Figure 10. Graph representing the relation of firmness and thickness of the ectoplasm with the number and character of the pseudopods in different species of amebas. a, the average maximum number of pseudopods directing locomotion in the different species of amebas. b, the number of transitional pseudopods. c, the number of static pseudopods. d, the estimated degree of firmness and thickness of the ectoplasm of the various species of amebas, grading that of limicola as 1 and that of verrucosa as 6.
That the number and character of pseudopods formed depends in large part upon the firmness and thickness of the ectoplasm was said advisedly. For observations indicate that there are other factors which influence the character of pseudopods besides those which also control the formation of ectoplasm. These other factors indicate their presence readily in the details of structure of the pseudopods. Thus the number of directive, transitional or static pseudopods may be the same in two particular species, yet in their intimate structure and appearance they are always found to differ. In bigemma, bilzi and radiosa, for example, the number of static pseudopods when formed is about the same in the three species, but the similarity ends there. For these species differ in the frequency with which pseudopods are formed, in their persistence when once formed, in the ratio of length to average diameter, in the general shape, in the frequency with which straight pseudopods are formed, in the speed of their formation and withdrawal, in the manner of their withdrawal, in their disposition with respect to geometrical pattern, in the character of the bases of the pseudopods, in the form of the free ends, and so on. Many of these characteristics are still further analyzable 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 extended 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 fundamental in amebas than has been believed to be the case hitherto (cf. Calkins, ’12). The intimate structure of amebas is indeed similar to that of higher animals where the precipitin reactions (Richet, ’02, ’12; Reichert and Brown, ’09; Dale, ’12; Nuttal, ’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 likewise 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 phenomena, for example, were well known, which they are not, those character differences alone would doubtless make a list several times as long as this one. Compare with [Figure 11.]
Figure 11. A, Amoeba proteus in locomotion. Note especially the longitudinal ridges. a1, equatorial view of the discoid nucleus. a2, a polar view of the nucleus. a3, equatorial view of a folded or crushed nucleus frequently found in large individuals. a4, shape of crystals found in this species.B, Amoeba discoides in locomotion. b1, b2, equatorial and polar views of the discoid nucleus. b3, shape of the crystals found in the ameba. C, Amoeba dubia in locomotion. c1 and c2, equatorial and polar views of the ovoid nucleus. c3-c10, shapes of crystals found in dubia. In these drawings only such characters as are of special interest for the purpose of this work are emphasized. Dimensions in microns: A, 600; B, 450; C, 400; a1, 46 × 12; b1, 40 × 18; c1, 40 × 32; a4, maximum, 4.5; b3, maximum, 2.5; c3-c10, maxima, 10 to 30.
This fundamental uniqueness of all the characters of the various species of amebas naturally gives rise to the question as to what is the cause of this condition of affairs. Why and how
| Characteristics | Amoeba discoides | Amoeba proteus | Amoeba dubia |
| Size in locomotion | 450 microns | 600 microns | 400 microns |
| Pseudopods | cylindrical smooth ectoplasm “main” pseudopod present cross section circular average number in locomotion, three | dorso-ventrally flattened ectoplasm “main” pseudopod present cross section an irregular oval average number in locomotion, five | dorso-ventrally flattened smooth ectoplasm no “main” pseudopod cross section oval average number in locomotion, twelve |
| Crystals | very numerous all uniform truncated bi-pyramids maximum size 2.5µ | less than in discoides all uniform truncated bi-pyramids; rarely a few flat plates maximum size 4.5µ | relatively few at least four varieties present; few perfect crystals maximum size 10µ, 12µ, 30µ |
| Fission | slower than proteus | average 1 division in 48 hours at 20° C. | faster than proteus |
| Maximum time between divisions | 20 days | 8 days | 6 days |
| Multinuclearity | binucleate occasionally | binucleate frequent; tetranucleate occasional | binucleate very rarely |
| Nucleus, shape | biconcave disc, never folded | biconcave disc, frequently folded | ovoidal |
| size | 40µ × 18µ | 46µ × 12µ | 40µ × 32µ |
| General resistance to same conditions | slight | very great | greater than discoides |
| Surface of posterior end | free from debris | free from debris | carries debris |
| Effect of mechanical stimuli | slightly responsive | responsive | very responsive |
| Food cups | small | large | often enormous |
| Reaction to carmine | readily eaten; rejected in a few minutes | readily eaten; rejected in a few minutes | eaten only occasionally; often retained for hrs. |
| Distribution | sporadic, small numbers | very common | sporadic, frequently in large numbers |
are the different species of amebas so absolutely different, even to the smallest detail? Why are the apparent resemblances and similarities of their more generalized kinetic characters, such as the formation of pseudopods, of ectoplasm, of crystals, of contractile vacuoles, the general character of endoplasmic streaming, the formation of ectoplasmic ridges, and so forth, found, upon analysis, to resolve themselves into a large number of details which differ more strikingly, the corresponding characters of one from those of the other, than do the generalized characters of which they are composed?