OF THE RHIZOPODA, 337 



figures the capture, swallowing, and digestion of an Amoeba verrucosa by a cannibal (A. proteus). 

 Elsewhere Dr. Leidy gives an account of another capture: "In one instance I saw an 

 individual (A. proteus) containing, within a large vacuole, an active Infusorian (a Urocentrum), 

 and having a second victim of the same kind included in the fork of a pair of pseudopods, the 

 ends of which were brought into contact, so as to imprison the animalcule within a circle. 

 The latter moved restlessly about within its prison, but after a time became motionless, and 



shortly after the ends of the pseudopods which enclosed it fused together Fibres 



of ectosarc extended from the body of the Amoeba towards the fused ends of the pseudopods, 

 and finally the Urocentrum was enclosed in a vacuole like that in the interior of the body of 

 the Amoeba. Having carefully watched the latter for some time, the two vacuoles containing 

 the captured Urocentrums were seen gradually to diminish in size, the contents were reduced 

 to the usual size of the ordinary food-balls of the endosarc, and all trace of the previous character 

 of the victims was completely lost." Dr. Leidy adds that " the different food-materials undergo 

 chemical changes as a result of digestion in the endosarc, and colours become changed in a 

 striking manner. The bright green chlorophyll of Algae becomes brown or yellow, and shrivelled within 

 the colourless cells ; and the endoehrome of Diatoms becomes browner in tint, and shrivelled into 

 two narrow strings within each shell." 



Dr. Wallich has watched the process of a Furcularui eating pieces out of an Amoeba ; but he has 

 also seen this Rotifer a prey to an Amwba. 



VII. In the foregoing remarks on the Rhizopoda, we have alluded to one of the simplest 

 (Protamceba, Fig. 2), and to one of the most highly developed (Amoeba, Figs. 1, 3), for the 

 convenience of describing both the general and the essential characters of the sarcodic elements 

 belonging to the whole group. In entering on a description of the other special forms, it would be 

 technically correct to begin with the simplest and to proceed to the more advanced. But, in the first 

 place, it is best for genei-al observers to have some notion of that Rhizopod (Amoeba) most commonly 

 met with. Secondly, the order of any natural group is little like a straight line, but far more 

 resembles a network, or a reticulate series of rings touching each other, on account of passages and 

 gradations among characters, features, and structures not essential to strict zoological distinction, 

 but analogies only, or homologies, nevertheless striking and useful to the student in remembering 

 tabulated arrangements. Thirdly, whilst internal organs cannot always be readily seen, the external 

 visible character of shelled or shell-less, of skeleton or no skeleton, of long or short, thick or thin 

 pseudopods, of creeping, swimming, or stationary habits, at once takes the attention of the amateur, 

 and serves to direct him to the right family and order. 



Several classifications have been suggested, mainly on the difference of general shape and of 

 pseudopodial elongations, on the variations of ectosarcal consistency, and difference of tests and 

 skeletal supports. These plans have been noted and reviewed by Wallich, Leidy, Glaus, and others. 

 Dr. Wallich, however, has pointed out the grounds on which a really natural classification of the 

 Rhizopoda should be founded, namely, on the absence or presence of what appear to be specially 

 differentiated parts of the sarcode, such as the nucleus and the contractile vesicle. These structures, 

 elementary as they are, he believes to be indications of progressive organisation, and, as such, to afford 

 a good structural and physiological basis for grouping the allied creatures in zoological order. Thus, 

 first, those which have neither a definite nucleus nor a contractile vesicle he terms Herpnemata 

 (creep-threads), such as the Foraminifera (hole-bearers), with calcareous shell, and the Polycistina 

 (many baskets), with silicious skeleton ; secondly, those which have a definite nucleus, but no 

 contractile vesicle, are his Protodermata (first-skins), of which some have their skeleton of solid 

 silicious spicules and rays (Plagiacanthidie, Acanthometrina, Thalassicolliiia), and others have 

 a silicious skeleton of tubular fibres (Dictyochidce) ; thirdly, those Rhizopods which possess 

 both the organs mentioned above form the highest group, viz., the Proteina (Proteus-like). 

 These are divisible by their pseudopods being either (1) " monomorphous " (single-shape), or 

 (2) "polymorphous" (many-shape). The former division are the Actinopkryna ; the latter are 

 the A-iHcebii<". 



For the reasons above stated, using the word " Rhizopoda " for the whole group, we will take 

 them in order, from the Amoeba downwards, with little violence to Dr. Wallich's system, though 

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