The contents of their gland-vesicles closely resemble those of the Mammalia. There are the same fine pulverulent molecules of a pro tein compound ; and fatty granules, which are usually in very large quantity, have a yel lowish colour, and give rise to the tint pos sessed by the whole organ. Not unfrequently larger yellow drops of fat are visible. Besides these, we come upon the granular nuclei pre viously mentioned, possessing a size of 22 to 31-10,000ths of a line. Some of these nuclei are also enveloped in a fine granular mass, and exhibit a transition to cells in the mode which we witnessed in the Mammalia. Not unfrequently the nuclei are completely buried in fatty granules, through which they are only visible as clear spots. In the golden Eagle Ecker remarked complete cells filled with fatty granules ; these were probably caused by the usually finely granular cells becoming gradually filled with fat. In many of the gland-vesicles, on the contrary, the fat is re markably diminished in its proportion to the finely granular substance ; and it has been conjectured by Ecker, and with great pro bability, that this difference in the amount of fat depends upon the different stages of deve lopment of the gland-vesicles. In a very young Pigeon I have found scarcely any fat molecules, a fact which has some connection with this statement.
The minute anatomy of the supra-renal capsules of the Reptilia is as yet insuffi ciently known.
In the supra-renal capsules of Lacerta agilis, Ecker was with some difficulty able to re cognise the same condition as that seen in the higher Vertebrata; but the presence of a membrana propria around the gland-vesicles was especially indistinct. He only remarked masses of a darkish substance. These masses consisted of fatty granules of the nuclei al ready described, and of granulated globules, which contained a nucleus, and possessed a size of 31 to 44-10,000ths of a line.
In the Adder, the obscurity of the contents uncommonly aggravates the difficulty of ex amining their lobulated supra-renal capsules ; , but in the fcetal Adder of three inches length, Ecker was able to verify the separate gland vesicles in the usual manner. Here also nuclei were seen; and, besides these, large pale gland-cells, which could not long resist the action of water. Other cells were com pletely buried in fatty masses, just as they were seen to be in the carnivorous Mammalia.
The arrangement of the vessels of the supra-renal capsules is peculiar in the Snakes, inasmuch as the greater part of the blood is not brought to the organ by means of ar teries, but by veins. In consequence of this, the supra-renal capsules have a kind of portal venous system, such as is possessed by the kidneys of Reptilia and the liver of Verte brata. The afferent supra-renal arise by two branches from the wall of the body, and from the plexus venosus of the vertebral j canal ; and after a tolerably long and isolated course they reach the supra-renal capsules.
On an average, the right supra-renal capsule receives two or three branches ; but the left, which is wont to be smaller, only one or two. The arterial blood is brought to the supra renal capsule by one or two vessels which are branches from the aorta.
Both kinds of vessels ramify in the sub stance of these organs, so as to form a fine capillary network. The efferent supra-renal veins arise from this network in the form of numerous small trunks. They pass from the right supra-renal capsule immediately into the vena cava posterior; but from that of the left side into the inferior cava, and also into the efferent renal vein.
In his examinations of the Testudo grmca, Ecker found certain bodies, which he regards as the supra-renal capsules of the Chelonian reptiles. By microscopic examination, they appear as yellow granules which are grouped together in heaps. Each of these is en closed in a membrana propria, and thus con stitutes a gland-vesicle. Their contents are altogether identical with those of the Batra chia, to which we shall next apply ourselves.
In the tailless Batrachia, the yellow lobules already described consist of groups of vesicles. Their form varies ; sometimes it is round, sometimes oval, sometimes elongated or irre gular. The vesicles are always closed, and it is only when they are grouped together that they appear at first sight like blind sacs. Fatty granules constitute the greater part of their contents ; but besides these, the fine granular substance is also present. Clear spots may also be seen glimmering from amidst the contents of the gland, and isolation shows these to be cells of 5 to 9-1000ths of a line in diameter, with finely granular contents and a nucleus. The application of water renders this more visible. Part of these cells are de void of the cell membrane, but others of them exhibit it very distinctly. Besides these, free nuclei are found ; these are sometimes vesicular and contain a nucleolus, sometimes they appear to be granulated. The nuclei which are included in cells are always of the latter kind.
From these microscopic characters of their contents exactly corresponding with those of the higher Vertebrata, the import of these organs as supra-renal capsules is placed be yond all doubt.
The same structure obtains in the tailed Batrachians, only the nuclei and cells are larger, while a part of the latter are com pletely enclosed in fat. Numerous branches of the afferent renal veins break up anew in the supra-renal capsules, in order to provide it with venous blood, a condition which re minds us of that seen in the Snakes.