536 



TRANSFORMATION OF ENERGY 



projections, however, consist frequently of hyaline protoplasm only, destitute 

 of granules, so that the interdependence of internal granular streamings and 

 external alterations in form is somewhat doubtful. 



The simplest form of amoeboid movement is met with in the Amoebae. 

 Pelomyxa, for instance, consists of a flattened, elongated mass of protoplasm, 

 which creeps over the substratum without any great change in form. Centrally 

 we may observe a single axial stream of granules spreading outwards towards the 

 advancing regions of the body of the organism, and the granules in the rear end 

 appear to converge into this axial current, while a zone surrounding the body 

 where the granules are at rest appears to separate the region of confluence behind 

 from the region of effluence in front. Amoeba behaves exactly in the same way 

 (Fig. i68) ; a forward movement appears not only at V, but also in the laterally 

 advancing branches at L and R, so that the granules are seen streaming in three 

 directions. Between V and R a fourth, but subsidiary, current may even be 

 noted, so that there are five zones (indicated by crosses) which are at rest. 



The detailed description of amoeboid movement given above renders the 

 phenomena of movement seen in the protoplasts of the higher plants, which are en- 

 closed in cell-walls, easily comprehensible (Hofmeister, 

 1867). We might, in fact, compare such protoplasts with 

 Myxomycetes enclosed by a membrane. A stationary 

 layer of protoplasm of greater or less thickness always 

 lies immediately in contact with the wall ; next comes 

 a layer of motile protoplasm lying between the vacuole 

 and the peripheral layer, and from this motile layer 

 arise the anastomosing strands and filaments, similar to 

 those seen in a plasmodium, which permeate the cell-sap 

 as with a network and which exhibit continual altera- 

 tions in form and position, although these, owing to the 

 confined character of the cell cavity, are necessarily 

 limited in extent. Just as in the case of the Plasmo- 

 dium, so here also we observe a streaming of granules 

 both in the individual strands and in the peripheral pri- 

 mordial utricle. The direction of these currents varies 

 from time to time and, even in contiguous regions of a 

 strand, may be not infrequently in opposite directions ; in 

 other cases the granules may accumulate all on one side. 

 In addition to these more irregular protoplasmic 

 movements, another type of movement has been distinguished from those just 

 described (circulation) under the name of rotation. In this type of movement 

 the peripheral protoplasm (save an external layer of varied thickness) moves 

 in a constant direction, following, in elongated cells, the long axis of the cell, and 

 often showing obvious torsion if the cell be exceptionally long. The move- 

 ment is most rapid nearest the vacuole, which becomes moved about passively, 

 showing that the cell-wall and the vacuole are to the protoplasm of the cell 

 what the substratum is to the plasmodium. The vacuole acts as a pivot for 

 the movement, and hence the current set up in it is in the reverse direction to 

 those in the protoplasm. 



It is frequently the case that, in addition to setting the minute non-living 

 particles included in the protoplasm in motion, rotation and circulation also 

 bring about, passively, alterations in position of the organs of the cell, i. e. the 

 nucleus and the chloroplasts, and these changes in situation are often of great 

 importance in the plant economy. 



Owing to the widespread occurrence of the movements described and to 

 their obvious importance, attempts have for long been made to discover the fac- 

 tors concerned in them, and not only to correlate amoeboid with the obviously 

 related rotatory and circulatory movements, but to include under the same 



Fig. 168. Movements in 

 Amoeba. The arrows indicate 

 the direction and rapidity of 

 the streaminor; the crosses 

 mark places where no move- 

 ments are taking place. From 

 the Bonn Textbook. 



