AMEBOID MOVEMENT 19 



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 po- 

 sition 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 com- 

 plicated process than in almost any other ameba, excepting the 

 large species Amoeba carolinensis 1 discovered by Wilson ('oo). 

 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 pseudo- 

 pods 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 for- 

 mation at the anterior ends of pseudopods only, we find this pro- 

 cess 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 sympa- 



1 Wilson ('oo) describes it as Pelomyxa, but it has much closer affin- 

 ities with Amoeba. It is in fact perhaps the closest relative of Amoeba 

 proteus. Ectoplasm formation, and especially the formation of ectoplasmic 

 ridges in carolinensis, is exactly like that in proteus. 



