. Text-book of embryology. Embryology. IV PEONEPHEOS 237 lumen. The pronephric swelling extends backwards into the archi- nephric duct. No glomerulus develops but segmentally arranged branches of the dorsal aorta appear on the right side corresponding in number and degree of development with the pronephric tubules. These give rise either one of them (Eiickert, van Wijhe) or by fusion together (Eabl) to the root of the vitelline artery but are termed by Eabl pronephric arteries. The pronephros undergoes rapid degeneration and eventually nothing is left of it but the coelomic funnel of the Miill
. Text-book of embryology. Embryology. IV PEONEPHEOS 237 lumen. The pronephric swelling extends backwards into the archi- nephric duct. No glomerulus develops but segmentally arranged branches of the dorsal aorta appear on the right side corresponding in number and degree of development with the pronephric tubules. These give rise either one of them (Eiickert, van Wijhe) or by fusion together (Eabl) to the root of the vitelline artery but are termed by Eabl pronephric arteries. The pronephros undergoes rapid degeneration and eventually nothing is left of it but the coelomic funnel of the Miillerian duct (see below). Saueopsida.—In the fowl pronephric tubule rudiments develop to the number of about 12, in the form of solid outgrowths of the somatic mesoderm at the level of the nephro- tomes although, except in the case of the most anterior, the mesoderm is not yet segmented at this level at the time when the rudiments appear. In at least some cases segmental dilatations of the otherwise split-like coelome occur op- posite the tubule rudiments and are no doubt to be interpreted as the nephro- coeles of the corresponding tubules. The first tubule rudiment makes its appearance in embryos with 8 or 9 segments, its position showing consider- able variation (usually segment 4, 5 or 6). The successive tubules appear in rapid succession—almost synchronously. At about the 19-segment stage the myotomes become separated from the nephrotomes, the latter remaining continuity with the lateral mesodi and their cavities (nephrocoeles) with the splanchnocoele. About the same stage the backwardly projecting tip of each tubule rudiment undergoes fusion with its successor in the series and thus gives rise to a continuous longitudinal rod-like structure — the rudiment of the archinephric duct (Felix, 1904). The archinephric duct in its anterior portion thus would appear to develop in a manner essentially the same as that found in the Gymnophiona and so many other of the lower verte
Size: 1283px × 1949px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
