this is called SPHERICAL ABERRATION; at the same time the coloured rays are separated by the prismatic action of the lens and likewise brought to a focus at different distances — this is CHROMATIC ABERRATION.

ABNORMAL. — Contrary to the general rule.

ABORTED. — An organ is said to be aborted, when its development has been arrested at a very early stage.

ALBINISM. — Albinos are animals in which the usual colouring matters characteristic of the species have not been produced in the skin and its appendages. Albinism is the state of being an albino.

ALGAE. — A class of plants including the ordinary sea-weeds and the filamentous fresh-water weeds.

ALTERNATION OF GENERATIONS. —