. A manual of zoology. Zoology. 112 GENERAL PRINCIPLES OF ZOOLOGY Diffuse Nervous System.—The diffuse type is certainly the most primitive; it sliows the two elements, nerve libres and ganglion cells, distributed through the whole body, or, at least, through certain layers of it. The skin of the body, the ectoderm, is one of the fundamental elements in the nervous svstem, since it is related to the external world, and hence receives the sensory impressions, so important for the de\'elop- ment of nervous tissue. The corals and hydroid polyps are examples, c. Fig. 77.—Third abdominal gani^Iion o
. A manual of zoology. Zoology. 112 GENERAL PRINCIPLES OF ZOOLOGY Diffuse Nervous System.—The diffuse type is certainly the most primitive; it sliows the two elements, nerve libres and ganglion cells, distributed through the whole body, or, at least, through certain layers of it. The skin of the body, the ectoderm, is one of the fundamental elements in the nervous svstem, since it is related to the external world, and hence receives the sensory impressions, so important for the de\'elop- ment of nervous tissue. The corals and hydroid polyps are examples, c. Fig. 77.—Third abdominal gani^Iion of a crayfish (after Rctzius'). C. connective or longitudinal commissure; C;", ganglion cell layer; .i;', ganglion cells whose neuritcs cnler die conneeli\c; ,£;-, ganglion cell whose neurites enter the peripheral nerve; L, granules, (Leydig's dolled subslanee); A", peripheral nerve. since in them the ectoderm is permeated in all directions by a subepi- thelial spider-weblike network of nerve fibres and ganglion cells, which encroach even upon the entoderm (tig. i;;). Linear Nervous System.—From the diffuse type the other chief types can be derived through concentration, which is chiefly conditioned by the fact that there are a few points which arc most ad\antageousIv located for the reception of sensory stimuli, and hence for the development. 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
