The minute anatomy of the supra-renal cap sules of Fishes is very similar. In the Salmon Ecker found them consisting of separate lo bules, which are deposited in a loose areolar tissue perforated by vessels, and which, in ad dition, receive a special covering of this areo lar tissue. Each lobule is composed of a number of large gland-vesicles, from 5 to 11 100ths of a line in size, which are surrounded by blood-vessels. Their membrana propria is completely structureless. In their contents we again recognise the pulverulent molecules, separate fatty granules, and vesicular and gra nular nuclei of 2-1000ths of a line in size. The granular substance is rolled around these nuclei in the manner before described ; so that part of them come to notice as spheres with out walls, while part are real cells, surrounded by a membrane, and of 7 to 9.100ths of a line in measurement. It is not unfrequent to find two or three nuclei, instead of one, in their interior. We have remarked an exactly si milar condition in the supra-renal capsules of the young Pike ; there is the same fibrous coat, giving off processes which pass into the interior, and thus isolate the gland-vesicles, but the supra-renal organs are less divided into lobules than in the fish previously con templated. The contents of the gland-vesicles vary according to their size.
In the supra-renal capsules which are smallest of all, and measure under 9-100ths of a line, there are no gland-vesicles to be seen, but only nuclei : to these we shall im mediately return. But in supra-renal cap sules which are somewhat larger, the nuclei are partly included in cells.
By a yet further enlargement of these or gans, the gland-vesicles also appear : they contain fine molecules, fatty granules, and nuclei. These are vesicular, flat, of circular or irregular form, and vary in size from 22 to 30-10,000ths of a line. Each of these nuclei contains a single or double nucleolus. Not unfrequently forms appear which may be con nected with a division of the nucleus, where it appears cut through the middle, or even incompletely broken up into three parts.
Finally, the gland-vesicles also contain cells. By enlarging, these cells experience a gradual transition into new gland-vesicles, which are contained within the larger ones ; so that we may distinguish them into mother vesicles and endogenous daughter-vesicles, just as often happens in other cells, to wit, those of cartilage. The endogenous vesicles occur in the older ones in variable numbers. The smaller gland-cells contain only a single nucleus ; others possess two or three of them, which sometimes lie closely packed on each other. Finally, in other cells, three, four, five, and snore nuclei occur ; and in this manner, by an increase in the number of the enclosed nuclei, and at the same time a continual fur ther extension of the cell membrane, the cells experience a transition into glandular ve sicles.
These conditions, which were_first observed by Ecker, and which I can completely con firm from an examination of the same animal, will quite permit us to conclude as follows regarding the development of the glandular vesicles. En the smallest gland-vesicles a multiplication of nuclei takes place, most pro bably from those already present, by the me thod of fission. This multiplication extends
itself to free nuclei, as well as to those which are included in cells. In the latter case, the cell-membrane must be more and more ex tended by the formation of the nuclei; and in this manner the cells of a gland-vesicle them selves are changed into new endogenous ve sicles. By this process, the mother vesicle itself is considerably extended ; so that, finally, its membrane comes into contact with the sheath of the supra-renal capsule. Finally, after the membrane of the mother vesicle is destroyed new areolar tissue seems to be developed between the secondary vesicles. In this way the small supra-renal capsules of the Pike experience their growth.
In large old Pikes, the process of multipli cation and growth seems no longer to occur. In their supra-renal capsules, the fibrous foundation is more considerable in quantity, so that by its means the gland-vesicles are more separated from each other.
So also in the genus Cyprinus, where a pre cisely similar structure of the supra-renal cap sules may be observed, one lights upon con ditions of nuclei in the gland-vesicles which suffice to prove the transition of gland-cells into gland-vesicles. As to the problematical organs of the Myxine and Petromyzon, the glands which Muller discovered in the Myxi noid fishes consist of tufts of small elongated lobules, which are clothed with a kind of cylin. drical epithelium.* Concerning the glands in the Petrornyzon, Ecker only remarks, that the microscopic constituents do not afford any foundation for the view that they are supra renal capsules.
III. Development. — The supra-renal cap sules begin at a very early date of foetal life. In the human subject they appear simul taneously with the kidneys in the seventh week. The mode of their commencement is not yet understood with certainty. Never theless there is scarcely any doubt that the statement of Arnold, according to which the supra-renal capsules are formed by a projec tion of the Wolffian bodies, is erroneous. Most embryologists, as Valentin*, Bischoff and others, find that another method of begin ning obtains, namely, that these organs are developed from an independent blastema, which certainly lies very close to the Wolffian bodies, but has nothing at all to do with them. According to Meckel's observations, both supra-renal capsules constitute at first only a single mass ; and Valentin's researches on the embryo of the Dog and Sheep harmonise with this statement. But, nevertheless, this opinion may be founded on an error. Midler found that the supra-renal capsules of a large human foetus at the eighth week were plainly double, only they lay very closely together at their inferior part. Bischoff's extensive re searches on the embryo of Man and other Mammalia, confirm this statement of Miller, and explain the error of Valentin and Meckel. The embryonal form of the supra-renal capsules in man is distinguished from the later condition by its being composed of large lobes ; and thus, to a great extent, it resembles its permanent condition in some animals.