152 
J. BR0NT6 gatenby. 
to the insect as it walks over the Donacia egg mass. In 
collecting my material I found it most convenient to examine 
the rushes for Donacia egg-masses from a boat, and those 
upon which parasites were seen were removed from the 
water-plant and placed in a box. A most unfortunate circum- 
stance, unknown to me then, was the fact that the time 1 taken 
to walk to the laboratory with the material was just long 
enough to allow the newly-laid eggs to form polar bodies, 
segment, and enter upon the blastoderm stage. Except in 
the case of a small number of eggs laid in the laboratory, all 
my sections begin from the blastoderm stage onwards, and 
some important stages are missing. If the insect is taken 
into the laboratory and placed with an egg mass of Donacia, 
it is possible to watch oviposition taking place. The little 
parasite may be observed to walk somewhat rapidly over the 
eggs, continually tapping them with its geniculate antennae. 
When is satisfied with the egg it has chosen it stops, 
unsheaths its ovipositor, and moves its abdomen backwards 
and forwards with a sawing motion about eight times, until 
the chorion of the Donacia egg is pierced. When this 
happens the parasite may be seen to depress its abdomen, 
thrusting home the ovipositor. It pauses about five seconds 
while the egg passes down the evipositor into the Donacia 
egg, withdraws its ovipositor, and generally begins on the 
next egg in the row. Though the parasite does not seem 
to work systematically along the rows, in many cases all the 
eggs in a mass are parasitised, though more often a few are 
left untouched. 
In cases where all the eggs have been parasitised several 
parasites may have laid in one mass. It is quite common to 
observe two or three Trichogrammids on one Donacia egg- 
mass. In very rare cases there are two eggs laid in the 
same Donacia egg ; one so seldom finds this that it is 
probable that a parasite is able to tell whether one of its 
fellows has previously given attention to an egg. What 
1 Added to the fact that the fixative I used does not penetrate the 
chorion of the beetles’ eggs as quickly as desirable. 
