. Text book of zoology. Zoology. Class 1. Leptoccu'dii. 355 posteriorly. Above this lies the central nervous systenija long cord-like organ without specialised brain; its central canal communicates with the exterior in front. There is an unpaired eye in the form of a pigmented spot in the anterior part of the. Fig. 293. Diagrammatic longitudinal section of Amphioxus. a anus, c notoohord, gill sac, m stomach, n central nervous system, p atrium, p' atriopore.—Orig. nervous system; paired eyes and auditory organs are absent. The musculature is arranged as in Fish, the muscle-fibres transversely s
. Text book of zoology. Zoology. Class 1. Leptoccu'dii. 355 posteriorly. Above this lies the central nervous systenija long cord-like organ without specialised brain; its central canal communicates with the exterior in front. There is an unpaired eye in the form of a pigmented spot in the anterior part of the. Fig. 293. Diagrammatic longitudinal section of Amphioxus. a anus, c notoohord, gill sac, m stomach, n central nervous system, p atrium, p' atriopore.—Orig. nervous system; paired eyes and auditory organs are absent. The musculature is arranged as in Fish, the muscle-fibres transversely striated. Below the notochord lies the alimentary canal, beginning at the anterior end of the animal with a mouth, surrounded by a number of projecting tentacles (cirrhi), this leads into a large pharynx, perforated by numerous transverse slits, and extending back through a large region 'of the body. Behind, the pharynx leads into the stomach, which is furnished with a large evagination, the liver; the intestine is short and straight and opens ventrally, not far from the hind end, so that the length of the tail is not great. The gill- clefts do not lead direct to the exterior, but open into an atrium surrounding the pharynx, and this again opens ventrally, anterior to the anus. In quite young- animals the branchial clefts open on the surface, but later a longitudinal fold develops above them on each side, and eventually grows round them, the two uniting on the ventral surface. The vascular system is remarkable for the absence of a specialised heart, but all the vessels are pulsatile. Below the pharynx is an unpaired vessel, which receives the venous blood from the body, and sends branches to the gill bars; from the latter the blood is collected into an aorta running below the notochord. A hepatic portal system is present as in other Vertebrata. Eed blood corpuscles are wanting. Numerous short ciliated tubes, arranged in a row on either side, serve for excretory organs; each tu
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
