from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. pronephric
from the GNU version of the Collaborative International Dictionary of English
- adj. Pronephric.
from The Century Dictionary and Cyclopedia
- Existing or acting instead of or prior to the definite formation of a kidney; of or pertaining to the segmental organ, or primitive kidney.
But in the Amniotes these primitive kidneys cease to act at an early stage of embryonic life, and their function is taken up by the permanent or secondary kidneys, which develop from the terminal section of the prorenal ducts.
The prorenal canals lie in the middle of the line of the head, outwards from the uppermost section of the gill-arches, and have important relations to the branchial vessels
The prorenal duct of the latter (Figure 2.218 C) corresponds to the branchial cavity or atrium of the former (Figure 2.217 C).
On the left a gill-rod has been struck, and on the right a gill-cleft; consequently on the left we see the whole of a prorenal canal (x), on the right only the section of its fore-leg.
At the side of the gut are two serpentine prorenal canals (water-vessels or pronephridia, nc), which open on the ventral side (nm).
A ectoderm (horny-plate), Mc medullary tube, ch chorda, C entoderm (gut-gland layer), Pv primitive segment (episomite), Wd prorenal duct, pp coeloma (secondary body-cavity).
For this reason, and in their whole arrangement, the primitive kidneys of the Amphioxus show clearly that they are equivalent to the prorenal canals of the Craniotes (Figure 2.218 B).
The dotted lines on the right indicate the later opening of the primitive kidney canals (A) into the prorenal duct (C).
Transverse section of a human embryo of fourteen days. mr medullary tube, ch chorda. vu umbilical vein, mt myotome, mp middle plate, ug prorenal duct, lh body-cavity, e ectoderm, bh ventral skin, hf skin-fibre layer, df gut-fibre layer.
The prorenal duct is visible in this gap even at the time of the severance of the medullary tube from the horn-plate.
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