THE MOVEMENTS AN T D REACTIONS OF AMCEBA. 173 



properties, not merely of the outer layer, but of the entire substance of 

 the Amoeba, may be a question. The fact that ectosarc and endosarc 

 are mutually interconvertible would seem to imply an affirmative answer 

 to this question, and I believe other evidence could be adduced looking 

 in the same direction. But the locomotion itself seems to require these 

 properties only in the ectosarc, so that we shall for the present leave out 

 of consideration the question as to their existence in the endosarc. 



To the three primary phenomena above mentioned we must devote 

 further attention. It has been maintained by certain writers that the 

 ectosarc is not an elastic and contractile membrane, as above set forth ; 

 hence we must examine the evidence on that point. There then remain 

 the questions : What is the cause of the pushing out at the anterior edge ? 

 and, What is the essential nature of the contractility of the ectosarc? 

 These questions will be reserved for a special section on the theories 

 of amoeboid movement. We will at this point investigate certain 

 general properties of the substance of Amoeba, with a view espe- 

 cially to determining whether we are justified in considering the 

 ectosarc elastic and contractile, though not limiting our attention to 

 these properties alone. 



SOME CHARACTERISTICS OF THE SUBSTANCE OF AMCEBA. 

 FLUIDITY. 



It is, of course, not necessary to dwell upon this point ; it has been 

 treated in detail recently by Rhumbler (1898, 1902) and Jensen (1900). 

 For anyone who is familiar with the movements of Amoeba from per- 

 sonal observation, doubt cannot exist that its protoplasm has at least 

 some of the most striking properties of fluids, notably the property of 

 flowing, with the freedom of movement of the particles with reference to 

 each other that this implies. This applies most strongly to the endosarc ; 

 for the ectosarc, as we shall see, there are decided limitations to the 

 fluidity. Nevertheless, the particles of the ectosarc have, to a considera- 

 ble degree, that freedom of movement with relation to each other that is 

 characteristic of fluids. This is shown, for example, by the fact that any 

 portion of the ectosarc may be temporarily excluded from the advanc- 

 ing stream (especially common at the posterior end, p. 169), and in the 

 fact that neighboring portions of the ectosarc may flow in opposite 

 directions (p. 148) . But the characteristics of the ectosarc are much 

 more those of a tough, rather persistent skin than has sometimes been 

 supposed. This point is brought out in the following sections. 



RHUMBLER'S 'EXTO-ECTOPLASM PROCESS." 



The movements of the outer layer of the body described in this paper 

 have an important bearing on the transformation of endosarc into ecto- 

 sarc and vice versa, of which so much is said in Rhumbler's recent 



