I2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
episterna until they meet along the midline of the back in front of the 
wings, and the corresponding downward extension of the metathoracic 
epimera on the ventral surface behind the legs. These features of the 
thorax evidently have no particular functional significance for the 
larva, since the larva uses its legs in the ordinary manner for locomo- 
tion, and its wings are entirely passive rudiments of the future organs 
of flight. On the other hand, the thoracic structure is clearly a func- 
tional adaptation for the benefit of the adult; it must have been early 
impressed upon the larva, and retained by the larva because it had no 
disadvantage for the larval activities’ (Snodgrass, 1954). Sargent 
(1937), by puncture-scarring the larval cuticle, has shown that the 
dorsal extension of the mesothoracic episterna takes place by marginal 
growth, while the metathoracic epimera increase both by general ex- 
pansion and by growth of the ventral margins. The postcoxal plate 
of the metasternum, according to Sargent, moves bodily backward 
from the legs as the epimeral plates intervene. 
THORACIC TERGA 
PRONOTUM: The prothoracic tergum (fig. 14) consists of a single 
large sclerite, the pronotum (n,), which is roughly transversely rec- 
tangular in shape. The anterodorsal angles are produced as hemi- 
spherical lobes each of which bears numerous long setae and short 
spines. The disc or dorsal surface of the pronotum consists of two 
oblong glabrous areas which are bounded anteriorly and posteriorly by 
bands of minute inconspicuous setae and separated by a median longi- 
tudinal spiniferous band which is enlarged at either end. A conspicu- 
ous pit close to the spiniferous anterior margin marks the position of 
the prothoracic tergal apophysis (ta,) which gives attachment to the 
dorsal longitudinal muscles (Asahina, 1954). 
MESONOTUM: The mesothoracic tergum (fig. 14) is transversely 
compressed as a result of the upward extension of the pleural sclerites. 
The mesonotum proper is demarked into four main regions: acro- 
tergite, prescutum, scutum, and scutellum. A portion of the dorsal 
surface of the intersegmental membrane, lying between the meso- 
thoracic spiracles, has become secondarily sclerotized forming a plate 
which narrows anteriorly and is roughly trapezoidal in shape. 
The acrotergite (atg) is the anteriormost mesotergal sclerite. It is 
secondarily divided into two triangular plates with posteriorly directed 
apices. It is extremely reduced and separated from the prescutum 
by membrane. 
The prescutum (psc2) is a much-reduced, longitudinally elongate, 
protuberant sclerite between the dorsally extended portions of the 
