position and the world of important visual objects in the case of
those animals which are immersed in a free medium; and in the
organization of the fish and the bird, therefore, one should not
expect the development of such free sensory reflexes of the eye in
independence of head movements as we know to be characteristic of the
higher land vertebrates. In both of the former types the eye is fixed
in its socket, movements of the whole head or body becoming the
mechanism of adjustment to new objects of observation. In the
adjustment of the human eye the reflex determination through sensory
stimuli is so facile as to counteract all ordinary movements of the
head, the gaze remaining fixed upon the object through a series of
minute and rapidly repeated sensory reflexes. When the eyes are closed
and no such visual stimuli are presented, similar reflexes take place
in response to the movements of the head, mediated possibly by
sensations connected with changes in position of the planes of the
semicircular canals.


VII.


If eye-strain be a significant element in the process of determining
the subjective horizon, the induction of a new center of muscular
equilibrium by training the eyes to become accustomed to unusual
positions should result in the appearance of characteristic errors of
displacement. In the case of two observers, _A_ and _H_, the eyes were
sharply raised or lowered for eight seconds before giving judgment as
to the position of the illuminated spot, which was exposed at the
moment when the eyes were brought back to the primary position. The
effect of any such vertical rotation is to stretch the antagonistic