[Illustration: Figure 11. _A_, _Amoeba_ proteus in locomotion. Note especially the longitudinal ridges. _a_^{1}, equatorial view of the _discoid_ nucleus. _a_^{2}, a polar view of the nucleus. _a_^{3}, equatorial view of a folded or crushed nucleus frequently found in large individuals. _a_^{4}, shape of crystals found in this species._B_, _Amoeba discoides_ in locomotion. _b_^{1}, _b_^{2}, equatorial and polar views of the _discoid_ nucleus. _b_^{3}, shape of the crystals found in the ameba. _C_, _Amoeba dubia_ in locomotion. _c_^{1} and _c_^{2}, equatorial and polar views of the _ovoid_ nucleus. _c_^{3}-_c_^{10}, 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; _a_^{1}, 46 × 12; _b_^{1}, 40 × 18; _c_^{1}, 40 × 32; _a_^{4}, maximum, 4.5; _b_^{3}, maximum, 2.5; _c_^{3}-_c_^{10}, 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 | _Amoeba | _Amoeba | _Amoeba Characteristics | discoides_ | proteus_ | dubia_ ------------------+-----------------+------------------+------------------ Size in locomotion|450 microns |600 microns |400 microns Pseudopods |cylindrical |dorso-ventrally |dorso-ventrally | | flattened | flattened |smooth ectoplasm |folded ectoplasm |smooth ectoplasm |“main” pseudopod |“main” pseudopod |no “main” pseudopod | present | present | |cross section |cross section an |cross section | circular | irregular oval | oval |average number |average number |average number | in locomotion, | in locomotion, | in locomotion, | three | five | twelve Crystals |very numerous |less than in |relatively few | | _discoides_ | |all uniform |all uniform |at least four |truncated | truncated | varieties present; |bi-pyramids | bi-pyramids; | few perfect | | rarely a | crystals | | few flat plates | |maximum size |maximum size | maximum size | 2.5µ 4.5µ 10µ, 12µ, 30µ Fission |slower than |average 1 division| faster than _proteus_ | _proteus_ | in 48 hours at | | | 20° C. | Maximum time | | |