(216) E. Zeller. "Untersuchungen ü. d. Entwick. u. Bau d. Polystomum integerrimum." _Zeit. f. wiss. Zool._ Vol. XXII. 1872. (217) E. Zeller. "Weitere Beiträge z. Kenntniss d. Polystomen." _Zeit. f. wiss. Zool._ Vol. XXVII. 1876. _Cestoda._ (218) Ed. van Beneden. "Recherches sur la composition et la signification d. l'oeuf." _Mém. cour. Acad. roy. Belgique._ Vol. XXXIV. 1868. (219) P. J. van Beneden. "Les vers Cestoïdes considérés sous le rapport physiologique embryogénique, etc." _Bul. Acad. Scien. Bruxelles._ Vol. XVII. 1850. (220) T. S. Cobbold. Entozoa. Groombridge and Son, 1864. (221) ---- _Parasites; a treatise on the Entozoa, etc._ Churchill, 1879. (222) Th. H. Huxley. "On the Anatomy and Development of Echinococcus veterinorum." _Proc. Zool. Soc. Vol._ XX. 1852. (223) J. KNOCH. "Die Naturgesch. d. breiten Bandwürmer." _Mém. Acad. Imp. Pétersbourg_, Vol. V. Ser. 7, 1863. (224) F. Küchenmeister. "Ueber d. Umwandlung d. Finnen Cysticerci in Bandwürmer (Tænien)." _Prag Vierteljahrsschr._ 1852. (225) ---- "Experimente üb. d. Entstehung d. Cestoden. 2o Stufe zunächst d. Coenurus cerebralis." Günsburg, _Zeitsch. klin. Med._ IV. 1853. (226) R. Leuckart. _Die Menschlichen Parasiten_, Vol. I. Leipzig, 1863. Vide also additions at the end of the 1st and 2nd volume. (227) R. Leuckart. "Archigetes Sieboldii, eine geschlechtsreife Cestodenamme." _Zeit. f. wiss. Zool._, Vol. XXX. Supplement, 1878. (228) El. Metschnikoff. "Observations sur le développement de quelques animaux (Bothriocephalus proboscideus)." _Bull. Acad. Imp. St Pétersbourg_, Vol. XIII. 1869. (229) W. Salensky. "Ueb. d. Bau u. d. Entwicklungsgeschichte d. Amphilina." _Zeit. f. wiss. Zool._, Vol. XXIV. 1874. (230) Von Siebold. Burdach's _Physiologie_. (231) R. von Willemoes-Suhm. "Helminthologische Notizen." _Zeit. f. wiss. Zool._, Vol. XIX. XX. XXII. 1869, 70 and 73. CHAPTER VIII. ROTIFERA. For many reasons a complete knowledge of the ontogeny of the Rotifera is desirable. They constitute a group which retain in the trochal disc an organ common to the embryos of many other groups, but which in most other instances is lost in the adult state. In the character of the excretory organs they exhibit affinities with the Platyelminthes, while in other respects they possibly approach the Arthropoda (_e.g._ Pedalion ?). The interesting _Trochosphæra æquatorialis_ of Semper closely resembles a monotrochal polychætous larva. Up to the present time our embryological knowledge is mainly confined to a series of observations by Salensky on _Brachionus urceolaris_, and to scattered statements on other larval forms by Huxley, etc.