Amoeba kerrii (n. sp.): Morphology, Cytology, and Life-History

ABSTRACT 1. An amoeba characteristically blackish when viewed under the low power of a Greenough binocular in reflected light was discovered and isolated from macerating water weeds found in fresh-water pools on the shore near the Marine Biological Station of Keppel. 2. A study of its morphology revealed its relationship to Schaeffer’s genus Metachaos. For reasons given above, the name Amoeba has been retained for the genus and the specific name kerrii has been given in honour of Sir John Graham Kerr. 3. The life-history has been worked out by means of pure-line cultures. 4. The cyst measures about 9µ in diameter. The newly hatched amoebulae grow slowly and develop eventually into young adults which, because of the small size of their crystals and nutritive spheres, are much less dusky than the mature individuals first discovered. An average adult size in creeping is 504 by 576µ. 5. The nucleus, which divides by mitosis, has the same general build as that of A. discoides, A. proteus Y, A. lescherae. Immediately under the nuclear membrane is an achromatic network containing chromatin blocks and connected with a more or less centrally placed karyosome, the whole immersed in-nuclear sap. The nucleus assumes varying shapes as it is rolled about by the streaming endoplasm. 6. Morula-like spheres (= the fission-spheres) give rise to two daughter amoebae by cleavage along a meridional central plane. Fission is confined to young adults. 7. A fission cycle is succeeded by a reproductive cycle. Any mature amoeba can give rise to encysted young which are formed by the action of chromidia escaping from the nucleus. The cyst-wall is single. Hundreds of encysted amoebulae may be formed from one mature amoeba. No sexual stages occur.