II. radiolaria. Incipient differentiation of the protoplasmic substance into endosarc and ectosarc, the former semi-fluid and granular, the latter more tenacious and pellucid; a nucleus and contractile vesicle; pseudoppdia rod-like, usually tapering from base to point, composed of the same substance as the ectosarc, exhibiting little disposition either to ramify or to coalesce, haying a more or less regular radiating arrangement, and not showing any constant circulation of granules in their subatance, although a movement of particles adherent to their exterior is often to be distinguished. The type of this order is Actinophrys, constituting, with its immediate allies, the family Actinophryna; but the Order also includes the Acanthometrina, Polycystina, and Thalassicollina, by the last of which this group is connected with the Sponges.
III. Lobosa. More complete differentiation of the protoplasmic substance into endosarc and ectosarc, the former being a slightly viscous granular liquid, and the latter approaching the tenacity of a membrane: a nucleus and contractile vesicle; pseudopodia few and large, being in reality lobose extensions of the body which neither ramify nor coalesce, having well-defined margins, and not exhibiting any movement of granules on their surface, the circulation in their interior being entirely dependent on the changes of form which the body undergoes as a whole. This Order is composed of but a single family, the Amœbina; and it is the one which presents the nearest approximation to the classes Infusoria and Gregarinida.
Having thus explained what I conceive to be the true relations of the Foraminifera to other Rhizopods, I purpose now to state the views to which I have been led by the same mode of enquiry, in regard to the classification of that group. And in the first place, it is requisite to examine what is the physiological value of the separation of the Monothalamous, or Unilocular, forms from the Polythalamous, or Multilocular,—a separation which has been hitherto adopted by all systematists as one of primary importance, although Professor Reuss has lately expressed himself doubtfully as to the correctness of its principle.
There can be no doubt that, in common with all the lower forms of animal as well as vegetable life, the Rhizopoda tend to multiply by a separation of continuously-growing parts of their bodies, which may take the form either of fission or of gemmation, according as the original body undergoes subdivision, or as it puts forth an extension which eventually detaches itself. Among the Foraminifera proper, whose bodies are enclosed in unyielding shells, multiplication by fission cannot take place, except in that early stage of existence in which the shell is not yet consolidated; but extension by gemmation may go on without limit, the successively-formed gemmæ usually remaining in connection with each other and with their stock. The progressive growth of the sarcode-substance causes a portion of it to project beyond the aperture of the shell; and this projecting portion
