The term form is used by different people to mean different things and by the same person to mean different things on different occasions. The psychological problem of how animals and men perceive form requires a definition of what it is that is perceived. Experiments in the field of form-perception and constancy of shape can only be decisive if one experimenter knows what the other is talking about. In the vast majority of studies of form-perception it is artificial deposits of one or another sort on a paper surface. The theories of visual form, on the whole, have been based on evidence obtained with outline drawings. The reasons for supposing that the primary kind of form is a drawn form would make a long chapter in the history of scientific thought. Outline-forms and also pictorial-, plan-, perspective-, and nonsense-forms are representations which the perceiver takes to stand for realities.