due to this secretion that the egg-spawn is so extremely slippery and difficult to handle.

The inner surface of the oviducts is lined with a ciliated, columnar epithelium (Fig. 225 I), containing numerous goblet-cells (I and II).

(2) The dilated portion of the oviduct has much thinner walls than the anterior, narrower portion; the glands cease abruptly at the junction of the two parts. The outer coat also contains unstriated muscular fibre; the inner surface is lined with ciliated epithelium similar to that of the anterior portion.

The lymphatics of the oviducts form a net with polygonal meshes on their outer surfaces; from this branches pass inwards in the spaces between adjacent glands to the inner surface, where a network with elongated meshes is formed (Langer).

C. [The Cloaca.

a. General description. The cloaca is a short tube lying beneath the urostyle; anteriorly it receives the openings of the ureters, rectum, and bladder; and in the female the openings of the oviducts, in addition: posteriorly it terminates at the anus.

b. Minute structure. The cloaca is lined internally with a mucous membrane resembling that of the rectum, e.g. a simple layer of columnar epithelium, which rests on a submucous, areolar layer.

The outer walls consist of a thick superficial, longitudinal muscular layer, and a deeper, ill-developed, transverse muscular layer.

c. Special muscles of the cloaca.

(1) The M. sphincter ani surrounds the end of the cloaca from the anus to the tip of the urostyle. It consists of striated muscle.

(2) The M. compressor cloacae arises from the tip of the urostyle, and is inserted into the hinder end of the rectum; it is also attached to the symphysis of the iliac bones; from this point a few fibres pass to the anus (Hoffmann).]

III. THE ADRENALS.

a. General description. The adrenals are small yellow bodies attached to the renal veins on the ventral surface of the kidney, towards its outer border.

b. [Minute structure. The superficial layer of the adrenals consists of solid, rounded, or elongated groups of polygonal cells, containing numerous fat-granules; these represent the cortical substance of the corresponding organs of higher animals. The medullary part is present only in small quantity; it consists of small groups of polygonal cells, placed between trabeculae of connective-tissue; both trabeculae and cell-groups are covered with an endothelium. The whole organ is surrounded by a connective-tissue capsule, which sends in trabeculae to support the parenchyma (Hoffmann).

No nerves have been traced into these organs (Eberth).]

IV. THE FAT-BODIES.

a. General description. The fat-bodies (Fig. 226) are bright yellow, lobulated bodies, placed in front of the testes and ovaries respectively. The greater portion of each organ lies parallel to the long axis of the body, and from its anterior, posterior, and external borders are given off finger-like processes; these may divide dichotomously either near the base or more peripherally. The external processes are much the longest, and in the male often conceal the greater part of the testis (Fig. 226 FK). The organs vary greatly in size with the season of the year.