OCCURRENCE OF CESTODES IN MAN.[99]—Tape-worms, either in the adult or larval stages (bladder-worms), have, from ancient times, been known to occur in man, and in the animals that serve him as food. Until comparatively recent times, however, the true nature of these parasites, and particularly of "hydatids" (cystic larvae), was unrecognised. Up to the seventeenth century the larvae were regarded as abscesses or diseased growths of the affected organs, and it was only at the close of that century that their animal nature was even suggested. Even at the beginning of the nineteenth century, three modes of origin of Cestodes—by "generatio aequivoca" from the tissues of the body, or by the union of previously distinct proglottides, or again by metamorphosis of free-living worms drunk with water by cattle or birds (as Linnaeus suggested)—were still variously held, at a time when Malpighi, Pallas, and Goeze had recognised the true connexion between the cystic and segmented states of _Taenia crassicollis_ (the cat tape-worm), and when Goeze had seen the eggs of _Taeniae_, and Abildgaard[100] had even conducted the first helminthological experiments (conversion of the larval _Schistocephalus_, Fig. 40, into the adult form). {79}[Illustration: FIG. 39.—A, _Taenia saginata_ Goeze. Nat. size. (From a specimen in the Cambridge Museum.) The approximate lengths of the portions omitted in the drawing are given. At * (after Leuckart) the branched uterus and the longitudinal and transverse excretory vessels are shown. The genital apertures are seen as a lateral opening on each of the larger proglottides. B, Head (scolex) of _T. solium_ Rud. × 12. (After Leuckart.)]