[4] It is possible that Gruber was led to suggest a gelatinous composition for the layer in question on the strength of assertions made by several writers that amebas secrete mucus. It is true that amebas may be displaced by threads of mucus hanging to glass needles which has collected on the needles while manipulating the amebas in the culture medium, but that is not to be taken as evidence that the mucus is secreted by the amebas. Ameba cultures are always full of gelatinous material formed by bacteria. I have not thus far been able to convince myself that amebas actually secrete mucus. [5] According to Ewart (’03) the viscosity of streaming protoplasm in plant cells lies between η = .04 and η = .2. But the velocity of streaming endoplasm in ameba is considerably slower than that in the plant cells which formed the basis for Ewart’s calculations. In comparison, we may estimate the viscosity of the endoplasm of ameba as η = .1 dynes per sq. cm. The velocity of streaming endoplasm, as ascertained by observations on _Amoeba dubia_ (in which the endoplasm flows usually rapidly) 1 is---- cm. per second. 880 Now, given a unit mass of endoplasm moving at a given instant with a 1 velocity of---- cm. per second against viscosity of η = .1 dynes per sq. 880 cm., how far will the unit mass travel before coming to rest? Velocity Force = Mass × Acceleration, and Acceleration = ---------. Time MV η = Viscosity = F = MA = ----. T V Now if M = 1, η = F = A = ----. T 1 V ---- 1 T = ---- = 880 = ----. η ---- 88 .1 The space travelled over in uniformly accelerated motion equals 1 1 1 1 1 S = ---- AT^{2} = ---- × ---- × (----)^{2} = ------ = .00000645 cm. 2 2 10 88 154880 If, therefore, the force moving the central stream of endoplasm should suddenly be discontinued, the resistance offered by the viscosity of the enveloping endoplasm would allow it to move only .0000645 mm. before coming to rest. But the ameba as a whole moves more slowly than the central stream of endoplasm, the average rate of movement being about 1 ----- mm. per second. The effect of the streaming endoplasm on the 300