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466 especially as this last is often replaced, either partially or completely, by an envelope formed by the cementation of sandy particles.

Thus, then, Amœba and its allies are distinguished from the Actinophryna, by the yet higher manifestation of that tendency to differentiation of the homogeneous protoplasma, which marks so definite a distinction between the Actinophryna and the Gromida; and the distinction is indicated in the former case, as in the latter, by the nature of the pseudopodian expansions, the lobose form of which seems so characteristic of all the typical Amœbina, that they may be appropriately ranged under the ordinal designation. It is quite true that these distinctions do not hold good in every instance; as there are osculant forms (such as the Amœba porrecta of Schultze) whose characters are so intermediate between those of the typical Amœba and of the typical Actinophrys that it is difficult to say to which type they are most nearly allied. And in like manner, judging from the characters of the pseudopodia in Schultze's genera Lagynis and Squamulina, it may be doubted whether the true place of those genera is in association with the Foraminifera, or whether their relation is not really more intimate with the Actino- phryna. But the existence of such osculant forms by no means invalidates the principle of our classification, since their presence only serves to supply, between the Orders into which I propose to divide the Rhizopoda, the link which is necessary to their completeness as natural groups.

It is an. interesting exemplification of the intimacy of the relation between the form of the pseudopodia and the properties of the sarcode-body of the Rhizopoda, that any small separated portion of that body will behave itself after the characteristic fashion of its type; thus, if the shell of an Arcella be crushed, so as to force out a portion of its sarcode, and this be detached from the rest, it will soon begin to put forth lobose extensions like those of an Amœba; whilst if the like operation be performed upon a Polystomella, or any other of the Foraminifera, the detached fragment of the protoplasm will extend itself into delicate ramifying and inosculating pseudopodia, resembling those of Gromia. And this fact seems to me to afford an additional justification of the employment of the characters furnished by the pseudopodia as the basis of a systematic arrangement of the class. The characters of the three Orders into which I propose to distribute its various forms may be concisely summed up as follows:—

I.. The body composed of homogeneous granular protoplasm, without any distinction into ectosarc and endosarc; neither nucleus nor contractile vesicle; pseudopodia composed of the same substance as the body, extending and multiplying themselves by minute ramification, and inosculating completely wherever they come into contact; a continual circulation of granular particles throughout the viscid substance of the body and its extensions. This Order consists of the Foraminifera and the Gromida, whose mutual relations will be presently examined.