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NATURE AND AFFINITIES OF THE SPONGES. 149disciples of the doctrine of evolution, a far more fascinatinginterpretationof the structure and relationship of these organisms.The following year, that of 1869, was signalized in the annals of thescientific world by the publicationof Professor Ernst Haeckel's brilliantdisquisition in the 'Jenaische Zeitschrift,' Bd. v.1869 (reprintedin the'Annals' for January and February, 1870), in which this talented authorannounced, in the most emphatic terms, that the sponges were more nearlyrelated to the corals, or Anthozoarian Ccelenterata, than to any otherorganized beings, and that the position hitherto assigned to them among theProtozoa was fallacious, and could no longer be maintained. Practically,in the advancement of this theory, Haeckel may be said to have merelyresuscitated and clothed in a new and attractive garb the moribund onethat, first originating with Ellis and Pallas, was still more extensivelydeveloped by Leuckart, but rejected by the verdict of subsequent investigators.This supposed affinity, as advocated by Leuckart and hispredecessors, was, however, one only of broad external isomorphic or homoplasticresemblances. In accordance with their views, each efferent oroscular area in a compound sponge-body was regarded as the equivalentof an individual polyp of a coral stock, minus in each instance thecharacteristic tentacles, stomachal sac, and internalmesenteries and septathat distinguish the representatives of the corals. Summing it up, such alikeness as evoked by Leuckart on the part of the sponges with respect tothe corals may, borrowing a dramatic simile, be aptly compared to theplay of ' Hamlet,' minus the king of Denmark. Professor Haeckel, however,disinterring and infusing new breath into Leuckart's abandoned conception,claimed for it a far wider and more deeply reaching significance.It was insisted upon by the illustrious biologist of Jena that not only ageneral external or homoplastic resemblance existed between the organicgroups in question, but that the internal structure and histological organizationof the two also coincided. Following out this line of argument,it wasrepresented that the nutritive canal system of the sponges was both homologousand analogous with the gastrovascular system of the corals ;thatboth the corals and the sponges were characterized by the possession ofsimilar distinct external and internal cellular layers, or ectoderm andentoderm ;and that the adult organisms were derived in either case fromsimilar primitive diploplastic ciliated larvae, planulce and gastrulce, theseagain being developed from ordinary segmented ova.As may have been anticipated, this bold conceptionof ProfessorHaeckel's inaugurated for the sponges an era of most close and rigidinvestigation not yet ended, which has already resulted in a mass ofevidence that has added vastly to our previous knowledge of the ultimatecomposition of these structures. None of this testimony, however, can besaid to confirm precisely that interpretation of the structural or developmentalphenomena insisted upon by Haeckel. In the majority of instances,indeed, it is entirely subversive of his theory. Among the earliest of