. Principles of modern biology. Biology. B SOMITES SPINAL NERVE SOMITES DIGESTIVE TRACT COELOM GENITAL RIDGE. GILL CLEFTS HEART Fig. 15-11. Some generalized stages in the development of a primitive verte- brate. Stages A to E are cross sections cut from the mid-body region; whereas F is a longitudinal section. nerves of the bod) represent outgrowths from the neural tube. Each nerve consists of a bundle of fibers that originate from nerve cells as soon as these begin to differen- tiate in the developing brain and spinal cord. The flexible unsegmented notochord is a skeletal rod that is found in
. Principles of modern biology. Biology. B SOMITES SPINAL NERVE SOMITES DIGESTIVE TRACT COELOM GENITAL RIDGE. GILL CLEFTS HEART Fig. 15-11. Some generalized stages in the development of a primitive verte- brate. Stages A to E are cross sections cut from the mid-body region; whereas F is a longitudinal section. nerves of the bod) represent outgrowths from the neural tube. Each nerve consists of a bundle of fibers that originate from nerve cells as soon as these begin to differen- tiate in the developing brain and spinal cord. The flexible unsegmented notochord is a skeletal rod that is found in all vertebrate embryos, extending lengthwise through the embryo—between the neural tube and the archenteron (Fig. 15-11 D,F). In vertebrates, however, the notochord is a short-lived, ves- tigial structure. In most cases it is totally replaced by the segmented vertebral column; but among primitive vertebrates (for exam- ple, lampreys, sharks, and frogs), remnants of the notochord can be found between the vertebrae, even in the adult 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 Marsland, Douglas, 1899-. New York, Holt, Rinehart and Winston
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