In this note, we consider the control system of a biological system. Further, we point out the existence of the problem of indivisibility in the control system. To understand the principle of mobile adaptability embedded in the control system, we must solve the problem of indivisibility. To solve this problem, we propose the concept of an implicit control law. In addition to this proposal, we consider the usual explicit control law. Next, we demonstrate an example of the implicit control law embedded in the problem of a passive dynamic walking system. Finally, we state that the intelligence of the biological system must be constructed using both the explicit and the implicit control laws.