Thus the kidney is developed, consisting at first of a number of separate lobules; this condition remaining throughout life in many of the lower animals, e.g., seals and whales, and traces of this

Fig. 497.-Diagram showing the relations of the female (the left-hand figure 2) and of the male (the right-hand figure ) reproductive organs to the general plan (the middle figure) of these organs in the higher vertebrata (including man). C1, cloaca; R, rectum; B, urinary bladder; U, ureter; K, kidney; Uh, urethra; G, genital gland, ovary, or testis; W, Wolffian body: Wd, Wolffian duct; M, Müllerian duct; Ps t, prostrate gland; Cp, Cowper's gland; C sp, corpus spongiosum; Cc, corpus cavernosum.

In the female.-V, vagina; Ut, uterus; Fp, Fallopian tube; Gt, Gaertner's duct; Pv, parovarium; A, anus; Cc, Cs p, clitoris.

In the male.-C sp, Cc, penis; Ut, uterus masculinis; V s, vesicula seminalis; V d, vas deferens. (Huxley.)

lobulation being visible in the human foetus at birth. In the adult all the lobules are fused into a compact solid organ.

The supra-renal capsules originate in a mass of mesoblast just above the kidneys; soon after their first appearance they are very much larger than the kidneys (see fig. 497), but by the more rapid growth of the latter this relation is soon reversed.

The first appearance of the generative gland has been already described for some time it is impossible to determine whether an ovary or testis will be developed from it; gradually however the special characters belonging to one of them appear, and in either

case the organ soon begins to assume a relatively lower position in the body; the ovaries being ultimately placed in the pelvis ; while towards the end of foetal existence the testicles descend into the scrotum, the testicle entering the internal inguinal ring in the seventh month of fœtal life, and completing its descent through the inguinal canal and external ring into the scrotum by the end of the eighth month. A pouch of peritoneum, the processus vaginalis, precedes it in its descent, and ultimately forms the tunica vaginalis or serous covering of the organ; the communication between the tunica vaginalis and the cavity of the peritoneum being closed only a short time before birth. In its descent, the testicle or ovary of course retains the blood-vessels, nerves, and lymphatics, which were supplied to it while in the lumbar region, and which are compelled to accompany it, so to speak, as it assumes a lower position in the body. Hence the explanation of the otherwise strange fact of the origin of these parts at so considerable a distance from the organ to which they are distributed.

Descent of the Testicles into the Scrotum.--The means by which the descent of the testicles into the scrotum is effected are not fully and exactly known. It was formerly believed that a membranous and partly muscular cord, called the gubernaculum testis, which extends while the testicle is yet high in the abdomen, from its lower part, through the abdominal wall (in the situation of the inguinal canal) to the front of the pubes and lower part of the scrotum, was the agent by the contraction of which the descent was effected. It is now generally thought, however, that such is not the case; and that the descent of the testicle and ovary is rather the result of a general process of development in these and neighbouring parts, the tendency of which is to produce this change in the relative position of these organs. In other words, the descent is not the result of a mere mechanical action, by which the organ is dragged down to a lower position, but rather one change out of many which attend the gradual development and re-arrangement of these organs. It may be repeated, however, that the details of the process by which the descent of the testicle into the scrotum is effected are not accurately known.

The homologue, in the female, of the gubernaculum testis is a structure called the round ligament of the uterus, which extends through the inguinal canal, from the outer and upper part of the uterus to the subcutaneous tissue in front of the symphysis pubis.

At a very early stage of foetal life, the Wolffian ducts, ureters, and Müllerian ducts, open into a receptacle formed by the lower end of the allantois, or rudimentary bladder; and as this communicates with the lower extremity of the intestine, there is for the time, a common receptacle or cloaca for all these parts, which opens to the exterior of the body through a part corresponding with the future anus, an arrangement which is permanent in Reptiles, Birds, and some of the lower Mammalia. In the human fœtus, however, the intestinal portion of the cloaca is cut off from

that which belongs to the urinary and generative organs; a separate passage or canal to the exterior of the body, belonging to these parts, being called the sinus urogenitalis. Subsequently, this canal is divided, by a process of division extending from before backwards or from above downwards, into a 'pars urinaria' and a 'pars genitalis.' The former, continuous with the urachus, is converted into the urinary bladder.

The Fallopian tubes, the uterus, and the vagina are developed from the Müllerian ducts

(fig. 498, m and fig. 501) whose first appearance has been already described. The two Müllerian ducts are united

below into a single cord, called the genital cord, and, from this are developed the vagina, as well as the cervix and the lower portion of the body of the uterus; while the ununited portion of the duct on each side forms the upper part of the uterus, and the Fallopian tube. In certain cases of arrested or abnormal

development, these portions of the Müllerian ducts may not become fused together at their lower extremities, and there is left a cleft or horned condition of the upper part of the uterus resembling a condition which is permanent in certain of the lower animals.

Urinary and generative organs of a human female embryo, measuring 34 inches in length. Fig. 499.-General view of these parts; 1, supra-renal capsules; 2, kidneys; 3, ovary; 4, Fallopian tube; 5, uterus; 6, intestine; 7, the bladder.

Fig. 500.-Bladder and Generative organs of the same embryo viewed from the side; a, the urinary bladder (at the upper part is a portion of the urachus); 2, urethra; 3, uterus (with two cornea); 4, vagina; 5, part as yet common to the vagina and urethra; 6, common orifice of the urinary and generative organs; 7, the clitoris. Fig. 501.-Internal generative organs of the same embryo; 1, the uterus; 2, the round ligaments; 3, the Fallopian tubes (formed by the Müllerian ducts); 4, the ovaries; 5, the remains of the Wolffian bodies.

Fig. 502.-External generative organs of the same embryo; 1, the labia majora; 2, the nymphæ; 3, clitoris; 4, anus. (Müller.)

In the male, the Müllerian ducts have no special function, and are but slightly developed. The hydatid of Morgagni is the remnant of the upper part of the Müllerian duct. The small prostatic pouch, uterus masculinus, or sinus pocularis, forms the atrophied remnant of the distal end of the genital cord, and is, of

course, therefore, the homologue, in the male, of the vagina and uterus in the female.

sexes.

The external parts of generation are at first the same in both The opening of the genito-urinary apparatus is, in both sexes, bounded by two folds of skin, whilst in front of it there is formed a penis-like body surmounted by a glans, and cleft or furrowed along its under surface. The borders of the furrows diverge posteriorly, running at the sides of the genito-urinary orifice internally to the cutaneous folds just mentioned (see figs. 499-502). In the female, this body becoming retracted, forms the clitoris, and the margins of the furrow on its under surface are converted into the nymphæ, or labia minora, the labia majora pudendæ being constituted by the great cutaneous folds. In the male fœtus, the margins of the furrow at the under surface of the penis unite at about the fourteenth week, and form that part of the urethra which is included in the penis. The large cutaneous folds form the scrotum, and later (in the eighth month of development), receive the testicles, which descend into them from the abdominal cavity. Sometimes the urethra is not closed, and the deformity called hypospadias then results. The appearance of hermaphroditism may, in these cases, be increased by the retention of the testes within the abdomen.

CHAPTER XXIV.*

ON THE RELATION OF LIFE TO OTHER FORCES.

AN enumeration of theories concerning the nature of life would be beside the purpose of the present chapter. They are interesting as marks of the way in which various minds have been influenced by the mystery which has always hung about vitality; their destruction is but another warning that any theory we can

This chapter is a reprint, with some verbal alterations, of an essay contributed to St. Bartholomew's Hospital Reports, 1867, 1869, by W. Morrant Baker.