The colour change displayed by many species is initiated by hormones secreted by the pituitary gland.
ðə kˈʌlɚ tʃˈeɪndʒ dɪsplˈeɪd baɪ mˈɛni spˈiːsiːz ɪz ɪnˈɪʃɪˌeɪɾᵻd baɪ hˈoːɹmoʊnz sᵻkɹˈiːɾᵻd baɪ ðə pɪtˈuːətˌɛɹi ɡlˈænd.