. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 3 FIGURES 1-3. Neural tissues induced in the isolated ectoderm through exposure to am- monia solution. Fig. 1. A brain-like structure with a "nasal placode" on the right side. Fig. 2. A large explant showing two extensive brain-like structures with many lumina, accompanied by some placodes and mesenchyme. Fig. 3. An irregular brain-like vesicle accompanied by epidermal balls with frontal glands. X ca. 60. Eye-type. In only two cases eye-like tissue is developed in connection with the brain-type differentiation. One
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 3 FIGURES 1-3. Neural tissues induced in the isolated ectoderm through exposure to am- monia solution. Fig. 1. A brain-like structure with a "nasal placode" on the right side. Fig. 2. A large explant showing two extensive brain-like structures with many lumina, accompanied by some placodes and mesenchyme. Fig. 3. An irregular brain-like vesicle accompanied by epidermal balls with frontal glands. X ca. 60. Eye-type. In only two cases eye-like tissue is developed in connection with the brain-type differentiation. One of them is provided with a pigment layer, while the other is accompanied by a lentoid. Neural mass. A group of neuralized cells without definite morphological char- acterization. This occurs regularly when small explants are perfectly neuralized and no epidermis exists to cover the neural tissue. Seven such cases are recorded. Neural balls. This category also has no corresponding normal structure. It is probably heterogeneous, comprising some neural vesicles \vhich are too small to be called a brain, and some bodies of placodal nature often enclosing large pigment- vacuoles. Eleven neural balls are differentiated in eight explants. Nose-type. Of eighteen nasal placodes obtained, thirteen are closely applied to the brain and show a fairly normal condition (Fig. 1). Two others are differ- entiated without accompanying neural tissue. Mesenchyme and mclanophores. These elements are differentiated definitely only in one explant in close relation to the induced neural tissue. They cannot be distinguished from the normal ones. Frontal glands. Typically differentiated glands are found in nine explants. They often form irregular groups with epidermal cells and are attached to the neuralized cell-mass as a protuberance (Fig. 3). The size of the explants varied from X mm. to X mm. (expressed in the major and minor axes of the fixed explants, which are assumed. Please
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
