36 AMEBOID MOVEMENT 



and withdrawal, in the manner of their withdrawal, in their dis- 

 position with respect to geometrical pattern, in the charac- 

 ter of the bases of the pseudopods, in the form of the free ends, 

 and so on. Many of these characteristics are still further analyz- 

 able into numerous other and more detailed characters. And 

 what is true of the static pseudopods is likewise true of the 

 transitional and the directive. Pseudopod formation is however 

 only a small part of the activity of an ameba. The formation of 

 uroidal projections, of vacuoles of various sorts, of crystals, and 

 so on, are some other general activities that are fully as subject 

 to specific variation as pseudopod formation. Again in behavior 

 to food and various other stimuli, in resistance to various factors 

 in the environment, in reproductive processes, and so forth, there 

 is found similar specific peculiarity. In fact, one looks in vain 

 for similarity, between any two species of amebas except in their 

 most generalized characters. From my own experience in ex- 

 tended observation of several dozen species, which included a 

 large number of characters, as pointed out above, I have not 

 found two species of which I can confidently assert that any 

 particular character defined as accurately as possible was present 

 in both. In different words, my experience indicates that no two 

 species are alike in any respect whatsoever. Each species appears 

 unique from every point of view and in the smallest definable 

 detail. The concept of specificity therefore is much more fun- 

 damental in amebas than has been believed to be the case hith- 

 erto (cf. Calkins, '12). The intimate structure of amebas is in- 

 deed similar to that of higher animals where the precipitin reac- 

 tions (Richet, '02, '12; Reichert and Brown, '09; Dale, '12; Nut- 

 tal, '04; also Todd, '14) have indicated that the various albumins 

 are of specific structure and reaction. 



As an example of these specific differences, reference may be 

 made to the three species, protus, dubia and discoides, which 

 have been referred to in the past, almost without exception, by 

 the most experienced teachers of biology, as being one species : 

 proteus. Some investigators of ameboid phenomena have like- 

 wise confused these different amebas. Below is given a list of 

 some of the most striking characteristics of these three amebas. 

 This list is of course very sketchy. If the nuclear division 



