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.
In my paper of 1942, I did not regard the corpus allatum of the adult fly as a part of the ringgland. This was unfortunate. The ring-gland of a newly emerged fly comprises the corpus allatum, the side lobes and the corpus cardiacum fused with the ganglion hypocerebrale. The side lobes, homologous with the ‘pericardial glands’ of lower insects (E. Thomsen, 1941), degenerate during the first three days of adult life, but the corpus allatum and the corpus cardiacum persist. So it is only in the newly hatched fly that one can actually speak of the ring-gland.
In the older experiments the transplantation of the corpora allata was performed by means of forceps, in the present experiments by means of the transplantation method of Ephrussi & Beadle, but in other experiments mentioned on p. 153 I tried both methods of transplantation with the same result. So the divergent results cannot be due to the difference in technique.
I had the pleasure of discussing this problem with Dr Wigglesworth, who has permitted me to state that he suggested the possibility that the corpus allatum might be stimulated to release its hormone by afferent fibres in the nervi oesophagi. This problem certainly deserves a special investigation.
