. Outlines of zoology. Zoology. 652 MAMMALIA. senses, its abandonment, except perhaps in human embryo- logy, is ahnost imperative.] The complex union of allan- tois with diplotrophoblast, Hubrecht calls the allan- toidean trophoblast. (6) But in the hedgehog, rabbit, and some other types, there is a mode of embryonic nutrition between that attained by the epiblastic trophoblast and that effected by the final placenta. The wall of the yolk sac, hypoblastic internally, meso- blastic externally, unites with the subzonal membrane, and becomes the seat of villous processes, which through the extern
. Outlines of zoology. Zoology. 652 MAMMALIA. senses, its abandonment, except perhaps in human embryo- logy, is ahnost imperative.] The complex union of allan- tois with diplotrophoblast, Hubrecht calls the allan- toidean trophoblast. (6) But in the hedgehog, rabbit, and some other types, there is a mode of embryonic nutrition between that attained by the epiblastic trophoblast and that effected by the final placenta. The wall of the yolk sac, hypoblastic internally, meso- blastic externally, unites with the subzonal membrane, and becomes the seat of villous processes, which through the external epiblast are connected with the uterine wall. Thus is formed what Hubrecht calls an omphaloidean trophoblast. Neither omphaloidean nor allantoic villi ever directly interlock with maternal tissue, but always through the agency of the external epiblastic trophoblast. (7) It is now time to turn for a little to the maternal tissue. Fig. 227.—Development of Fcetal Membranes. (After Hertwig.) Uppermost figure shows up-growth and down-growth of amnion folds" E.^ em- bryo; ^ amnion fold; «i., amnion proper; rt2., subzonal membrane; i^-., the gut ; _j'., umbilical vesicle or yolk sac. The dotted line represents mesoderm, the dark, hypoblast. The second figure shows origin of allantois, and the aninion folds have met. The third figure shows increase of allantois (al.); the dwindling yolk {y-s.')\ , amniotic cavity; s^, sub- zonal membrane. The fourth figine shows the embryo apart from its luem- branes; «;., mouth; a., anus. Note umbilical connection with yolk Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Thomson, J. Arthur (John Arthur), 1861-1933; Newbigin, Marion I. (Marion Isabel), 1869-1934; Smith, Preserved, 1880-1941. fmo. New York, D. Appleton & Co.
Size: 797px × 3137px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
