MOVEMENTS OF AMCEB^E 311 



spondence with the interpretation of the phenomena of 

 streaming movements in the drops of foam, in the fact 

 that, by the bursting of some of the superficial alveoli, 

 enchylema is poured out upon the free surface of the proto- 

 plasmic body, where it produces a local diminution of 

 surface tension, and in this way sets up an extension 

 centre together with forward movement. 1 In this way 

 are explained not only simple amoeboid movements, from 

 which we started, but also more complicated movements 

 and changes of form by means of finger-shaped pseudo- 

 podia. The formation of such pseudopodia takes place 

 with phenomena of streaming movement corresponding 

 perfectly to those which go on throughout the body of an 

 Amoeba which streams in a simple manner ; in these 

 pseudopodia it is therefore merely a matter of local extension-^ 

 currents, reaching over a short distance only. 



In Amoebae, however, an additional circumstance seems 

 to come into play, as has already been pointed 

 out above, which has the effect of produc- 

 ing a limitation in the extension -currents. 

 In the formation of a finger-shaped pseu- 

 dopodium of Amoeba proteus (Fig. 21) it 

 can be seen that the current which traverses 

 the axis of the pseudopodium and flows 



L * Fig. 21. 



away on all sides from its tip, comes to rest 



at a very short distance behind the tip a circumstance 



which in any case is extremely favourable to the rapid 



1 A. G. Bourne lias pointed out, in an investigation that has recently 

 appeared upon the newly-discovered Pdomyxa viridis, that the alveoli or 

 "vesicles," observed by him in the protoplasm of this Rhizopod, do not burst 

 in the movement, or rather in the development of pseudopodia ; he thinks 

 that this observation opposes my view as to the causes of amceboid movements. 

 In answer to this I must state explicitly that the "vesicles" described by 

 Bourne certainly have nothing whatever to do with the true alveoli of the 

 protoplasm. They are spherical structures filled with green contents, and 

 their considerable size must alone exclude a comparison with the true alveoli 

 of protoplasm. Of the true, and very much finer protoplasmic structure, 

 Bourne has observed nothing. What these green "vesicles" really were 

 I will not here further inquire, though in spite of assertions to the contrary 

 made by the discoverer of Pdomyxa viridis, it is difficult, if all the other 

 known relations are taken into account, to suppress the notion that they are 

 nothing more or less than Zoochlorellje. 



