CHAPTER VIII 

 ON THE NATURE OF THE SURFACE LAYER 



The observations in the preceding chapters on the general 

 movements of the surface layer of amebas will afford a sufficient 

 basis for an inquiry into the nature of this layer. The mere 

 demonstration of the existence of this layer is, of course, interest- 

 ing enough, for a number of contradictory statements by various 

 students of the amebas are satisfactorily cleared up by these ob- 

 servations. But the problem of ameboid movement affects other 

 organisms besides amebas, and since the movement of the surface 

 layer is so intimately associated with ameboid movement, it be- 

 comes of more than ordinary interest to learn something of the 

 nature and composition of this layer. 



In the first place the property of carrying particles toward the 

 anterior end of amebas does not appear to be of any advantage. 

 That is, whatever the movements of the outer layer may be, the 

 ameba does not appear to be better off when particles are carried 

 forward than when none are carried, for such particles are very 

 small and almost without exception devoid of food value. The 

 particles are masses of debris which accidentally adhere to the 

 ameba, and the ameba makes no visible effort to make such par- 

 ticles adhere, nor to get rid of them. The ameba seems to be 

 quite indifferent to the presence of such particles. 



On the other hand, as Schaeffer ('17) has pointed out, the 

 capacity for transporting particles cannot but be looked upon as 

 a hindrance to locomotion. As has been stated, the surface film 

 moves in the same direction as the ameba'. Whenever the surface 

 film comes against a solid object, it pushes against the object, and 

 nullifies to a certain, though small, extent the energy expended in 

 moving forward. And it will be seen without further argument, 

 of course, that the energy involved in carrying particles forward 

 is not only itself lost but consumes an appreciable part of the 

 energy available for forward movement. This fact, together with 

 the universal occurrence of this phenomenon among amebas indi- 



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