206 GENEEAL HISTORY OF THE INFUSOEIA. 



the notice of microscopists on account of its bearing on the question of cell- 

 constitution. 



The variable processes serve the Rhizopoda for locomotive organs. An ex- 

 pansion is thro^vn out in advance, into which a constant influx of the sarcode 

 substance sets, — whilst in the opj^osite direction a counter- current occurs, 

 effecting the retraction of the posterior processes. This onward flow of the 

 substance of the body proceeds until at length the whole is transferred into 

 the advanced process, mo^dng from its base to its termination. In this manner 

 the animal progresses, the space passed over equalling the length of the ex- 

 pansion it protrudes. This method of locomotion may be designated creep- 

 ing or crawling, and is the only one with which this class of animals is en- 

 dowed. The consequence is that they are, as a rule, to be only foimd adherent 

 to solid bodies, and cannot move by swimming. However, they can move as 

 passive particles of matter, be rolled along by currents upon any substance 

 they are in contact with, or, from being (as in the case of Amoeba) of almost 

 the same specific gra\'ity with the water in which they hve, may float, or be 

 suspended in it for a long time. Theii^ motion by creeping is exceedingly 

 slow, and oftentimes is appreciable only by attentive watching. 



The graphic description of Schultze, of the expansion of processes in a naked 

 Amoeba and in a testaceous species, viz. the Gromia oviformis, will make the 

 phaenomenon more distinct. The former is a new species discovered and named 

 by himself the Amoeba porrecta (XXI. 3). It is distinguished from other 

 species in the genus by the great extension it is capable of, and by the lively 

 motile energy of its contractile substance. " It sends out from its colourless 

 body, on all sides, numerous fibrous processes, short and broad on theii' fii\st 

 extrusion, but which gradually elongate until they exceed the diameter of 

 the body eight or ten times, and taper to such fine extremities that a mag- 

 nifying power of 400 diametei^ is needed to distinguish them. The figui'e 

 and extension of the body change every moment, according to the side in 

 which the ramifications are extended. If two or more of the filiform pro- 

 cesses touch, a coalescence takes place, and broader plates or net-like inter- 

 lacements are produced, which, in the continual changes of figm^e, are either 

 taken up again into the general mass, or otherwise are fui'ther increased by a 

 fresh influx of matter, until finally the entire body is transposed to their place." 



In the testaceous Gromia ovifornnis (XXI. 16), after a state of rest of some 

 dm^ation, fine fibrous processes are seen to be extended from the single large 

 opening of the shell, which, on their first extrusion, move about in a groping 

 manner until they lay hold of some solid body (such as the siuface of the glass 

 slide) on which they may stretch themselves out, receiving in the meanwhile 

 new matter from within the shell. The first fibres are extremely fine ; but pre- 

 sently they grow wider, and proceed to elongate themselves, pm^suing a straight 

 course, ramifj-ing in their own way and coalescing with adjoining processes, 

 until, becoming progressively finer and finer, they attain a length exceeding 

 that of the body six or eight times. The fibres having now outstretched 

 themselves in eveiy dii^ection, and absorbed the greater part of the finely- 

 granular contractile substance, their further extension in length ceases. 

 However, the reticulations go on miiltiplying ; numerous bridges (inoscula- 

 tions) are estabhshed between them ; and by the continued changes of position 

 a constantly shifting protean web is produced, where a greater number of 

 fibres come together at the periphery of the sarcode-net as we may term it, 

 broader plates (lanunae) of the perpetually-flowing substance are formed, from 

 which again new filaments are pushed out in new directions, as if it were a 

 separate Amoeba. In the PoJi/stomelhe, the long fibres are seen to converge 

 to form a pyramidal i)undlc, and to coalesce into wide laminte at its apex. 



