. Text book of zoology. Zoology. Class 4. Nemertinea. 155 already mentioned^ there are auditory vesicles in a few forms. In contrast to other Flatworms, the Nemertines possess a vascular system, usually consisting of three principal longitudinal trunks, two lateral, and one dorsal, which come into relation with one p /u- another anteriorly and pos- teriorly, and are besides con- nected by transverse vessels. The blood flows from behind forwards in the dorsal vessel, from before backwards in the lateral vessels; it is colourless or red. The Nemertines are almost always or separate Fig. lie. Dia
. Text book of zoology. Zoology. Class 4. Nemertinea. 155 already mentioned^ there are auditory vesicles in a few forms. In contrast to other Flatworms, the Nemertines possess a vascular system, usually consisting of three principal longitudinal trunks, two lateral, and one dorsal, which come into relation with one p /u- another anteriorly and pos- teriorly, and are besides con- nected by transverse vessels. The blood flows from behind forwards in the dorsal vessel, from before backwards in the lateral vessels; it is colourless or red. The Nemertines are almost always or separate Fig. lie. Diagrammatic transverse section sexes; the sexual organs are °^ ^ Nemertine. d Dorsal vessel, g gonad, , . , . , h skin, i gut, I lateral vesEel, Jm longitudinal much Simpler m structure than muscle, « lateral nerve cord, p proboscis, ps those of other Platyhelminths. proboscis sheath, r circular muscle. Many ovaries or testes are present, opening by one duct on the side of the body. There are no accessory and no copulatory organs. Some Nemertines undergo a metamorphosis, which is aberrant, in that the principal part of the larval body atrophies. The larva, which is sometimes of a peculiar form (Fig. 117) is free- Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Boas, J. E. V. (Johan Erik Vesti), 1855-1935; Boas, J. E. V. (Johan Erik Vesti), 1855-1935. Lehrbuch der Zoologie. London, Sampson Low, Marston
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
