. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE ANNELIDA. 239 in others the intestine bends upon itself and passes forward to open on the dorsal surface near the anterior end of the body (Fig. 109, A). Throughout the greater extent of the intestine there ruus along its ventral surface a ciliated groove which is no doubt homologous with the accessory in- testine of certain Polychseta (see p. 207). The nervous system partakes of the absence of distinct metamerism which characterizes the other parts. It consists of
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE ANNELIDA. 239 in others the intestine bends upon itself and passes forward to open on the dorsal surface near the anterior end of the body (Fig. 109, A). Throughout the greater extent of the intestine there ruus along its ventral surface a ciliated groove which is no doubt homologous with the accessory in- testine of certain Polychseta (see p. 207). The nervous system partakes of the absence of distinct metamerism which characterizes the other parts. It consists of a brain lying in the anterior portion of the body above the oesophagus and sending a com- missure downwards and backwards on each side to form the circum- oesophageal collar. These two com- missures unite to form a single nerve-cord (Fig. 109, li) extending the entire length of the body in the ventral median line, diflteriug from the ventral cord of the Chaetopoda in the absence of ganglia. Nerve- cells are scattered along the entire length of the cord and are not aggregated into special ganglia, though slight indications of such an aggregation are found in Priapu- lus. Nerves are given off at more. Fig. 109.—Stuuctuue of Si- punculus Oouldii (after an- drewr). A = nnus. Bs = blood vessel. , , . , . , rfR = dorsiil retmctormuscle. or less regular intervals on either J^^ ^ i„(estitie. side, a somewhat metaiueric ap- n = nerve-conl. pearance being thus produced, but ^ = nephridium. the corresponding nerves of op- Oe = ai,ox>\mgus. Ov = ovfti'v posite sides do not invariably arise ^^ ^ ^^.„j,,;, ,etractor muscle. from the cord opposite each other. One, two or three pairs of nephridia (Fig. 109, ne) are as a rule present and form conspicuous brown tubes, which com- municate by a funnel with the body-cavity at one extremity and with the exterior of the body at the other. They are. Please note that these images are extracted from scanned page images that may have been dig
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
