28 



AMEBOID MOVEMENT 



(Figure n, C) the clavate stage of locomotion is comparatively 

 rare, but when it is found it is observed that the transformation 

 of endoplasm into ectoplasm at the anterior end is incomplete, 

 and the endoplasm seems to be of very liquid consistency. This 

 ameba is characteriezd by the possession, usually, of numerous 

 pseudopods extending from a central mass of protoplasm. In 

 this stage it possesses no main pseudopod as does proteus, dis- 

 coides, laureata and other species, but there are three or four 

 pseudopods extending actively in the general direction of loco- 

 motion. The physical characteristics of these pseudopods, in so 

 far as streaming is affected, are different from those of the clavate 

 amebas. The ectoplasmic tubes are relatively thicker, the endo- 

 plasm is less fluid, and new pseudopods are not formed so readily. 

 It appears therefore that an increase of surface in the ameba 

 serves to increase the amount of ectoplasm that is formed during 

 locomotion. 



There is another group of amebas in which the endoplasm is 

 much more fluid than in dubia. To this group belong Amoeba 

 limicola (Figure 5) and Pelomyxa, schiedti (Figure 6). The 

 latter never forms pseudopods, and the former does so very sel- 

 dom. A. limicola is extremely fluid, and in locomotion the flow 

 of the endoplasm can hardly be called streaming, for it rushes 

 about in the body as if it were only partially under control. The 



Figure 5. Amoeba limicola, after Penard. Figures a, b, e, illustrate the 

 "eruptive pseudopods" by means of which this ameba moves, f, a variety 

 or separate species whose ectoplasm is somewhat firmer, and whose 

 posterior end possesses a conspicuous uroid. c, the nucleus found in 

 a, b, e. d, the nucleus found in /. 





