AMEBOID MOVEMENT 129 



purposes in understanding the nature of both flagella and pseudo- 

 pods, it is of special importance for our present purpose because 

 it shows a strong tendency for pseudopods to fall into spirals and 

 to move in spirals. This tendency is found not only in this 

 species of ameba but is observed also occasionally in radiosa 

 (Figure 7, p. 30) and in several other species. In these latter 

 species the pseudopods are stiff and not capable of waving about 

 in the water, as are those of flagellipodia, whether in the spiral 

 shape or not. In radiosa the pseudopods may become spiralized 

 only as a preliminary to withdrawal. It is evident therefore that 

 the spiral urge can express itself best in a plastic pseudopod. 



Taking all these observations together, the tendency of pseudo- 

 pods to move in a spiral manner, the tendency of the ameba as a 

 whole to move in a spiral path when in the flagellate stage, and 

 the wavy path of amebas which is smoothest when in the clavate 

 stage, all these observations seem to confirm the supposition that 

 the wavy path is in reality a flattened spiral, and that the spiral 

 urge in ameba is a very fundamental factor in the process of loco- 

 motion. In other words, there is present in ameba an automatic 

 regulating mechanism controlling the direction of movement so 

 that when free from stimulation a spiral' path is followed. 



Where can such a mechanism be located? In organisms of 

 fixed form, such as vertebrates, the mechanism controlling and 

 coordinating locomotion is in the central nervous system. Even 

 in some protozoa (Enplotes) a motorium has been found whose 

 function apparently is that of coordinating the action of at least 

 some of the motile organs (Sharp, '13, Yocom, '18). But in 

 ameba there is no fixed form. The ameba is continually mixing 

 itself up. No two masses of protoplasm ever occpy the same 

 space relations to each other for more than a moment, excepting 

 perhaps within the nucleus. But the nucleus as a whole is con- 

 tinually changing its position with regard to the rest of the ameba, 

 and almost certainly its position at any given moment in the ameba 

 is he result, not of its own acticity, but of the endoplasm and the 

 ectoplasm. A formed nucleus, moreover, is not necessary to con- 

 certed movement, for Protamoeba, in which no granules of 

 chromatin have been found, and there certainly is no formed 

 nucleus present, moves in a concerted manner, though I am un- 



