As Kṛṣṇa has got form, sac-cid-ānanda-vigraha (Bs. 5.1), similarly spirit soul, jīvātmā, being part and parcel of Kṛṣṇa, it has got form. That form is also described in the śāstra: keśāgra-śata-bhāgasya śatadhā kalpitasya ca, jīva bhāgo sa vijñeyaḥ (Śvetāśvatara Upaniṣad 5.9). A rough idea of the form of the living entity has been given in the Padma Purāṇa, that one ten-thousandth part of the tip of the hair. Now, perhaps we have no instrument how to measure one ten-thousandth part of the tip of the hair. But this is given there.
So anyway, because we get information from the Bhagavad-gītā that this body, material body is . . . is like a dress. Vāsāṁsi jīrṇāny yathā vihāya (BG 2.22). As we give up old dress, garment, similarly, when this body becomes useless, we give up this body and accept another, new body. Navāni ghṛṇāti. This is the transmigration of the soul. The soul is transmigrating from one body to another. That is a fact. But the gross . . . gross materialists, they cannot see the subtle body. They simply see the gross body. Therefore they say, "When this body is finished, this gross body's finished, everything is finished." No, that is not. Within the gross body, there is subtle body, made of mind, intelligence and ego.