Structure and Life-history of the Holly-fly. 281 
the female fly piercing the leaves with her ovipositor. 
She makes an incision with her pointed ovipositor, then 
steps backward and applies her tongue to the wound, as 
if she were extracting sap from the cells. Her movements 
at this time remind us of the way in which a fowl scratches 
the ground in search of a worm, and then steps back to 
examine the loosened soil. Egg-laying is a work of time 
with the holly-fly, for all the eggs are laid separately, and 
the female requires a regular supply of food. We have no 
reason to suppose that the male fly is able to draw sap 
from the cells of the leaf; it has to be content with what it 
finds on the leaf. Feeding-holes are made only in young 
and tender leaves; the ovipositor could not be made to 
penetrate an old leaf. Sometimes the fly fails to find the 
hole made by her own ovipositor, and then she makes 
another. While feeding the female is often visited by 
the male. When he is on the same leaf he seems to be 
guided to the spot by the working of the ovipositor; his 
movements become more alert as soon as he is aware of 
the presence of the female. Stealthily approaching while 
the female is absorbed in the act of feeding, he effects a 
secure embrace, from which he is not easily dislodged. 
The fertile female now proceeds to lay her eggs. She 
selects young leaves, but is now careful to pierce the 
under-side of the midrib, preferring a point near the base 
of the leaf. The piston-like ovipositor is repeatedly 
pressed up and down until the central vessels are reached. 
Then, by a contraction of the abdomen, an egg is passed 
into the hole. The fly tests the place with her tongue, 
and when satisfied goes off to another leaf. Thin sections 
through the place of oviposition show that a vertical shaft 
ascends from the hole; on reaching the vessels it makes 
a right-angled bend, and runs for a short distance along 
the vein; the egg is deposited in the horizontal part of 
the shaft. That the ovipositor is able to bend at a right 
angle can be made out by watching live flies. A captive 
female sometimes lays her egg, not in the midrib, but in 
the blade of the leaf, and this is, ina young leaf, sufficiently 
translucent to enable us to follow the action of the ovipositor. 
The wound made in the midrib is speedily closed by 
cork-cells. 
The egg (fig. 20) is of oval shape, and lies lengthwise in 
the midrib. One end is blunter than the other, and bears 
the micropyle; this end is turned towards the opening by 
