from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A kidneylike organ, being either part of the most anterior pair of three pairs of organs in a vertebrate embryo, disappearing early in the embryonic development of higher vertebrates, but functioning as a kidney in some simple vertebrates, such as the lamprey.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A primitive kidney in the lamprey and similar animals, and in other vertebrate embryos
from the GNU version of the Collaborative International Dictionary of English
- n. The head kidney. See under head.
from The Century Dictionary and Cyclopedia
- n. Same as pronephron.
The anterior part of the kidney, called the pronephros, disappears in the later larval stages.
College, and now are arranged, numbered, and registered in order for use, there is evidence that in 1858 he, with his needles and eyeglass, had dissected and carefully figured the so-called pronephros of the
The pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but in their place is developed the genital gland in association with which the Wolffian duct remains as the duct of the male genital gland, the Müllerian as that of the female; some of the tubules of the metanephros form part of the permanent kidney.
A secondary glomerulus is formed ventral to each of these, and the complete group constitutes the pronephros.
The tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct.
These embryonic structures are on either side; the pronephros, the mesonephros, the metanephros, and the Wolffian and Müllerian ducts.
This continues to grow caudalward until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the Wolffian duct.
The pronephros undergoes rapid atrophy and disappears.
Another difference that appears later is that, while the tadpole has an efficient pronephros, the fowl, which has no larval (free imperfect) stages in its life history, has the merest indication of such
Figure 3, Sheet 17, is a generalized diagram of the uro-genital organs in the vertebrata; M.L. is the middle line of the body, G. is the genital organ, Pr. is the pronephros, or fore kidney,