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The prevailing view now is that the processes of filtration and secretion are both carried on by the kidneys,—that the capillary clusters in the Malpighian bodies serve as delicate filters for the separation of water and salts, while the secreting cells of the tubules separate substances by the process of secretion.
The first forms the clusters in the Malpighian capsules and receives the blood directly from the smallest arteries. From the last set of capillaries the blood is passed into veins which leave the kidneys where the artery branches enter, uniting there to form the main renal veins. *Work of the Kidneys.*—Why should the blood pass through two systems of capillaries in the kidneys?
Bright’s disease of the kidneys affects the uriniferous tubes and interferes with their work. What impurity is then left in the blood? Trace water and salts from the Malpighian capsules to the bladder, naming parts through which they pass. Trace carbon dioxide from the cells to the outside atmosphere.
Branch from renal vein. 3. Small artery branches, one of which enters a Malpighian capsule . 6. Small vein leaving the capsule and branching into the capillaries which surround the uriniferous tubules. 4. Small veins which receive blood from the second set of capillaries. 8. Tubule showing lining of secreting cells.
They found in its mouth the buccal pieces of the Neuroptera, and, under the carapax, five pairs of branchial tufts attached to the segments that are invisible outwardly. Inside the animal were found tracheae, the digestic tube of an insect, and malpighian canals. Finally, in June, 1880, Mr. Vayssiere was enabled to establish the fact definitely that the insect belonged among the Ephemerids.
This is because the separation of waste is done in part by the Malpighian capsules and in part by the uriniferous tubules. Water and salts are removed chiefly at the capsules, while the remaining solid constituents of the urine pass through the secreting cells that line the tubules.
At its posterior end are given off five long slender processes, the Malpighian tubules which are organs of excretion, acting like the kidneys of higher animals. The hindgut is that portion of the intestine from the stomach to the end of the body. Anopheles at left. Lying under the alimentary canal in the forward part of the thorax are the salivary glands.
These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules. Vertical Section of the Kidney. Function of the Kidneys. The Malpighian capsules are really the beginning of the tubules, for here the work of excretion begins.
Of the two parts that compose the comb-shaped primitive kidney the longitudinal channel, or nephroduct, is always the first to appear; afterwards the transverse "canals," the excreting nephridia, are formed in the mesoderm; and after this again the Malpighian capsules with their arterial coils are associated with these as coelous outgrowths.
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