Portions of the kidney taken from the ophidian reptile, as seen under the microscope, highly magnified. A one portion of the kidney, showing—1. The trunk of the artery passing to be distributed to—2. The diverging tubuli, forming the uriniferous ducts which terminate in—3. The common excretory duct called ureter.—B another portion of the same kidney, showing the extremely convoluted course of—4. The uriniferous ducts. 5. The smaller excretory ducts, or secreting canals, converging and uniting to form—6. The common excretory duct called the ureter.] 739. It is a striking confirmation of the correctness of this view of the structure of the glandular apparatus, that whenever in the ascending series a gland appears for the first time in any class, the elementary bodies are so large, and are disposed in so simple a mode, that a slight examination is sufficient to demonstrate their primitive form, and to render it manifest that they consist either of vesicles, follicles, cæca, or tubuli, more or less aggregated. This is seen in the obvious structure presented by the liver, the pancreas, the salivary glands, and the mammæ, in the simple animals in which these organs first appear. Thus the liver in animals low down in the scale is manifestly composed of simple clustering follicles: in the fish the pancreas is composed of simple branched follicles: in the bird, the salivary glands are composed of simple parallel tubuli; and in the cetacea the breasts are composed of simple branched tubuli. [Illustration: Fig. CXC. A lobule of a gland in the progress of development in the ovum of the bird, as seen under the microscope, showing the origin of the excretory ducts in the semipellucid gelatinous blastema, and the branching and foliated arrangement of the follicles in which the excretory ducts terminate.]