1943] 
Corpus Allatum of Sheep Ked 
5 
pupa and adult. Cytologically the cells of the adult Melophagus 
behave similarly to those of Lucilia. Neither show visible evi- 
dence of secretory activity, though in Lucilia , at least, marked 
physiological effects of the ring gland have been demonstrated 
by experiments. 
The changes undergone by the cells of the corpora allata 
which have been described above can be tabulated as fol- 
lows: 
TABLE 1 
Changes in the cells of the corpora allata of Melophagus during 
DEVELOPMENT 
Approximate number Average size in microns 
of cells in each 
Stage corpus allatum Nucleus Cell 
2 mm. larva 250 6.9 11 x 15 
mature larva 300 11.0 17 x 19 
white pupa , 8.7 14 x 15 
adult 100 7.3 12.5 x 13 
The reduction in the corpus cardiacum during late larval 
and pupal development in Melophagus is in general similar to 
the reduction found in Lucilia , but this gland is never very con- 
spicuous in Melophagus and practically absent in the adult. 
It is perhaps not surprising to find such differences in the 
behavior of the incretory organs of Melophagus and Lucilia 
when one considers the great differences in their reproductive 
processes, but the fact that the corpus allatum is a single median 
organ in Lucilia and paired in Melophagus , as in Nematocera 
and the majority of insects, is evidence that there are some 
fundamental differences between the Hippoboscoidea and 
Muscoidea. 
Summary and Conclusions 
The incretory organs associated with the stomodeal nervous 
system of Melophagus exhibit the following characteristics: 
1. There is a pair of corpora allata, as in Nematocera and 
the majority of other insects, rather than a median unpaired 
structure as in the higher Diptera. The cells and nuclei are 
extremely large in the larva, and so differ in this also from those 
of the corpora allata of the Brachycera. 
