137 
on the Habits of the Purple Emperor. 
with yellow-spotted wings, and I never found them promiscuously 
coupled together ; but always a yellow-spotted male coupling 
with a yellow-spotted female, &c., which, by the bye, generally is 
in the evening ; this is the property of many butterflies (with the 
fore-feet imperfect) to couple in the evening. For though you 
see them playing together in the air all day long, they never 
couple till the approach of night and rest gives them leisure. 
They cohere great part of the night, and 1 have often found them 
coupled still in the morning. This hath made Mr. Rosel believe 
that this family of butterflies which fly in the day, couple only in 
flying over one another, as some sort of doves used to do. 
The way by which I used to get the eggs of these flies (which 
every one who has taken some pains in observing insects well 
knows to be very difficult) was to include them in a narrow dark 
vessel, with some leaves or branches of the plant I could probably 
guess to be the food of these caterpillars, without giving much air 
to the vessel, and, if the flies were too brisk, cutting their wings. 
In this way, I never failed to obtain eggs from any sort of flies, if 
there were any impregnated females among my prisoners. The 
purple emperor scatters its eggs, which are of a curious and ele- 
gant shape, up and down the leaves of the highest branches of the 
willow and oak, as I afterwards observed. They are always fixed 
with their flat bottom to the leaf, not that they acquire this figure 
by the flat surface they lie upon, for they are hardened before the 
fly discharges them, but as the eggs of many other flies and moths, 
being formed so in the womb, and fixed in this manner by the 
parent. The eggs of the purple emperor, while they are in the 
womb, are of a dark green colour, which they never change, being 
taken out unfecundated ; but when laid by an impregnated fe- 
male, they have a bright greenish yellow cast, and, in short, ac- 
quire a black or rather dark brown circle around the top, which 
is the place where afterwards the head of the caterpillar is formed 
and seen through the transparent shell. This is also the circle 
which the caterpillar, in forcing its passage, breaks, lifting up the 
top of the egg like a trap-door. 
The caterpillar, when it is first hatched, is of the same yellow 
colour with the egg, and in a very lean state in proportion to its 
dark brown head, which is roundish, and of the usual shape ob- 
servable in most caterpillars. Its first food is the empty whitish 
and transparent egg-shell, which some consume to the very 
bottom. But as soon as it is put upon a young leaf of the sallow 
willow, it climbs to the tip of it along the upper side of the rib, 
spinning all along the way, (though 1 could not imagine how so 
