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:-- (_a_) _Perforata_--having calcareous skeletons penetrated with pores. (_b_) _Imperforata_--having calcareous, membranous, or arenaceous skeletons, without pores. The place of Eozoon will be in the higher sub-order, _Perforata_. IV. The sub-order _Perforata_ includes three _families_--the _Nummulinidæ_, _Globigerinidæ_, and _Lagemdæ_. Of these Carpenter regards the Nummulinidæ as the highest in rank. The place of Eozoon will be in the family _Nummulinidæ_, or between this and the next family. This oldest known Protozoon would thus belong to the highest family in the highest sub-order of the lowest class of animals. THE LATE SIR WILLIAM E. LOGAN.