In the human fœtus this structure, called 'gubernaculum testis,' fig. 594, consists of a central axis of soft gelatinous substance rife with nucleate cells and surrounded by fibrous tissue, which soon exhibits the striped characteristic of voluntary muscle. Some of these fibres rise from the bottom of the scrotum, 10, and traverse the abdominal ring, 6, here diagrammatically indicated in CURLING'S excellent article CCXLII"; by 'Poupart's ligament,' 7, 7: a second series of fibres, 9, arise from Poupart's ligament,' and, with the pubic fibres, 8, seem in many Lissencephala to be an inverted part of the internal oblique and transversales muscles: the whole, inclosed by aveolar tissue, and connected by a fold of 594 595 3 Diagram of the gubernaculum and testicle previous to its descent. CCXLII". Diagram of the testicle immediately after its arrival in the scrotum. CCXLII". peritoneum to the psoas muscle, extends to the testis, 2. This 'gubernaculum' shrinking or contracting, or both, between the fifth and six months of human gestation, draws the testis from below the kidney, 1, to the abdominal ring, 6, where it rests to the end of the seventh month. During the eighth month it traverses the inguinal canal, and by the end of the ninth month has reached the scrotum, where it is commonly found at birth, with the remnant of the scrotal part of the gubernaculum, fig. 595, 2. The iliac, 4, and the pubic, 5, portions of the muscular tissue have now become the cremaster': the bag of peritoneum, 3, 3, carried out with the testis, 1, is converted, by obliteration of the neck, into tunica vaginalis testis.' In scrotal Mammalia, as a rule, it remains pervious, and it communicates widely with the abdomen in periodical testiconda. CHAPTER XXXIX. MAMMARY AND MARSUPIAL ORGANS. § 413. In Monotremata.—In a female Ornithorhynchus, shot in December, and of which the corpora lutea' indicated that she had recently brought forth young, the mammary glands formed an oblong flattened mass on each side of the ventral parietes of the abdomen. Each gland was composed of between one hundred and two hundred elongated subcylindrical lobes, fig. 596, converging to a small oval areola, fig. 597, in the abdominal integument, situated between three and four inches from the cloaca, and about one inch from the medial line. The lobes are rounded and enlarged at their free extremities, and become narrower to about one-third from the point of insertion, where they end in slender ducts, fig. 596, a. Almost all the lobes are situated at the outer side of the areola, and consequently converge toward the mesial line of the abdomen in fig. 596 they are exposed by reflecting outward the skin. Between the gland and the integument the panniculus carnosus is interposed, closely adhering to the latter, but connected with the gland by loose cellular membrane. This muscle is here a line in thickness, its fibres are longitudinal, and, separating, leave an elliptical space for the passage of the ducts of the gland to the areola. On the external surface of the skin, when the hair is removed, this areola can only be distinguished by the larger size of the orifices of the lacteal ducts, compared with those for the transmission of the hairs. The orifices of the ducts thus grouped together form an oval spot, five lines in the long and three in the short diameter. Neither in this nor any other of the many specimens in which I have dissected the mammary glands was the surface on which the ducts terminated raised in the slightest degree beyond the level of the surrounding integument. In a full-grown female, killed in August, in which two enlarged ovisacs indicated the preparation of ova for impregnation, the mammary gland was reduced to the size given in fig. 598: diverging tracts of cellular sheaths with fat indicated a previous seasonal enlargement. Mercury injected into the substance of a lobe diffused itself 596 in minute globules through the parenchyma, and at a distance of an inch it entered a central duct, down which it freely ran to the areola, where it escaped externally from one of the minute orifices just described. This process was repeated on most of the lobes with similar results: the greater part of them terminated by a single duct Mammary gland. Ornithorhynchus; nat. size. LXXXI. Mammary areola, Ornithorhynchus; nat. size. LXXVI. opening exteriorly and distinct from the rest, but in a few instances the ducts of two contiguous lobules united into one, and in these cases the mercury returned by the anastomosing duct and penetrated the substance of the other lobe as freely as that into which. the pipe had been inserted. Some of the lobes injected by the reflux of the mercury through the duct, and of which it was more certain that the glandular structure and not the cellular membrane was filled, were dried, and various sections were submitted to microscopical examination. At the greater extremity they are minutely cellular, the cells communicating with ducts elongating as the lobule grows narrower, dilating, and terminating in a larger central canal, or receptacle, from which the excretory duct is continued. On making a section of the corium through the middle of the areola the ducts are seen to converge to the external surface, but there is no inverted or concealed nipple at this part, as in the Kangaroo. Fig. 599 gives a magnified view of this section, with the section of one of the dried and injected lobules. On the first announcement, by MECKEL, of the existence of abdominal glands of the size and structure shown in fig. 596, it was objected, that they did not possess the characters of a true mammary gland, and that they resembled rather the clusters of elongated follicles situated on the flanks of Salamanders, and still more to the odoriferous scent-glands at the sides of the abdomen in Shrews, which are most active at the season of the rut.' I put this question to the test, first by showing the true structure of the mammary lobules, and next by comparing the relative size of the glands with the condition of the ovaria.2 The abdominal scent-glands are present in both sexes, and become largest in the male Shrews: but, in the Ornithorhynchus the glands are confined to the female, and vary in degree of development at different periods in individuals of equal size, attaining an enormous development after gestation and being small at the rutting season. The secretion being conveyed outwardly by means of numerous long and narrow ducts indicates its fluid nature, and is contrary to the mode in which odorous substances are excreted. The excretory orifices are by no means extended over so wide a space, in proportion, as in the Shrew, but are collected into one which accords with the size of the mouth of the young animal, and this spot is situated in a part of the body convenient for the transmission of a lacteal secretion from the mother to her offspring. Compared with an ordinary mammary gland, that of the Ornithorhynchus differs chiefly in the absence of the nipple, and, consequently, of the surrounding vascular structure necessary for its erection. But the remarkable modification of the mouth in the young Ornithorhynchus removes much of the difficulty which previously attached itself to the idea of the possibility of an animal with a beak obtaining its nutriment by suction. The width of the mouth in the smallest observed Ornithorhynchus, fig. 600, corresponds with the size of the mammary areola; and the broad tongue, extending to the apices of the broad, short, and soft jaws, fig. 601, with the fold of integument continued across the angle of the mouth, are all modifications which prepare us to admit such a co-adaptation of the mouth of the young to the mammary outlet of the parent as, with the combined actions of suction in the recipient, and compression of gland in the expellent, to effect this essentially Mammalian mode of nourish ment. The circumstances which first attract attention in these singular objects, fig. 600, are the absence of hair, the soft flexible condition of the mandibles, and the shortness of these parts in proportion to their breadth as compared with those of the adult. The integument with which the mandibles are covered is thinner than that which covers the rest of the body, and smoother, presenting |