The demonstration of the most conspicuous and important property of ectoplasm in _Amoeba proteus_ is easily made. With the high power of the microscope one focusses on the upper surface of an active pseudopod, paying especial attention to the small crystals imbedded in the protoplasm. These crystals, although they dance about slightly (Brownian movement) and otherwise change position to a slight extent, nevertheless appear to be held in place by a very viscous medium. Such movement as is observed in these crystals appears more or less erratic; it is not coordinated and it is only by chance in the direction of locomotion of the ameba. While observing the practically stationary crystals of the ectoplasm one can at the same time, though indistinctly, see the forward sweep of the crystals and other granules in the endoplasm below. But observation fails to detect a definite line of separation between the stationary ectoplasm and the mobile endoplasm; the one grades off insensibly into the other. The formation of ectoplasm in _proteus_ is a much more complicated process than in almost any other ameba, excepting the large species _Amoeba carolinensis_[1] discovered by Wilson (’00). We shall have occasion however to refer at length to the method of ectoplasm formation in _proteus_ later on, so we may consider _proteus_ first from this point of view, and then take up a few other species in which the process is simpler. It is a fact more or less familiar to observers of amebas that _proteus_, as distinguished from the other amebas, has a number of large irregular, roughly longitudinal folds or ridges on its pseudopods and on its main body (Figure 3). Under normal conditions these are never absent. They are not found at the free ends of advancing pseudopods, but they take their origin at some little distance from the ends. It is this characteristic of ridge formation that complicates the process of the transformation of endoplasm into ectoplasm; for instead of having to deal with ectoplasm formation at the anterior ends of pseudopods only, we find this process taking place irregularly all over the surface of the ameba. These folds or ridges were first observed by Leidy (’79) and it is an eloquent tribute to the keen observation of this [Illustration: Figure 3. Formation of longitudinal ridges and grooves in the ectoplasm of _Amoeba proteus_. _A_, _B,_ _C_, _D_, showing stages in the development of a single pseudopod. _a_, _b_, _c_, _d_, _d_^{1}, cross sections of pseudopods at the levels indicated. The arrows show the direction of endoplasmic streaming with special reference to the formation of ridges. The numerals 1 to 7 indicate the order in which the ridges were formed. Note the tongues of ectoplasm which extend into the endoplasm, in the cross sections.]