. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. Fig. 123.—A, Transverse section of the body of one of the higher Inmrtelraia; a Body-wall: b Alimentary canal; c Hsemat system ; n Nervous system. B, Trans- verse section of the body of a Vertebrate animal: a Body-wall; b Alimentary canal; c Haemal system; n Sympathetic system of nerves; «' Cerebro-spinal system of nerves; ch Notochord. gangliated nervous system. Now this is exactly what is con- tained in the visceral cavity of any of the higher Invertebrate animals ; and it foll


. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. Fig. 123.—A, Transverse section of the body of one of the higher Inmrtelraia; a Body-wall: b Alimentary canal; c Hsemat system ; n Nervous system. B, Trans- verse section of the body of a Vertebrate animal: a Body-wall; b Alimentary canal; c Haemal system; n Sympathetic system of nerves; «' Cerebro-spinal system of nerves; ch Notochord. gangliated nervous system. Now this is exactly what is con- tained in the visceral cavity of any of the higher Invertebrate animals ; and it follows from this, as, pointed out by Von Baer, that it is the sympathetic nervous system of Vertebrates which is truly comparable to, and homologous with, the nervous sys- tem of Invertebrates. The cerebro-spinal nervous centres tif the Vertebrata are to be regarded as something superadded, and not represented at all amongst the Invertebrata. The tube containing the cerebro-spinal centres is formed as follows :—At an early period in the development of the em- bryo of any Vertebrate animal, the portion of the ovum in which development is going on—the "germinal area"—be- comes elevated into two parallel ridges, one on each side of the middle line, enclosing between them a, long groove, which is known as the " primitive groove" (fig. 124, A, B). The ridges which bound the primitive groove are known as the " laminse. 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 Nicholson, Henry Alleyne, 1844-1899. New York : D. Appleton


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