TypHa Insects: THEIR EcoLoGicAL RELATIONSHIPS 473 
Usually only one egg mass occurs on the same leaf, but sometimes two, 
and in one instance three, masses were found on a single leaf. It is not 
uncommon to find two or three leaves of the same plant with an egg mass 
on each of them. 
In the spring of 1918, careful observations were made for the appearance 
of the adults or the egg masses on the plants. In the laboratory, where 
moths had been bred, they failed to mate or to deposit eggs in the char- 
acteristic manner. A few females did lay infertile eggs on the stems and 
leaves of Typha. Egg masses were first noticed in the field on May 26. 
After this date new egg masses were constantly found until June 8. The 
height of egg-laying was between May.26 and June 2. At the McLean 
Bogs the egg masses appeared about six days later than those at the 
places around Ithaca. 
The larva=— On turning the egg mass over, after the larvae have 
hatched, the empty egg shells are disclosed. The hatching process does 
not disturb the egg mass in the least. Without devouring the egg shell, 
the embryo breaks through it and bores directly into the leaf of the cat-tail, 
where it works as a leaf miner. This manner of hatching seems to be 
an excellent protective adaptation against egg parasites and other enemies. 
The mass is practically impervious to water. Thus from the time the 
egg is laid to the time when the larva hatches and enters the leaf to become 
a leaf miner, it is not once exposed to the direct dangers of enemies or of 
weather conditions. 
Once the larvae enter the leaf, they begin their work as typical leaf 
miners. The structure of the leaf of the cat-tail plant is rather peculiar. 
The fibro-vascular bundles are found mainly in longitudinal, I-like 
partitions. This produces a loose inner structure with many large air 
spaces (Plate XL, 11). The longitudinal partitions are again traversed 
by transverse partitions which also are composed of parenchyma. A 
leaf of Typha with the epidermis removed to show this inner structure 
appears in Plate XLV, 58. When the larvae have entered the leaf, they 
begin to mine, mostly downward, scraping off the chlorophyll from the 
upper and lower epidermis of the leaf. They eat out the transverse par- 
titions, leaving the longitudinal partitions and the fibro-vascular bundles 
undisturbed except when occasional larvae cut through to get in other 
channels. A few of the larvae may first mine upward toward the tip of 
the leaf, but soon they all proceed downward, moving abreast along the 
