1924 ] The Biology of Trichopoda pennipes Fab. 63 
apparent in Tachinidse and Dexiidse is conditioned by the 
presence of the posttergite (pt^), which, as a glance at the figure 
will show, lies just below the scutellum. An examination of 
figures 38, 39, 40 and 41 of Young bears out this point. 
The pleural region of the mesothorax is pollinose gray in 
color, and is much distorted. The pleural suture, which in 
generalized insects runs a nearly straight course from the coxal 
cavity to the wing base, thus dividing the pleuron into an an- 
terior episternum and a posterior epimeron, is here bent twice 
at right angles, so that while the two ends are nearly vertical, 
the middle is horizontal. In addition a portion of the anepister- 
num (aes^) has been split off from the rest by a secondary in- 
vasion of membrane, and has become closely associated with 
the anepimeron or pteropleurite (ptp.^) The katepisternum has 
fused with the sternum to form the sternopleurite (stp^). It is 
the enlargement of this sclerite which has evidently caused the 
bending of the pleural suture, and has crowded the meropleurite 
(mep2), which is composed of katepimeron plus meron, back 
against the pleuron of the metathorax. 
The numerous small plates which lie in the membrane sur- 
rounding the base of the wing are very difficult to see, but are 
easily identified with those sclerites outlined by Crampton (1914) 
in his ground plan of a typical thoracic segment in winged insects. 
The tegula (tg) lies in the angle between the scutum and the 
anepisternum. The notale (n) is a detached portion of the 
scutum lying just above the base of the wing. The basalar 
plates are two in number, the anterior one (aba) not demarked 
from the posterior portion of the anepisternum, the posterior 
one (pba) very small and lying between it and the pleural wing 
process (wp). The subalar plates are two in number, the an- 
terior one (asa) lying behind the wing process and above the 
pteropleurite, the posterior one (psa) which is much smaller 
lying just below a posterior lateral process of the scutum. These 
basalar and subalar plates are the pre and post paraptera of 
Snodgrass (l909a). 
The tergum of the metathorax, or the metanotum (m) is 
reduced to a narrow band connecting the halteres (ha), and 
visible only at the sides where it is produced to form points of 
