. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 558 INTEGUMENTARY SYSTEM during gastrulation and, in the post-gastrular period, is tubulated into the elongated, cylinder-like structure. The primitive epidermal tube thus forms the initial skin or outer protective investment of the developing body. The wall of the primitive epidermal tube at first may be composed of a single layer of cells of one cell in thickness, as in the shark, chick, pig, opossum, or human (figs. 263A; 269A; 272A). However,
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 558 INTEGUMENTARY SYSTEM during gastrulation and, in the post-gastrular period, is tubulated into the elongated, cylinder-like structure. The primitive epidermal tube thus forms the initial skin or outer protective investment of the developing body. The wall of the primitive epidermal tube at first may be composed of a single layer of cells of one cell in thickness, as in the shark, chick, pig, opossum, or human (figs. 263A; 269A; 272A). However, in teleost fishes and amphibia, the primitive epidermal tube is composed of two layers of cells. For example, in the sea bass, the wall of the primitive epidermal tube is composed of two layers, the outer layer being thin and made up of much-flattened cells and the lower layer being two cells in thickness (fig. 264A, B). In the anurans and urodeles, the wall of the primitive epidermal tube is composed of two layers, each of one cell in thickness (fig. 267A, D). The lower layer in the frog, salamander, anjd teleost often is referred to as the inner ectodermal or nervous layer. It is the germinative layer and thus forms the inner or lower portion of the stratum germinativum of the later epidermis (fig. 267A, D). The outer layer is densely pigmented and forms the periderm. In the embryo of the shark, chick, and mammal, the single-layered condition of the primitive epidermal tube soon becomes transformed into a double- layered condition, the outer layer or periderm being composed of much- flattened cells (figs. 263B; 269B; 272B). In all vertebrates, therefore, the MESENCHyME-4 ?'«>^i.,-^_^-4 W^:^. ^-^ ?^^ ENAMEL DENTINE ODONTOBLASTS DENTINE ORGAN). EP,OERM,sf ^E«'OERM^,^;^;^^p;«lgc%^ I STRATUM --e32fi9§55^j3;^S^- v.^Il'^^r^r^ LGtKMINATIVUM />' ^ '.% 'S^^.'-^V-" ,? Jg^^ .v^ iS^'cTi^^' DERMIS PIGMENT CELL^^^^^"^-*'"''^'--'""" ENAMEL DENTINE EPI
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Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
