. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. INTRODUCTION 559 UNICELLULAR GLAND. Fig. 264. Diagrams pertaining to the skin of bony fishes. (A and B after H. V. Wilson: Bull. U. S. Fish Commission, Vol. 9, 1889, reprint, 1891; C after Kingsley: Comp. Anat. of Vertebrates, 1912, P. Blakiston's Son & Co., Phila.; F from Reed; Am. Nat., 41.) (A) Section of ectoderm (primitive epidermis) of 39-hr. embryo of Serranus atrariiis. the sea bass. (B) Epidermis of sea-bass embryo of 59 hrs. (C) Skin
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. INTRODUCTION 559 UNICELLULAR GLAND. Fig. 264. Diagrams pertaining to the skin of bony fishes. (A and B after H. V. Wilson: Bull. U. S. Fish Commission, Vol. 9, 1889, reprint, 1891; C after Kingsley: Comp. Anat. of Vertebrates, 1912, P. Blakiston's Son & Co., Phila.; F from Reed; Am. Nat., 41.) (A) Section of ectoderm (primitive epidermis) of 39-hr. embryo of Serranus atrariiis. the sea bass. (B) Epidermis of sea-bass embryo of 59 hrs. (C) Skin of the lungfish, Protopterus. (D) Integument of teleost fish with special reference to scales. (E) Higher power of epidermal and dermal tissue overlying scale in D. (F) Poison gland along pectoral spine of Schilheodes gyriniis. primitive epidermal layer of the skin eventually is composed of two simple cellular layers, an out(.r protective periderm, and a lower, actively proliferat- ing stratum germinativum. It is to be observed further that the periderm in the recently hatched frog embryo possesses ciliated cells (fig. 267H, I). These cilia, as in Amphioxiis (fig. 249B), are used for locomotor purposes, and also function to bathe the surface with fresh currents of water. As such, they probably play a part in external respiration. The periderm forms a protective covering for the actively dividing and dif- ferentiating cells below. In the mammals, the periderm occasionally is called the epitrichium, as it eventually comes to rest upon the developing hair. In Amphioxm, there is no periderm, and the epidermal tube (epidermis) remains as a single layer of one cell in thickness (fig. 250E, F). 2) Origin of the Dermal or Mesenchymal Component. In Amphioxus, the thin lateral and ventro-lateral walls of the myotome give origin to the derma- tome which comes to lie beneath the epidermal wall. From the dermatome arises the dermis or connective-tissue layer of the skin (fig. 250E, F). The
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