. Text-book of zoology for junior students. Zoology. GENERAL CIIAUACTEIiS OF THE VEETEBKATA. 219 Leaving the brain and spinal conl out of siglit for a moment, we see tliat the lower or visceral tube of a Vertebrate animal contains tlie digestive canal (/;), the hiemal or blood-vasculai- system (c), and a system of nervous ganglia (/(). Now this is exactly what is con- tained within the visceral cavity of any Invertebrate animal ; and it follows from this that the " cerebro-spinal" nerve-system of the Vertehrata is a structui'e for which no pi-ccise ])arallel exists among Invertebrate
. Text-book of zoology for junior students. Zoology. GENERAL CIIAUACTEIiS OF THE VEETEBKATA. 219 Leaving the brain and spinal conl out of siglit for a moment, we see tliat the lower or visceral tube of a Vertebrate animal contains tlie digestive canal (/;), the hiemal or blood-vasculai- system (c), and a system of nervous ganglia (/(). Now this is exactly what is con- tained within the visceral cavity of any Invertebrate animal ; and it follows from this that the " cerebro-spinal" nerve-system of the Vertehrata is a structui'e for which no pi-ccise ])arallel exists among Invertebrates. Another peculiarity wliicli is present in all the Vertebrata is, that at an early period of life there is develojied in the liiwer wall of the tube which contains the cerebro-s|iinal axis a siugidar structure known as the " notochord," or "chorda doj'salis" (hg. 157, B, cli). This is a semi-gelatinous rod, tajiering at both ends, an<l extending along the floor of the cerebro-spinal tulie. In some cases the note- chord remains permanently in this condition, but in most cases it is replaced at maturity by the bony colunui or backbone, from which the Vertahrata derive their name. The general structure of the. 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, American Book Co
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