Comparative endocrinology is concerned with the many complexities of vertebrate and invertebrate endocrine systems at the sub-molecular, molecular, cellular and organismal levels of analysis. It is an interdisciplinary knowledge in the fields of biology and medicine concerned with the morphological and functional aspects. Comparative endocrinology is concerned with the many complexities of vertebrate and invertebrate endocrine systems at the sub-molecular, molecular, cellular and organismal levels of analysis. It is an interdisciplinary knowledge in the fields of biology and medicine concerned with the morphological and functional aspects.