. Elementary text-book of zoology [electronic resource]. Zoology. 292 CHORD AT A, ventral vessel between the heart and the system, with the main sub-intestinal vein. A reversible heart such as this also occurs in some allies of Bala?wglossiis. Oc-sai v/essel Pharynx -^pnfrdl vessel. The main nerve-ganglion or brain lies dorsally between the mouth and atriopore, just under the ectoderm, and gives Nervous branches to the muscles. A main nerve- trunk runs back dorsally to the stomach. Under the brain lies a sub-7ieural gland, which communicates by a duct with the front part of the pharynx just in
. Elementary text-book of zoology [electronic resource]. Zoology. 292 CHORD AT A, ventral vessel between the heart and the system, with the main sub-intestinal vein. A reversible heart such as this also occurs in some allies of Bala?wglossiis. Oc-sai v/essel Pharynx -^pnfrdl vessel. The main nerve-ganglion or brain lies dorsally between the mouth and atriopore, just under the ectoderm, and gives Nervous branches to the muscles. A main nerve- trunk runs back dorsally to the stomach. Under the brain lies a sub-7ieural gland, which communicates by a duct with the front part of the pharynx just inside the ring of tentacles. It may possibly be an excretory organ. No special sense-organs are recognisable though the papillae around the mouth apparently function for testing the quality of the incurrent water. Excretory products are said to accumulate in solid masses in parts of the body, and to be extruded xcre y. death of the individual. No definite excretory organs have been described. Ascidia is hermaphrodite. 'I he testes and ovaries are simple paired sacs lying over the stomach and leading by separate ducts into the atrium. 'I he main interest attaching to Ascidia is involved in its development. If the anatomical account has been carefully Develo ment followed, it will have been noticed that Ascidia differs from nearly all the preceding types in having the nervous system co^ifified to the dorsal region of the body, in possessing numerous paired slits in the wall of the pharynx, and in the presence of a ventral heart, which is (in- termittently) respiratory, involving a backward current in the dorsal vessel and a forward in the ventral. These are all characters in which the Tunicata resemble the other members of the important phylum Chordata. In addition, in the structure of the pharynx, the method of feeding and the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1901
