OF THE RHIZOPODA IN GENERAL. 13 



which present the most characteristic types of the group, such, for example, as the 

 Actinoplirys. 



4. The designation of this Class (first conferred by M. Dujardin, xxxiii, in 1835, upon a 

 portion of the animals now included in it, which he ranked only as a family of Ivfusoria) is 

 founded upon the power just referred to, which is possessed by all the members of it in a 

 greater or less degree, of putting forth indefinite extensions of the substance of the body, — 

 sometimes short, broad, and rounded — sometimes longer, slenderer, and gradually tapering to 

 a point — sometimes immensely elongated, and narrowed to threads of extreme tenuity, — which 

 are continually varying both in number, form, and dimensions, and which can be altogether 

 retracted, so as to become incorporated again with the body-substance. These diverging 

 processes, termed pseudopodia, are used in some instances merely for the prehension of food ; 

 in some cases, again, their primary office is to move the body from place to place in search of 

 aliment ; whilst, in another set of cases, they seem to be subservient to both functions : and 

 as they bear some resemblance on the one side to the ramifying roots of a tree, on the other 

 to the feet or locomotive appendages of higher animals, the term Rhizopoda, or "root-footed," 

 applied to the class of creatures of which their presence is so distinctive a characteristic, is by 

 no means unexpressive. 



5. The soft and almost homogeneous substance of which the body of these animals is 

 composed, received from M. Dujardin the designation sarcodc, or rudimentary flesh ; and this 

 designation may be conveniently used, if it be duly kept in mind that " sarcode " is not a 

 substance sui generis, but is nothing else than the protoplasm* in which every form of animal 

 structure has its origin, and from which it is evolved by a process of gradual differentiation. 

 This substance is composed of an albuminoid base, with oil-particles in a state of very fine 

 division diffused through it ; it is tenacious, extensible, and contractile ; it is diaphanous, 

 reflecting light rather more than water but less than oil ; and it is dissolved by alkalies (the 

 aid of heat being necessary if a weak solution be used), rendered perfectly transparent by 

 acetic acid, and dyed brown by iodine. In the midst of this substance are usually to be 

 seen vacuoles, or cavities, containing a thinner fluid, which is often coloured ; these are 

 extremely variable, both in number and size, and their deficiency in any definite limiting walls 

 is rendered obvious by their not unfrequent coalescence.f There may generally be observed, 

 in the bodies of Ithizopods, some differentiation between their central and their peripheral 

 portion ; the substance of the latter being the more pellucid, consistent, and motile, whilst 



* That the " sarcode " of Dujardin is nothing more nor less than animal protoplasm not yet 

 differentiated into cell-wall and cell-contents — a doctrine which has recently been put forth as new by 

 Professor Schultze (scix),- — was distinctly stated by the Author iu 1856 (see his Manual entitled 'The 

 Microscope and its Revelations/ chap. ix). 



f These " vacuoles," which commonly form themselves around the particles taken in as food, 

 were mistaken by Professor Ehrenberg under the influence of his " polygastric " hypothesis, for 

 multiple stom.ichs, each having its own proper wall, and opening into a common alimentary canal, 

 ■which commences and terminates by a definite orifice. This notion, as will hereafter appear, is alto- 

 gether ideal, and is utterly inconsistent with the real facts of the case. 



