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Perhaps none of the factors influencing the streaming of the endoplasm mentioned above exercises as profound and constant an influence as its capacity to form ectoplasm. As has been intimated earlier (p. 3–9) streaming as observed during locomotion is not supposed to be possible at all unless accompanied by the formation of ectoplasm at the forward ends of pseudopods, and its transformation into endoplasm at the posterior end of the ameba. We may therefore next consider the rôle ectoplasm plays in locomotion, and in some other fundamental activities of the ameba.

In the first place it is necessary to define the word ectoplasm, for two entirely different meanings are sometimes given to it. It is used often to designate the clear non-granular layer of protoplasm which thinly covers some of the commoner amebas, and is especially prominent in some of the small species, where the larger part of the anterior end often consists of protoplasm quite free from granules. The other use to which the word is put is to designate the layer of protoplasm on or near the outside of the ameba which is more or less rigid and motionless, resembling the gel state of a colloid. It is the latter meaning that is given the word as used in this discussion, while I shall follow Jennings (’04) and other, earlier, writers in using the word hyaloplasm in speaking of the outer clear layer. It may be necessary to add that neither of these two words is strictly definable, for in some cases, at least, hyaloplasm is not more rigid than the endoplasm, while in other cases it is. Strictness of definition can, of course, come only as investigation proceeds; and these words as well as the word endoplasm, should not be taken as defining the properties of the substances to which they refer, but only as labels.

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