4 
Psyche 
[March- June 
of pupal development, they have assumed the form found in the 
adult. The glands have moved posteriorly, and come to lie, as 
they do in all adult Diptera, immediately in front of the 
proventriculus. 
The Adult. No differences have been found in the corpora 
allata of male (Fig. 3) and female (Fig. 4) Melophagus, nor in 
female Melophagus with or without larvae. The glands are 
ovoid, measuring approximately 75 microns x 60 microns. Each 
contains approximately twenty cells in cross section in the 
region of greatest diameter, the cells having approximate dimen- 
sions of 12 microns x 13 microns. The two glands lie one on 
each side of the dorsal aorta (Figs. 5 and 6). Ventral to them 
are the convolutions of the salivary glands, and immediately 
above them there are conspicuous tracheal trunks, which arise 
from the mesothoraoic spiracles. Immediately above the aorta 
there are numbers of large pericardial cells which are frequently 
multinucleate, and possess a coarsely reticulated cytoplasm. 
The cytoplasm of the cells of the corpora allata is sparse in 
comparison with that of the previous stages, and contains few 
or no vacuoles. The diameter of the nuclei is approximately 
7.3 microns. Their volume is thus approximately 25 per cent 
that of the nuclei of the mature larvae. The single large 
nucleoli are almost always eccentric. The cells are well inner- 
vated by nerve fibers arising from the region of the corpus 
cardiacum. Almost all traces of the secretory elements of the 
last mentioned gland have disappeared, but there remain a 
number of nerve cell bodies representing the hypocerebral 
ganglion. These are loosely arranged, and do not form a com- 
pact gland-like structure as is found in Lucilia. A second cell 
type represented by small cells scattered among the nerve cell 
bodies is probably connective tissue and supporting cells. The 
gross arrangement of the incretory organs is most clearly seen 
in Fig. 6. 
The most striking point of the observations reported above is 
the fact that the changes undergone by the corpora allata of 
Melophagus are so different from those occurring in Lucilia 
sericata as described by Day (1943). Whereas in the latter, 
the corpus allatum is very inconspicuous in the larva, and its 
cells reproduce by mitosis during the pupal period, in Melo- 
phagus the corpora allata reach their maximum size during 
late larval development, and are considerably reduced in both 
