NEUROSECRETION VI. A COMPARISON BETWEEN THE INTERCEREBRALIS-CARDIACUM-ALLATUM SYSTEM OF THE INSECTS AND THE HYPOTHALAMO-HYPOPHYSEAL SYSTEM OF THE VERTEBRATES

Abstract

The hypothalamo-hypophyseal system in vertebrates is in many respects similar to the intercerebralis-cardiacum-allatum system in insects. (1) In vertebrates the hypothalamic nuclei innervating the pars nervosa of the pituitary gland contain secreting nerve cells. In a number of species colloid droplets can be traced along the axons from the neurosecretory cells of the hypothalamus to the hypophysis. (2) In insects the pars intercerebralis of the protocerebrum contains neurosecretory cells. A bundle (nervus corporis cardiaci) innervating the corpus cardiacum and probably also the corpus allatum originates in the pars intercerebralis. In Leucophaea (Orthoptera) as in the vertebrates, colloid can be traced from the secreting nerve cells of the pars intercerebralis to the corpora cardiaca all along the nervus corporis cardiaci. (3) On the basis of these morphological relationships the hypothalamic nuclei (nucleus preopticus and its homologues) and the pars nervosa of the hypophysis appear as one closely interconnected system. Likewise the pars intercerebralis and the corpus cardiacum of insects may be viewed as one neuro-endocrine complex rather than as two separate sources of hormones. In this way certain seemingly inconsistent data concerning the endocrine control of development in insects can be better understood (see p. 244).