506 P. W. CLAASSEN 
produce a drier situation in which to cast off its coat. This variation 
indicates that A. obliqua is better adapted than WN. oblonga to live in 
moist or wet situations. A comparison of the tracheal systems of the 
two larvae shows this yet more clearly. A. obliqua has the spiracles 
of the eighth abdominal segment located on the dorsal surface and 
they are more than twice the size of the other spiracles of the body. 
Directly attached to these spiracles are the two longitudinal tracheal © 
trunks of the body. Segment 9 of the abdomen is flattened dorsally so 
as to be only half as thick dorso-ventrally as the other abdominal segments, 
thus making room for the large spiracles on the eighth segment. ‘This 
allows the body of the larva to be almost entirely submerged in the water, 
for as long as these spiracles remain above the surface it suffers no harm. 
The tracheal system of N. oblonga has not undergone any such modifica- 
tions, however. The spiracles on- its eighth abdominal segment are 
located in the natural position and are the same size as the other abdominal 
spiracles. Consequently the larva is likely to suffer harm if much water 
gathers in the burrow, as often occurs in wet situations. The larvae 
of A. obliqua remain in the leaf of Typha only through the first instar, 
while the larvae of N. oblonga often remain in the leaf through the second 
and even the third instar. The nature of their mining habits may have 
much to do with the difference. A. obliqua does not destroy the longi- 
tudinal partitions of the cat-tail leaf, and consequently must get out 
after its first molt on account of its increased size in the second stage. 
N. oblonga, however, cuts through the partitions in any direction and so 
is able to remain in the leaf for a longer period. After leaving the leaf, 
both larvae become solitary borers in the stalks of cat-tail. 
INSECT INHABITANTS OF THE STALK OF TYPHA 
The msects which work in the stalks of the cat-tail include two species 
of the Lepidoptera, Arzama obliqua Walk. and Nonagria oblonga Grote, 
and the Coleoptera, Calendra pertinax Oliv. and Notaris puncticollis Lee. 
After the larvae of A. obliqua and N. oblonga leave the mines of the 
leaf, they become stem borers. Their methods of entering the stem are 
very similar. Both are frequently found feeding for a time behind the 
sheaths of the outer leaves of the plant. From the sheath they either 
bore directly into the stem or enter from between the leaves of the leaf 
bundle. Both work their way to the center of the plant and locate at 
