. The development of the frog's egg; an introduction to experimental embryology. Embryology. 144 DEYELOPMEXT OF THE FROG'S EGG [Cii. XITI same in the older and younger embryos, or greater in the older embryo as a result of cell-division. three gill-slits The first pairs of appear almost si- multaneously ; the first two, however, before the third. When the tadpole leaves its capsule, there are five pairs of gill-slits; the two new pairs have appeared succes- sively behind the third. A horizon- tal section through the larva (Fig. 41) shows to best ad- vantage the five clefts at this stag-e. '^ T
. The development of the frog's egg; an introduction to experimental embryology. Embryology. 144 DEYELOPMEXT OF THE FROG'S EGG [Cii. XITI same in the older and younger embryos, or greater in the older embryo as a result of cell-division. three gill-slits The first pairs of appear almost si- multaneously ; the first two, however, before the third. When the tadpole leaves its capsule, there are five pairs of gill-slits; the two new pairs have appeared succes- sively behind the third. A horizon- tal section through the larva (Fig. 41) shows to best ad- vantage the five clefts at this stag-e. '^ The gill-pouches form vertical par- titions radiating- outwards from the pharynx to the surface - ectoderm, Each pouch is formed of a double fold of endoderm, the two layers of which are in close contact with each other. The outer ends of all five pairs of gill-pouches reach the ectoderm and fuse with its inner or nervous layer, "i The most anterior pouch or cleft. Fig. 41. —AR. Archenteron. BRi, BR2, BR3. Brancliial arches. Hi, H\ m. Gill-clefts. HB. Hyoid cleft. HM. Hyomaiulibular cleft. HY. Hyoid arch. IN. Infundibulum. OF. Olfactory pit. OS. Optic stalk. P. Pronephros. S. Segmeutal duct. (After Marshall.) 1 Marshall ('93).. 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 Morgan, Thomas Hunt, 1866-1945. New York, The Macmillan company; [etc. , etc. ]
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectembryology, bookyear1
