MOVEMENTS Ol- AMCEBsE 311 



spondenee with the interpretation of tin- phenomena of 

 streaming movements in the drops of foam, in tin; Ian 

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

 enchylema is poured out upon the five, 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 Amoeba:', 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. 



o 



In the formation of a finger-shaped pseu- 

 dopodium of Aumlm prutcus (Fig. 21) it 

 can be seen that the current which traverses 

 the axis of the pseudopodium and flows 



r 1 !_, . 1 . 



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 Pclomyxa viridis, that the alveoli or 

 "vesicles," observed by him in the protoplasm of this llhixopod, do not bur>t 

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

 that this observation opposes my view as to the causes of ama-boid 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 an- 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 liner protoplasmic structure, 

 Bourne has observed nothing. What these grem '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 dillicult, if all the oth.-r 

 known relations are taken into account, to suppros tin- notion that they are 

 nothing more or less than Zoochh-rella-. 



