(1) An exceedingly minute body that, according to the views of development held by some medical scientists of the 16th and 17th centuries, was contained in a sperm or an oocyte. From this preformed but infinitely small structure, the human body was thought to be developed.preformation theory, animalcule. (2) The distorted figure of a human superimposed on an illustration of the surface of the brain; used to demonstrate those portions of the body supplied by the various motor and sensory cortical regions. [L. dim. of homo, man]