If it is eventually proved by further experiments on the nutrition of sponges, that digestion is mainly carried on by the general cells lining the passages and the mesoblast cells, and not for the most part by the ciliated cells, it is clear that the epiblast, mesoblast and hypoblast of sponges will not correspond with the similarly named layers in the Coelenterata and other Metazoa. The invaginated hypoblast will be the respiratory layer and the epiblast and mesoblast the digestive and sensory layers; the sensory function being probably mainly localized in the epithelium on the surface, and the digestive one in the epithelium lining the passages and in the mesoblast. Such a fundamental difference in the primary function of the germinal layers between the Spongida and the other Metazoa, would necessarily involve the creation of a special division of the Metazoa for the reception of the former group. BIBLIOGRAPHY. (122) C. Barrois. "Embryologie de quelques éponges de la Manche." _Annales des Sc. Nat. Zool._, VI. ser., Vol. III. 1876. (123) Carter. "Development of the Marine Sponges." _Annals and Mag. of Nat. Hist._, 4th series, Vol. XIV. 1874. (124) Ganin[71]. "Zur Entwicklung d. Spongilla fluviatilis." _Zoologischer Anzeiger._ Vol. I. No. 9, 1878. (125) Robert Grant. "Observations and Experiments on the Structure and Functions of the Sponge." _Edinburgh Phil. J._, Vol. XIII. and XIV., 1825, 1826. (126) E. Haeckel. _Die Kalkschwämme_, 1872. (127) E. Haeckel. _Studien zur Gastræa-Theorie._ Jena, 1877. (128) C. Keller. _Untersuchungen über Anatomie und Entwicklungsgeschichte einiger Spongien._ Basel, 1876. (129) C. Keller. "Studien üb. Organisation u. Entwick. d. Chalineen." _Zeit. f. wiss. Zool._, Bd. XXVIII. 1879. (130) Lieberkühn. "Beitr. z. Entwick. d. Spongillen." Müller's _Archiv_, 1856. (131) Lieberkühn. "Neue Beiträge zur Anatomie der Spongien." Müller's _Archiv_, 1859. (132) El. Metschnikoff. "Zur Entwicklungsgeschichte der Kalkschwämme." _Zeit. f. wiss. Zool._, Bd. XXIV. 1874. (133) El. Metschnikoff. "Beiträge zur Morphologie der Spongien." _Zeit. f. wiss. Zool._, Bd. XXVII. 1876. (134) El. Metschnikoff. "Spongeologische Studien." _Zeit. f. wiss. Zool._, Bd. XXXII. 1879. (135) Miklucho-Maklay. "Beiträge zur Kenntniss der Spongien." _Jenaische Zeitschrift_, Bd. IV. 1868. (136) O. Schmidt. "Zur Orientirung über die Entwicklung der Schwämme." _Zeit. f. wiss. Zool._, Bd. XXV. 1875. (137) O. Schmidt. "Nochmals die Gastrula der Kalkschwämme." _Archiv für mikrosk. Anat._, Bd. XII. 1876. (138) O. Schmidt. "Das Larvenstadium von Ascetta primordialis und Asc. clathrus." _Archiv für mikrosk. Anatomie_, Bd. XIV. 1877. (139) F. E. Schulze. "Ueber den Bau und die Entwicklung von Sycandra raphanus." _Zeit. f. wiss. Zool._, Bd. XXV. 1875. (140) F. E. Schulze. "Zur Entwicklungsgeschichte von Sycandra." _Zeit. f. wiss. Zool._, Bd. XXVII. 1876.