General principles of zoology . perma-nently, present in all multicellular animals; the latter, onthe contrary, may be completely absent. If the sexualproducts arise in the skin or in the walls of the digestivetract, as is usually the case in the coelenterates, thenspecial outlets are superfluous, since the ripe elements canreach the exterior directly by rupture of their covering orby means of the digestive tract. Germinal Epithelium and Germinal Glands.—Maleand female sexual cells, as we have seen, originate froman undifferentiated incipient organ which is called the ger-minal epithelium. Its
General principles of zoology . perma-nently, present in all multicellular animals; the latter, onthe contrary, may be completely absent. If the sexualproducts arise in the skin or in the walls of the digestivetract, as is usually the case in the coelenterates, thenspecial outlets are superfluous, since the ripe elements canreach the exterior directly by rupture of their covering orby means of the digestive tract. Germinal Epithelium and Germinal Glands.—Maleand female sexual cells, as we have seen, originate froman undifferentiated incipient organ which is called the ger-minal epithelium. Its predilection is to form a part of GENERA L ORGA NO LOG Y. the epithelial covering of the body cavity, in many animalspermanently, in others only temporarily; in the lattercase, it separates, usually by constriction, and forms gland-like bodies, the sexual glands. Gonochorism and Hermaphroditism.—In most ani-mals, the germinal epithelium produces either only femaleor only male sexual cells; such animals are called separate-. —vd di> FIG. 68.—Sexual organs of LumbricMS agricola. (From Lang, after Vogt and Yung.) Theseminal vesicles of the right side are removed. l>»i, ventral nerve-cord ; bv and bl, ventraland lateral rows of setae; st\ sf2, receptacula seminis; j£>, sP, s63, the three seminalvesicles of the left side, which are connected with a median unpaired seminal capsule(s6u). Enclosed in the latter are the anterior and posterior testicles (/z1, /z2), and the an-terior and posterior seminal funnels (z1, z*2), which lead into the vas deferens (vd). a,ovaries; to. ciliated funnels leading into the oviducts {ov); di, remnants of the dissepi-ments ; VIII-XV, eighth to fifteenth segments. sexcd or gonochoristic, in opposition to the hermaphroditicforms, in which both kinds of sexual glands are containedin one and the same individual. Different degrees of her-maphroditism can be distinguished; commonly testes andovary are contained in the same animal, yet sepa
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
