580 Cuin PING 
longitudinally along the dorsum of the second and third segments, and 
through this dorsal opening emerges the head of the larva of the next 
instar. The rent here may become much enlarged, extending backward 
as far as the sixth segment, while the larva is struggling for liberation. 
It seems that the larva does not encounter much difficulty in slipping out 
of the old skin. Because of its cylindrical body and short prolegs its 
escape is easy. Sometimes, however, the last pair of prolegs causes a 
great deal of trouble. These prolegs are often caught on the cast skin 
with their claws. After a struggle, lasting sometimes for half an hour, 
when the caudal processes have been pulied out, these remain still entangled 
with the cast skin. The larva, as it has sometimes been observed, twisting 
and bending its body, uses its mouth parts to bite this off. In the exuviae 
are found the entire cephalopharyngeal skeleton, part of the alimentary 
tube, and the tracheal trunks from out the caudal processes. 
The writer did not observe the second molting. A premature molting 
may be caused by subjecting the larva to certain abnormal conditions, 
as once it was done by accidentally dropping larvae in kerosene. Such 
a molt, however, is quite different from an ordinary ecdysis; it consists 
of nothing more than the primary cuticula, and the structures that are 
east off sometimes with the ecdysis are not to be found in it. 
Instars 
The first instar— The newly hatched larva measures from 1 to 1.5 
millimeters in length. The body segments are very distinct but the 
caudal processes are just budding out. At their blunt end are chiefly 
visible the tracheal terminals. These terminals are much simpler than 
those found in a grown larva, each having an opening, laterad to which 
are two roughly outlined bullae. Of the anterior spiracular processes 
there is not a trace to be recognized during this stage. The cephalo- 
pharyngeal skeleton is delicate and slender in shape, consisting, at the 
anterior end, of a single piece of U-shaped mandible sclerite and, follow- 
ing this, a pair of H-shaped structures, representing the hypostomal 
sclerites in front and the lateral pharyngeal plates posteriorly. The 
mandible sclerite and the rest of the cephalopharyngeal skeleton are apart 
from each other, but they are connected and articulated with each other 
by muscles. The alimentary canal is a more or less straight tube and 
