. Chordate anatomy. Chordata; Anatomy, Comparative. 8 CHORDATE ANATOMY phosis. The sexually-produced tailed larva bears certain striking resem- blances to the larva of Amphioxus. Some systematists recognize 1400 species. ClONA is a sessile tunicate, three or four inches in length, which is attached by tunicin stolons to its substratum. A tunicin test or tunic, which is secreted by the skin, encloses the entire animal as a sac. Beneath the test and loosely connected with it, except in the region of the two apertures of the body, lies the body-wall or mantle. This consists of an external simple
. Chordate anatomy. Chordata; Anatomy, Comparative. 8 CHORDATE ANATOMY phosis. The sexually-produced tailed larva bears certain striking resem- blances to the larva of Amphioxus. Some systematists recognize 1400 species. ClONA is a sessile tunicate, three or four inches in length, which is attached by tunicin stolons to its substratum. A tunicin test or tunic, which is secreted by the skin, encloses the entire animal as a sac. Beneath the test and loosely connected with it, except in the region of the two apertures of the body, lies the body-wall or mantle. This consists of an external simple epithelial ectoderm, and, beneath this, connective tissue containing a network of muscle fibers which are more abundant in the BRAIN CILIATED FVJNNEC MOUTH GILL SLITS â ATRIAL CAVITY/SPINAL CORD. \notochord intestine \ENDOsrYLE "^"^ B. METAMORPHOSIS. Fig. 9.âDiagrams of stages in the metamorphosis of a uruchordate larva. When the larva settles down and becomes fixed by its adhesive papillae, the tail is lost and the notochord disappears. Thus the chordate characters which are so evident in the larva are partly lost in the mature organism. (Redrawn from Korscheldt and Heider, after Seeliger.) region of the two apertures of the body, which they serve to close and open. Of the two external apertures, the more ventral is the inhalent or oral siphon and the other the exhalent or atrial siphon. The former leads directly to the mouth, which is surrounded by a circle of tentacles. The mouth leads into a greatly enlarged pharynx, which is perforated by numerous gill-slits or stigmata. The action of the cilia on the bars of these slits serves to maintain a current of water from the pharynx into the surrounding peribranchial or atrial cavity. Such relations resemble those of similar organs in Amphioxus. In the floor of the pharynx extends a longitudinal groove, the endostyle, which morphologists generally homologize with the thyroid gland of vertebrates. A somewhat similar gro
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Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
