. Text book of zoology. Zoology. Fig. Fig. 134. Diagram of the reproductive apparatus of an Earth-worm ; the animal is dissected from the mid-dorsal line and spread out. 8—14, 8th to 14th bristle-hearing seg- ments. 0 ovary, od oviduct, sb vesicula seminalis, sg spermatheca, t testis, vd vas deferens, vd' its outer end, ce receptaculum ovorum. The transverse hnes represent the septa.— Fig. 135. Larva of Nereis, a anus, m mouth, o eye.—After Gotte. Asexual reproduction occurs in not a few members of both groups. In some cases tbere is a simple transverse fission; the animal divides
. Text book of zoology. Zoology. Fig. Fig. 134. Diagram of the reproductive apparatus of an Earth-worm ; the animal is dissected from the mid-dorsal line and spread out. 8—14, 8th to 14th bristle-hearing seg- ments. 0 ovary, od oviduct, sb vesicula seminalis, sg spermatheca, t testis, vd vas deferens, vd' its outer end, ce receptaculum ovorum. The transverse hnes represent the septa.— Fig. 135. Larva of Nereis, a anus, m mouth, o eye.—After Gotte. Asexual reproduction occurs in not a few members of both groups. In some cases tbere is a simple transverse fission; the animal divides into two nearly equal parts, the posterior of which forms a new mouth, prostomium, etc., before the separation; whilst the anterior produces a new hind end. In other cases budding- takes place; the hindmost segment (or a number of posterior- segments) elongates and develops into a new individual, which then separates from the parent. Sometimes before separation, the latter begins to produce from its new posterior end, a second new individual in front of the first formed : the process may be repeated, so that a chain arises, consisting of a parent and several buds, of which the hindmost is the oldest and longest, and that nearest the parent is the youngest (Fig. 136). It will, however, easily be seen that a sharp line cannot be drawn between the fission and budding of Chsetopods; in both cases certain of the posterior segments of the original individual become a new individual; in the former a large number of somites pass over into the new animal, in the latter only. 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
