466 OKIGENAL ARTICLES. 



especially as this last is often replaced, either partially or completely, 

 by an envelope formed by the cementation of sandy particles. 



Thus, then, Amoeba 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 Amoebina, that they 

 may be appropriately ranged under the ordinal designation Lobosa. 

 It is quite true that these distinctions do not hold good in every 

 instance ; as there are osculant forms (such as the Amoeba porrecta 

 of Schultze) whose characters are so intermediate between those of 

 the typical Amoeba 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 Ehizopoda, the link which is necessary to their complete- 

 ness 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 sar- 

 code-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 Amoeba ; 

 whilst if the like operation be performed upon a Polystomella, or 

 any other of the Eoraminifera, the detached fragment of the proto- 

 plasm 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. Beticulaeia. 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 them- 

 selves 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. 



