File:Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus (1953) (20483644379).jpg

Title: Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus
Identifier: comparativeembry00nels (find matches)
Year: 1953 (1950s)
Authors: Nelsen, Olin E. (Olin Everett), b. 1898
Subjects: Vertebrates -- Embryology; Comparative embryology
Publisher: New York, Blakiston
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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414 GASTRULATION SECONDARY NEURALIZATION EPIDERMAL TRANSPLANT INTO NEURAL PLATE ^^sff^.
Text Appearing After Image:
NEURAL Plat INTO EPIDER LATE TRANSPLANT M A L AREA Fig. 196. Ectodermal potencies of the amphibian gastrula. (A and B from Spemann. '38, after Fischer; C and D from Spemann. '38, after Spemann, '18.) (A) Induction of a secondary neural plate in the axoloti gastrula by five per cent oleic acid, emulsified in agar-agar. (B) Induction of secondary neural plate by nucleic acid from calf thymus. (C) Formation of neural plate tissue from presumptive epidermal cells transplanted into neural plate region. (D) Reverse transplant, presumptive neural plate becomes epi- dermal tissue. (d) Still more lateral and extending ventraliy are the lateral plate and ventral mesoderm (figs. 191F-I; 198A-C; 221). The third or inner germ layer of entoderm is encased within the mesodermal or middle germ layer. The entodermal layer is an oval-shaped structure con- taining a small archenteric cavity filled with fluid. Its ventral portion is heavily laden with yolk substance. Also, the future trunk portion of the archenteric roof is incomplete, the narrow notochordal band forming a part of its mid- dorsal area (figs. 19IF; 194B; 219D). Within each of these germ layers are to be found restricted areas destined to be particular organs. Each layer may be regarded, therefore, as a general mosaic of organ-forming tendencies. 4) Position Occupied by the Pre-chordal Plate Material. Another feature of the late gastrula remains to be emphasized, namely, the pre-chordal plate composed of entodermal and mesodermal cells integrated with the anterior end of the notochord. During gastrulation the pre-chordal plate invaginates with the entoderm and comes to occupy the roof of the foregut, just anterior to the rod-like notochord (fig. 191D-F). In this position it lies below the anterior part of the neural plate area; it functions strongly in the induction and formation of the cephalic structures, including the brain as indicated above. Because of this inductive ability, it is regarded as a principal part of the head

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