. A text-book of animal physiology [microform] : with introductory chapters on general biology and a full treatment of reproduction, for students of human and comparative (veterinary) medicine and of general biology. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. immalian ovum jse invertebrate 3nt from an ex- , ammalian ovum jatures of devel- (embryo proper lint out that the ovum, inclosing REPRODUCTION. 71 the yelk, so that the original disk which lay like a watch-glass on the rest of the ovum, has grown into a sphere. That portion ijf this area
. A text-book of animal physiology [microform] : with introductory chapters on general biology and a full treatment of reproduction, for students of human and comparative (veterinary) medicine and of general biology. Physiology, Comparative; Veterinary physiology; Physiologie comparée; Physiologie vétérinaire. immalian ovum jse invertebrate 3nt from an ex- , ammalian ovum jatures of devel- (embryo proper lint out that the ovum, inclosing REPRODUCTION. 71 the yelk, so that the original disk which lay like a watch-glass on the rest of the ovum, has grown into a sphere. That portion ijf this area nearest the pellucid zone {area vasctdosa) develops. H- Fio. 75.—Dlagraminatic transverse sections through a hjrpothetical nuunmal oosperm (Had- don). A. The yelk of the prlmitiTe mammalian oOsperm is now lost. B. Later stage; the non-embrronic epiblast nas grown over the emiwyonic area to form the covering cells. ep, epiblast of embryo; ep', epiblast of yelk-sac; Ay, primitive hypoblast; y.«, yelk-sac, or blastodermic vesicle. blood-vessels that derive the food-supplies, which replenish the blood as it is exhausted, from the hypoblast of the area opaca. The first indications of future structural outlines in the embryo is the formation of the primitive streak, an opaque band in the long diameter of the pellu- cid area, opaque in consequence of cell accummulation in that re- gion. Very soon a groove {primi- tive groove) extends throughout this band, which gradually occu- pies a more central position. The relative thickness of the several parts and the arrangement of cells may be gathered from Fig. 76. These structures are only tempo- rary, and those that replace them will be described subsequently. We have thus far spoken of cells as being arranged into epi- blast, hypoblast, and mesoblast. The origin of the first two has been sufficiently indicated. The mesoblast forms the intermediate germinal layer, and is derived from the primitive hypoblast, which diflferentiates int
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Keywords: ., bookauthormillswes, bookcentury1800, bookdecade1880, bookyear1889
