SYSTEMATIC POSITION OF EOZOON.
The unsettled condition of the classification of the Protozoa, and our absolute ignorance of the animal matter of Eozoon, render it difficult to make any statement on this subject more definite than the somewhat vague intimations given in the text. My own views at present, based on the study of recent and fossil forms, and of the writings of Carpenter, Max Schultze, Carter, Wallich, Haeckel, and Clarepede, may be stated, though with some diffidence, as follows:—
I. The class Rhizopoda includes all the sarcodous animals whose only external organs are pseudopodia, and is the lowest class in the animal kingdom. Immediately above it are the classes of the Sponges and of the flagellate and ciliate Infusoria, which rise from it like two diverging branches.
II. The group of Rhizopods, as thus defined, includes three leading orders, which, in descending grade, are as follows:—
(a) Lobosa, or Amœboid Rhizopods, including those with distinct nucleus and pulsating vesicle, and thick lobulate pseudopodia—naked, or in membranous coverings.
(b) Radiolaria, or Polycistius and their allies, including those with thread-like pseudopodia, with or without a nucleus, and with the skeleton, when present, silicious.
(c) Reticularia, or Foraminifera and their allies, including those with thread-like and reticulating pseudopodia, with granular matter instead of a nucleus, and with calcareous, membranous, or arenaceous skeletons.
The place of Eozoon will be in the lowest order, Reticularia.
III. The order Reticularia may be farther divided into two sub-orders, as follows:—