. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. tissue is defined as a group of cells having similar structure and function and ar- ranged in a compact, organized array. Thus, we talk of connective tissue or bone tissue or epidermal tissue. The revolu- tionary transformation of multicellular organisms from quasi-amorphous con- glomerates of cells into structures with well-defined tissues was a significant step, for it enabled these tissues subse- quently to combine into organs and or- gan systems and thus permitted the leve
. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. tissue is defined as a group of cells having similar structure and function and ar- ranged in a compact, organized array. Thus, we talk of connective tissue or bone tissue or epidermal tissue. The revolu- tionary transformation of multicellular organisms from quasi-amorphous con- glomerates of cells into structures with well-defined tissues was a significant step, for it enabled these tissues subse- quently to combine into organs and or- gan systems and thus permitted the levels of complexity that higher animals have since attained. The most primitive group of organ- isms still extant that displays a definite tissue organization is the Phylum Coelen- terata (or Cnidaria as it is now called). This is a group of fresh-water and marine animals that includes Hydra (a favorite laboratory animal in elementary biology) and its relations, the sea anemones that of O Primitive abound on rocky coasts, the corals, the jellyfish, and the awesome Portuguese Man of War, whose toxin has paralyzed The many unwary swimmers and led to death by drowning. A brief resume of the gen- CoelenterateS eral properties of these organisms illus- trates their primitive condition: 1. The body is composed of only two tissues, the outer epidermis and the inner gastrodermis. These arise early in the development of the coelenterate em- bryo. In contrast, the tissues of all higher animals stem originally from three em- bryonic cell layers. Within the two coe- lenterate tissue layers are a number of cell types, some of which appear in Fig. 18. 37 The Development Animal. 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 Sussman, Maurice. Englewood Cliffs, N. J. , Prentice-Hall
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