Now on this I have to remark, in the first place, that the two families Amœbina and Actinophryna, which are associated in the order Proteina, differ essentially from each other in several particulars which seem to me of great; physiological importance; whilst I cannot trace any such peculiar bond of union between them, as would be required to justify their separation from all other Bhizopods and their association into a separate order. Again: the foregoing arrangement follows that of Prof. Müller in dissociating Actinophryna from Acanthometrina, to which they are much more nearly allied than they are to Amœbina. And thirdly, the ordinal separation of Gromida from Foraminifera seems to me to be altogether unwarranted by any essential difference, since the condition of the animal in these two groups is in every respect the same ; while the diversity in the material of the envelopes which they respectively form can no more be admitted as a valid ground of separation in this group than in the family Amœbina, of which Arcella exudes a chitinous test like that of Gromia, whilst Difflugia forms its test by the cementation of foreign particles, as do several genera among Foraminifera.
It is, as it seems to me, in the structural and physiological conditions of the animal alone, that we should look for the characters on which our primary subdivisions should be constituted; and notwithstanding that the extreme simplicity and apparent vagueness of those conditions at first sight appear almost to forbid the attempt to assign to them a differential value, yet a sufficiently careful scrutiny will make it clear that, under their guidance, lines of demarcation may be drawn, as precise as in any other great natural group, between three aggregations of forms which assemble themselves round three well-known types, Amœba, Actinophrys, and Gromia,—the sarcode-bodies of these three types presenting three distinct stages in the differentiation of the protoplasmic substance of which they are composed, and exhibiting, in virtue of that differentiation, three very distinct modes of vital activity.
I.—The lowest stage of this differentiation is seen in Gromia and its allies, among which may be particularly specified a remarkable naked form, which has been described by MM. Claparède and Lachmann under the name of Lieberkühnia, and which seems either identical with the Pamphagus of the late Prof. Bailey (U.S.), or very closely allied to it. In this type the whole substance of the body and of its pseudopodian extensions is composed of a homogeneous, semi-fluid, granular protoplasm, the particles of which, when the animal is in a state of activity, are continually performing a circulatory movement, which has recently been likened by Prof. Schultze (and, as it seems to me, with great justice) to the circulation of the particles in the protoplasmic network within the cell of a Tradescantia. The entire absence of anything like a membranous envelope is evinced by the readiness with which the pseudopodian extensions fuse together whenever they come into contact, and with which the principal branches subdivide into finer and yet finer threads, by whose continual inosculations a net-
