. Chordate morphology. Morphology (Animals); Chordata. pyloric valve yolk sac {periblast enclosed part stippled) intestinal portal stomach spiral valve. bile duct pancreas and duct stomach spleen Figure 9-18. Two stages in the development of the digestive tract of Amio. A, early embryo in dorsal view; B, 22-mm embryo in dorsal view. part of the intestine. This gland varies much in size; it is small in the rays, larger in the sharks. This compound tu- bular gland appears to function in control of blood salts. The liver is bilobed; the lobes are joined anteriorly, ven- tral to the esophagus. The
. Chordate morphology. Morphology (Animals); Chordata. pyloric valve yolk sac {periblast enclosed part stippled) intestinal portal stomach spiral valve. bile duct pancreas and duct stomach spleen Figure 9-18. Two stages in the development of the digestive tract of Amio. A, early embryo in dorsal view; B, 22-mm embryo in dorsal view. part of the intestine. This gland varies much in size; it is small in the rays, larger in the sharks. This compound tu- bular gland appears to function in control of blood salts. The liver is bilobed; the lobes are joined anteriorly, ven- tral to the esophagus. The gall bladder is large and embed- ded in the right lobe near the ventral midline. The pan- creas is compact but irregularly shaped and contains islet tissue. It lies below the anterior end of the intestine and ex- tends from here to the left below the pyloris. The spleen lies dorsal to the posterior end of the body of the stomach and extends around, behind and below, or along the pyloric section of the stomach. The spleen may extend to the right to underlie the pancreas and pieces of the spleen may ex- tend forward to the dorsal mesentery of the esophagus. A dorsal mesentery is present for the stomach and the anterior part of the intestine, also for the rectal gland. There is no ventral mesentery. Lymphoid and fatty tissue, other than the large spleen, is not evident. EMBRYOLOGicvL DEVELOPMENT The entoderm is divided early into a syncytial periblast on the surface of the yolk and the cellular entoderm of the blastodisc (Figure 7-10). The embryo develops at the posterior margin of the blasto- disc but involves somewhat more complex movements than the actinopterygian. Concrescence brings the cellular materials of the epiblast toward the midline of the posterior margin of the blasto- disc, and this is accompanied by forward and lateral move- ments in the hypoblast. In the prechordal area the hypo- blast is not already vertically delaminated into entoderm and mesoderm As the embryo
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Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
