Functional Significance Of The Neurosecretory Brain Cells And The Corpus Cardiacum In The Female Blow-Fly, Calliphora Erythrocephala Meig

Abstract

ABSTRACT The neurosecretory cells of the protocerebrum of the adult female Calliphora erythrocephala comprise two medial groups, each consisting of about eight cells, and two lateral groups, each consisting of three cells. Since the corpus allatum is probably innervated from the neurosecretory cells of the brain, it was originally supposed that the function of the neurosecretory cells was the activation of the corpus allatum. Experiments were therefore carried out to discover whether extirpation of the neurosecretory cells had an effect like that of allatectomy. The excision of the two medial groups of neurosecretory cells (m.n.c.) had an effect on the ovaries which was clearly different from that of allatectomy. From this fact it is inferred that the effect of the m.n.c. on ovarian development is not solely through the corpus allatum, but that the m.n.c. must affect some other physiological process vital to egg development. The fat-body of females deprived of m.n.c. and of allatectomized females contained much glycogen, whereas the content of fat in the fat-body of females deprived of m.n.c. was generally smaller than in allatectomized females. The accessory glands of females deprived of m.n.c. were of nearly the same length as those of allatectomized females. The corpora allata of the females deprived of m.n.c. were definitely smaller than the corpora allata of the operated controls; this fact supports the assumption of an activation of the corpus allatum by the m.n.c. Corpora allata of 7 days old females, when implanted into females deprived of m.n.c., had a slight effect on the growth of the ovaries, but were not able to bring about the development of ripe eggs. M.n.c. from 7 days old females when grafted into females deprived of m.n.c. had a definite effect on the growth of the egg-chambers; this fact shows that the m.n.c. act on the ovaries by means of a hormone which they produce. The lateral neurosecretory cells probably have a slight influence on egg development. Flies are able to develop eggs in the absence of the corpus cardiacum; this shows that the neurosecretory cells and the corpus allatum alone are able to further the development of the ovaries. The cutting of the two nervi oesophagi resulted in a retardation of ovarian development and in a hypertrophy of the fat-body. The corpus cardiacum was found to have a similar effect on the growth of the ovaries as the m.n.c., but must be activated by the m.n.c. in order to exert its effect. The influence of the corpus cardiacum on egg development is due to a hormone released by this organ. The stimulation of the corpus cardiacum-allatum system by the neurosecretory cells is partly hormonal. Thus in Calliphora the m.n.c. must be regarded as the over-all controlling centre of the endocrine system. It is suggested that the problem of the function of the m.n.c. and the corpus cardiacum in the adult Calliphora may be regarded as a problem of growth. The growth of the egg-chambers and of the accessory glands in the adult fly was studied. (The growth of the corpus allatum has previously been investigated by the author). The growth of the same organs in flies fed sugar and water, but no meat (‘sugar flies’), was compared with the growth of the organs of flies fed sugar, water and meat. The slight growth of the organs of the ‘sugar flies’ was ascribed to the protein content of the larval fat-body, and it was suggested that the breaking down of this fat-body is regulated by the side lobes of the ring-gland. As the egg-chambers, the corpus allatum and the accessory glands of the flies deprived of m.n.c. were of nearly the same size as the organs of the ‘sugar flies’, a working hypothesis is put forward that the m.n.c. and the corpus cardiacum exert a profound influence on the protein metabolism of the fly. There is some evidence that it is the synthesis of protein which is concerned.