2 
Psyche 
[March- June 
Observations on Larvae 
Since almost the entire larval life is spent in the uterus of the 
female ked, the young larva can be obtained only by dissection 
or in serial sections of the parent fly. All larval tissues retain 
many embryonic characteristics. According to Pratt (1901, 
p. 261) the glands (which he refers to throughout as ganglia 
allata, following Heymons, 1895) arise from the headfold as a 
pair of spherical bodies, probably from the lateral ectoderm, 
rather than from the ventral ectoderm as in most other insects. 
This is not surprising, however, in view of the great modifica- 
tion in the development of other organs of these Diptera when 
compared with more generalized insects. 
The number of larval instars has not been determined. 
Larvae are therefore classified according to their size. Three 
stages are described in detail. The youngest larva studied in 
the present series was about 0.8 mm. in length. This stage is 
only slightly more advanced than Pratt’s (1901) Figs. 43 and 
44, and already the tissue forming the corpora allata can be 
clearly distinguished from the brain tissue. The unusually large 
size of the cells is clearly seen in Pratt’s illustrations. Cytologi- 
cally the corpus allatum cells are very characteristic, presenting 
a considerably larger amount of even, deeply staining, basophilic 
cytoplasm than is found in any other cells of the embryo. 
In a larva approximately 2 mm. in length (Fig. 1) the gland 
has increased in cell size and in cell number, but not to such an 
extent that each cell could have divided once. The cytoplasm is 
even more basophilic than that of the younger larva, and the 
cells appear to be in a state of secretory activity. In five mature 
larvae studied corpora allata are greatly enlarged (Fig. 2). It 
is to be noted that the gland is a paired structure and thus 
differs fundamentally from the median corpus allatum of the 
Brachycera. Moreover, the cells composing it are large and 
conspicuous and show cytological indications of considerable 
activity, while the corpus allatum in the larva of Brachycera 
shows no cytological evidence of secretory changes. The corpus 
cardiacum, however, is inconspicuous in the larva of Melo- 
phagus , again in striking contrast to the situation in the 
Brachycera. 
Each corpus allatum of a mature larva measures approxi- 
mately 150 microns x 125 microns, and extends from the median 
region laterally between the imaginal discs and the dorsal ex- 
