The locomotion of Mnemiopsis leidyi, as it moves along with its oral end forward near the surface of the water, serves to demonstrate that this animal possesses a definite polarity. The forward movement is a continuous reaction and is interrupted only when the animal bumps into some definite obstruction. Even this interruption is very brief, for immediately afterward the animal resumes its oral direction of movement. This locomotion of Mnemiopsis demonstrates a definite polarity within the rows of plates since the beating of the plates causes the animal to move, and this in turn indicates the presence of some sort of dominance. The proof of this dominance, with its location and character, has been reported by Child (1917, 1933) and Coonfield (1934). The conclusion reached thus far is to the effect that the apical organ, or region, exerts a dominance over the other parts of the body. In support of this conclusion, I offer further experimental evidence which is listed and discussed according to the following five headings: (1) Swimming-plate movement, (2) feeding reactions, (3) reversing parts of plate-rows by grafting, (4) reversing the midbody section by grafting, (5) transplanting the apical organ.