The embryo of _Tænia elliptica_ similarly gives rise to a Cysticercus infesting the dog-louse (_Trichodectes canis_), without passing through a vesicular condition; but the caudal vesicle disappears, so that it forms simply a scolex. These cases may, it appears to me, be probably regarded as more primitive than the ordinary ones, where the cystic condition has become exaggerated as an effect of a parasitic life. In some cases the larva of a Tænia has a free existence in the scolex condition. Such a form, the larva of Phyllobothrium, has been observed by Claparède[97]. It was not ciliated, and was without a caudal vesicle; and was no doubt actively migrating from an intermediate host to its permanent host. [97] _Beobachtungen üb. Anat. u. Entwick. Wirbell. Thiere._ Leipzig, 1863. Scolex forms, without a caudal vesicle, are found in the mantle cavity of Cephalopoda, and appear to be occupying an intermediate host in their passage from the host of the cystic worm to that of the sexual form. Archigetes, already mentioned, has been shewn by Leuckart (No. 227) to become sexually mature in the Cysticercus state, and thus affords an interesting example of pædogenesis. It is not known for certain whether under normal circumstances it reaches the mature state in another host. _Amphilina._ The early stages of this interesting form have been investigated by Salensky (No. 229), and exhibit clear affinities to those of the true Cestoda. An embryonic provisional skin is formed as in Cestodes; and pole cells also appear. Within the provisional skin is formed an embryo with ten hooks. After hatching the provisional skin is at once thrown off, and the larva, which is then covered by a layer of very fine cilia, becomes free. The further metamorphosis is not known. BIBLIOGRAPHY. _Turbellaria._ (181) Alex. Agassiz. "On the young stages of a few Annelids" (_Planaria angulata_). _Annals Lyceum Nat. Hist. of New York_, Vol. VIII. 1866. (182) Dalyell. "Powers of the Creator." (183) C. Girard. "Embryonic development of Planocera elliptica." _Jour. of Acad. of Nat. Sci._ Philadelphia. New Series, Vol. II. 1854. (184) Alex. Götte. "Zur Entwicklungsgeschichte d. Seeplanarien." _Zoologischer Anzeiger_, No. 4, 1878. (185) P. Hallez. _Contributions à l'histoire naturelle des Turbellariés. Thésis à la faculté des Sciences p. le grade d. Docteur ès-sciences naturelles_, Lille, 1879. (186) Knappert. "Bijdragen tot de Ontwikkelings-Geschiedenis der Zoetwater-Planarien." _Provinciaal Utrechtsch Genootschap van Kunsten en Wetenschappen_. Utrecht, 1865. (187) W. Keferstein. "Beiträge z. Anat. u. Entwick. ein. Seeplanarien von St. Malo." _Abh. d. könig. Gesell. d. Wiss. zu Göttingen._ Bd. XIV. 1868. (188) El. Metschnikoff. "Untersuchungen üb. d. Entwicklung d. Planarien." _Notizen d. neurussischen Gesellschaft d. Naturforscher._ Odessa, Bd. V. 1877. Vide Hoffman and Schwalbe's _Bericht_ for 1878.