Midrasz do Kapłańska 11:27

1) (Vayikra 11:26) "By (touching) every beast": to include the embryo, that ever min hechai from it confers tumah (i.e., if one cut a limb from it in the womb, it is tamei as ever min hechai.). (Vayikra 11:26): "They are tamei": We are hereby taught that they combine with each other (i.e., half a limb from one beast and half a limb from another combine to constitute the required amount for tumah). I might think that they (half-limbs of a beast also) combine with (half-limbs of) dead (men to constitute the required amount for ever min hechai tumah). It is, therefore, written (Vayikra 11:26): "They are tamei to you," (to exclude the above). I might think that they do not combine with (the tumah of) the dead, which is stringent (seven days), but they do combine with (the tumah of) neveiloth (of beasts), which is "light" (one day). It is, therefore, written (Vayikra 11:27): "They are tamei to you" (and not half a limb of ever min hechai in combination with half a limb of neveilah). (Vayikra 11:26): "Everyone who touches them shall be tamei": to include an unclean beast, its shechitah not freeing it (of neveilah tumah).

5) (Vayikra 11:27): "that walks upon its soles": This is the ape. "And all that walk": to include (in all of these laws of tumah, even though they have no hooves at all) the long-tailed ape, the porcupine, the adnei hasadeh, and the sea-dog. (Vayikra 11:27): "the animal": This is the clean animal. Whence do I derive (for inclusion in the laws of tumah) the unclean animal? From "which walk on four." "among all animals": to include the elephant (though it is "unique").

5) "and he who touches their carcass shall be tamei": Hillel says: Even if they are in the midst of the water. For I would say: Since (being connected to) the earth rescues (what is connected to it) from becoming tamei (viz. Vayikra 11:27) and the mikvah rescues what is tamei from their tumah, then just as the earth rescues the clean from becoming tamei, so the mikvah rescues the clean from becoming tamei. It is, therefore, written "and he who touches their carcass shall be unclean," even if they are in the midst of the water.