1915} Life History Thelia Bimaculata 143 
individuals are very sluggish at this time and seldom move 
unless disturbed. The time taken in the field for the process 
is generally about twenty minutes, but one pair in the laboratory 
remained in cop for almost an hour. Mating continues through- 
out the summer, the largest number of cases being noted during 
the last week in August. The last date on which this process 
has been observed in the field was November 6th. 
In oviposition the female descends to the base of the tree, 
with the head pointing downward, and makes a narrow longi- 
tudinal slit about seven millimeters long in which the eggs are 
deposited. In very young stems the egg-slit sometimes pierces 
the wood but in most cases the ovipositor is deflected on striking 
the wood and slips to one side, the eggs being laid in the cam- 
bium between the bark and xylem. The slit is very narrow and 
hardly noticeable but the tips of the eggs may be seen protruding 
very slightly out of the bark when the process is completed 
(Fig. 3.) The eggs are about 2144 mm. long, white and club- 
shaped (Fig. 1). They are laid in a palmate formation (Fig. 2) 
recalling the egg-mass of Stictocephala inermis Fab.,* but much 
larger. The bases of the eggs are about 5 mm. apart and the 
apices compressed closely together. The number of eggs varies 
from three to six in a slit, the latter number being most common. 
The process occupies about forty minutes, after which the insect 
usually moves upward and slightly around the stem and repeats 
the process. One female has been known to make three such 
slits in succession, but as egg-laying is usually observed in the 
late afternoon it is difficult to keep field records on this score and 
the average number of egg-masses laid by one female at one 
time may be larger. Dissection shows the average number of 
eggs in the abdomen of the female to be twenty-eight. 
EMERGENCE AND DEVELOPMENT OF NYMPHS. 
The first numphs begin to appear in late May and early 
June. Field records made on May 30, 1911, June 1, 1912, 
June 2, 1913, and June 1, 1914, show that the early stages were 
collected on these dates. About two days before hatching, the 
tips of the eggs begin to crack and just before the nymphs 
emerge, break open at the top and usually split some distance 
down the side. 
*Agr. Exp. Sta. Tech. Bull. 17. Geneva, 1910. Pl. 2, Fig. 5. 
