In attempting to explain the characteristic nature of the path of the ameba, one’s attention centers first, perhaps, upon its orderliness; a result undoubtedly of the general impression propagated through hastily written textbooks and general papers, that an ameba’s whole life is a direct response to its environment. As the recorded facts of the life of this organism are accumulating, it is coming to be seen that the ameba possesses all the fundamental attributes of animals generally, in addition to many special ones. So that as a matter of fact, if the ameba did not show some character and orderliness in its locomotion, then for the first time should we be especially interested in what would have to be regarded as a very striking and exceptional characteristic. For it is very well known, and it is generally recognized by everybody, that moving organisms usually move in an orderly manner; it is recognized that organisms tend to move in straight paths excepting where interrupted by the action of some special stimulus. When an organism changes its direction of motion frequently and abruptly, we call it erratic. The mad dashings-about of the hunter-cilitae _Didinium_ and the unceasing gyrations of the whirligig beetle excite one’s curiosity because these organisms do not move as other organisms do; they contradict our expectation of movement in a straight line. But why should organisms generally tend to move in straight paths? This fundamentally important question has received almost no attention, excepting that rapidly moving animals like birds, flying insects, fishes and other rapidly swimming animals of various kinds and rapidly running animals tend to move in straight paths because of the physical inertia of the mass of the organism. It is easier for a rapidly moving organism to move in a straight line than to change its direction of movement frequently and abruptly. The ameba however is a very slow moving animal, as animals go, for it (_proteus_) moves only about 600 microns per minute. Under the microscope, however, which magnifies speed as well as size, the endoplasmic particles rush along rapidly enough to suggest that even here mere physical inertia might be a determining factor in the path of the ameba, which for considerable segments is often very nearly straight. Such suspicion is not justified, however, for the viscosity of the endoplasm taken in connection with the heterogeneous composition of the ameba, makes it improbable that mere physical inertia can affect the path of the ameba.[5] It is not even necessary that movement of the endoplasmic stream be interrupted in order that a straight path may be maintained. An ameba may stop movement for a minute or more and then be much more apt to resume movement in the original direction than in any other. This is brought out by the following series of experiments.