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36 show that they were not perfect animals; and (3), that their exceedingly simple structure differed much from that of the Helminthes. Kölliker, indeed, considered the simple Gregarinæ as unicellular animals. Without assenting to the theory which this expression involves, we may, in the absence of more valid testimony, agree with the general tenor of his observations, and view the Gregarinæ as indubitable members of the group Protozoa. The recent careful investigations of Lieberkühn appear to strengthen this position.

In the same year wherein Leydig published his researches on the Gregarinæ, Professor Huxley described, under the name of Thalassicolla, a singular genus of marine animals, manifesting affinities both with the Sponges and Foraminifera. It would appear, however, that Meyen, seventeen years before, had noted the existence of some of these forms.

The nature of the Thalassicollæ was, subsequently, further elucidated by the late J. Müller, who arranged these organisms under four genera: Thalassicolla proper, Physematium, Sphærozoon, and Collosphæra. He, at the same time, called attention to an allied group of Protozoa, previously unnoticed, which he proposed to term Acanthometra. These observations are, perhaps, the more interesting, since they form the subject of the last communication made to science by this great anatomist.

One other addition to the Protozoa yet remains to be noticed. There can be now little doubt that the Noctiluca of Surriry, well known for its power of imparting a phosphorescent appearance to the sea, and erroneously referred by De Blainville to the Diphydæ, rightly belongs to this sub-kingdom. From the observations of Professor Huxley, its affinities would seem to be nearest the Infusoria, though, by Doyère, Van Beneden, and others, it has been placed with the Rhizopodous members of the group.

Thus, then, there exists an extensive group of organisms of very humble structure, but equivalent in Zoological importance to the Vertebrata, Mollusca, and other primary divisions of the animal kingdom. This department, or sub-kingdom, of Protozoa contains:—


 * , including Foraminifera.
 * , or.
 * , including Psorospermiæ.
 * , or.
 * , including Psorospermiæ.
 * , including Psorospermiæ.