[en] The mechanical models of the bi-local fields and the string models are discussed in the formal point of view. Since the formulation of the extended particle pictures has no unique way, there are various formulations even in the simplest bilocal models. We confine ourselves mainly in the formulations by following which the interactions have been investigated. The scattering amplitudes and the form factors are discussed qualitatively. Some comments on the subsidiary conditions suppressing the relative time freedom are given by following Dirac's formalism. A short discussion of the bi-local model with spin is also shown by introducing Grassmann variables as classical variables corresponding to spin freedom. As to the string model, we have discussed various interesting but unsolved problems; namely, the electromagnetic interactions, the string with massive ends, the spinning string and so on. We have proposed tentative prescriptions for treating some of these problems. We also discuss the different point of view concerning the string model. That is, we show that the difference equation furnishes us the same result as that given by the string model. (author)