The different forms of embryo amongst the Polyzoa are represented in figs. 130 B, 131, 132, and 133 in what I regard as identical positions, and fig. 133 A is a figure of what may be regarded as an idealized larval Polyzoon. In all the larvæ there is present a ciliated ring, which separates an oral from an aboral face, and is apparently homologous throughout the series. In the adult it is probably represented by the lophophore. On the oral face is situated in all cases the mouth, and in the entoproctous larvæ and Cyphonautes also the anus. It thus appears that Cyphonautes, though the larva of an ectoproctous form, is itself entoproctous--a fact which tends to shew that the Entoprocta are the more primitive forms. In all the larvæ, except possibly those of the Cyclostomata, there is present on the anterior side of the mouth, in the Ectoprocta on the oral, and in the Entoprocta on the aboral side of the ciliated ring, an organ, to which is attached externally a plume of long cilia. This organ has been identified throughout the series in accordance with Hatschek's view as the dorsal organ or rudimentary bud; but it is well to bear in mind that this identification is of a purely hypothetical character. [FIG. 133 A. DIAGRAM OF AN IDEAL LARVA OF A POLYZOON. _m._ mouth; _an._ anus; _st._ stomach; _s._ ciliated disc.] On the aboral side of the ciliated ring there is present in all the larvæ an organ, which has been called the ciliated disc, which is probably homologous throughout the series. It perhaps remains in the adult of Loxosoma as the cement gland, but not in other forms. The Polyzoa present a simple and almost certainly degraded organisation in the adult state; it is therefore more than usually necessary to turn to their larvæ for the elucidation of their affinities, and various plausible suggestions have been made as to the interpretation of the characters of the larvæ. Lankester[126] has suggested that the larvæ are essentially similar to those of Molluscs. He compares the main ciliated ring to the velum, but has ingeniously suggested that it represents not the simple velar ring of most molluscan larvæ, but a more extended longitudinal ring, of which the gills of Lamellibranchiata are supposed by him to be remnants, and to which the Echinoderm larvæ with one continuous ciliated band furnish a parallel. [126] Lankester. "Remarks on the affinities of Rhabdopleura." _Quart. J. of Micro. Science_, Vol. XIV. 1874. The foot he finds in the epistome of the Phylactolæmata, and the disc of Rhabdopleura--both situated between the mouth and anus, and therefore in the situation of the molluscan foot. The peculiar prominence between the mouth and the anus in Pedicellina (_vide_ fig. 130 B) and Loxosoma is probably the same structure.