. Animal biology. Zoology; Biology. EARTHWORM 235 Lincoln, Nebraska, their burrows have been followed to a depth of more than 18 feet from the surface. In winter they usually remain below frost line. 275. Reproductive System and Reproduction.—Both sets of sex organs (Fig. 139) are present in each individual earthworm, this animal being monecious. The male organs include three pairs of seminal vesicles, the first two of which open into a common central reservoir in the tenth metamere and the third into a similar reservoir in the eleventh metamere. In each reservoir is found a pair of testes. Fr
. Animal biology. Zoology; Biology. EARTHWORM 235 Lincoln, Nebraska, their burrows have been followed to a depth of more than 18 feet from the surface. In winter they usually remain below frost line. 275. Reproductive System and Reproduction.—Both sets of sex organs (Fig. 139) are present in each individual earthworm, this animal being monecious. The male organs include three pairs of seminal vesicles, the first two of which open into a common central reservoir in the tenth metamere and the third into a similar reservoir in the eleventh metamere. In each reservoir is found a pair of testes. From each reservoir vasa efferentia lead into a common vas deferens on each side, the outer opening of which is in metamere XV. The sperm cells are produced in the testes, matured in the seminal vesicles, and passed out through the vasa efferentia and vasa deferentia. Uerve corc^. Fig. 139. SetrJi'na/ recepfac/es — Testis 3e/T7i'na/ ves/c/es Ovary Ovtcfact Vas deferens -Reproductive organs of an earthworm. (From Wieman, "General Zoology," by the courtesy of McGraw-Hill Book Compa7iy, Inc.) The female organs consist of a pair of ovaries in metamere XIII. The egg cells are set free in the coelom and on each side are collected by a ciliated funnel which leads into an oviduct in metamere XIV; this opens to the outside on the ventral surface of this metamere. In addition there are two pairs of seminal receptacles in the ninth and tenth meta- meres, which open to the outside in the grooves between the ninth and tenth, and the tenth and eleventh, metameres. Self-fertilization does not take place in the earthworm, but sperm cells are transferred from one individual to another by a process of copulation. Two worms come together with their ventral surfaces in contact and with their anterior ends pointed in opposite directions (Fig. 140 A), placing themselves so that metameres IX, X, and XI of one worm are opposite the clitellum of the other. They are held together by two slim
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