90 AMEBOID MOVEMENT 



and Peloinyxa scheidti; in the next group, with less fluid proto- 

 plasm is Amoeba dnbia; in the third group is A. protons and A. 

 discoides; in the fourth group, with the least fluid protoplasm, 

 come A. radio sa -and A. verrucosa. These groups represent a pro- 

 gressive increase in the amount of ectoplasm in proportion to the 

 endoplasm. There being less water present in the higher groups 

 than in the lower, which follows from a stiffer endoplasm, it is 

 possible for them to form endoplasm, that is, to change phase, 

 more readily. And as a corollary to this we may add that more 

 pseudopods are formed, since ectoplasm can be formed more 

 readily. (The verrucosa types possess very stiff ectoplasm, and 

 they increase their surface by flattening out and by forming longi- 

 tudinal ridges. They cannot for some unknown reason form 

 pseudopods). Again with the increase in the consistency of 

 the protoplasm, the pseudopods become more slender (and stiffer) 

 and more contractile, the most slender pseudopods (radios, flagel- 

 lipodia} being very much more contractile than the larger ones of 

 proteus or discoides, for example. An additional factor operates 

 here, however, for some of the slender pseudopods as of radiosa 

 and bilzi are static and for a great part of their existence prac- 

 tically incapable of contraction. The high development of con- 

 tractility follows, of course, from the high degree of dispersion 

 of the internal phase in ectoplasm, of which these pseudopods 

 almost wholly consist. Thus, many, if not most, of the more 

 generalized peculiarities of form of amebas may be traced to the 

 amount of water in the protoplasm. 



The number of pseudopods in an ameba is an important factor 

 in its method of locomotion, as may readily be perceived. Since 

 amebas generally move with great variation in speed as one com- 

 pares the different species, whether they form very little ecto- 

 plasm or very much, and are able to maintain themselves on 

 their paths, it follows that ectoplasm formation by itself does 

 not play an important part in originating movement. But it 

 requires only a few minutes' observation to see that ectoplasm is 

 necessary to guide the ameba, so to speak, and to make the endo- 

 plasmic stream effective for the purpose of orderly movement. 

 It requires very little imagination to see what would happen if 

 no ectoplasm were present in a limicola or any very fluid ameba. 

 Streaming would undoubtedly occur as before, but the currents 



