External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time.
ɛkstˈɜːnəl ɡˈɪlz duːnˌɑːt ɹᵻtˈɜːn ɪn sˈʌbsᵻkwənt əkwˈæɾɪk fˈeɪzᵻz bɪkˈʌz ðiːz ɑːɹ kəmplˈiːtli ɐbsˈoːɹbd əpˌɑːn lˈiːvɪŋ ðə wˈɔːɾɚ fɚðə fˈɜːst tˈaɪm.