. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 502 DEVELOPMENT OF PRIMITIVE BODY FORM GASTROCOEL NFURAL ECTODERM—Jl.^S:^ih''£ (NEURAL PLATE) NOTOCHORD MESODERM. Fig. 248. Sinking of neural plate and epidermal overgrowth of neural plate in Ainphi- oxus. (Slightly modified from Conklin, '32.) (A) Sagittal section of embryo comparable to that shown in fig. 247F. (B, C, D) Sections through embryo as shown by lines B, C, D, respectively, on (A). Observe that the neural plate begins to sink downward
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 502 DEVELOPMENT OF PRIMITIVE BODY FORM GASTROCOEL NFURAL ECTODERM—Jl.^S:^ih''£ (NEURAL PLATE) NOTOCHORD MESODERM. Fig. 248. Sinking of neural plate and epidermal overgrowth of neural plate in Ainphi- oxus. (Slightly modified from Conklin, '32.) (A) Sagittal section of embryo comparable to that shown in fig. 247F. (B, C, D) Sections through embryo as shown by lines B, C, D, respectively, on (A). Observe that the neural plate begins to sink downward from region of closed blastopore and proceeds forward from this point. b. Formation of the Mouth, Anus, and Other Specialized Structures of the Metenteron At the anterior end of the metenteron, a broad, dorsal outgrowth occurs which continues up on either side of the notochord and becomes divided into right and left dorsal diverticula (fig. 249B, H). The left diverticulum remains small and thick-walled and later fuses with an ectodermal invagination to form the pre-oral pit, described as a sense organ. The right diverticulum, however, increases greatly in size, becomes thin-walled, and gives origin to the so-called head cavity. The mouth develops at a time when the larva acquires about 16 to 18 pairs of mesodermal segments or somites (fig. 249D). It appears when the over- lying epidermis about halfway up on the left side of the body fuses with the entoderm, a fusion which occurs just posterior to the forming pre-oral pit (left diverticulum). (See black oval fig. 249D, and fig. 249F.) At the time that the mouth forms, the entoderm opposite the first pair of somites pushes ventrally and fuses with the ectoderm. This area of fusion finally perforates and forms the first gill slit. The gill slit, once formed, moves up on the right side of the body (fig. 249E). The entodermal area from which the first and later gill slits make their appearance is known as the branchial rudiment
Size: 2161px × 1156px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
