254 MR. F. BALFOUR-BROWNE ON THE [ Mar. 2, 
and which finally crawls out of the water and dries itself in 
preparation for the final ecdysis. 
In this paper I propose to describe the details of the deve- 
lopment so far as I have been able to ascertain them ; and, while 
so doing, I shall incorporate a few casual observations on the 
anatomy which have been made in the course of the work and from 
watching the living creatures themselves. Although incomplete, 
these observations are, I believe, accurate, and may prove of 
some use to those interested in the comparative anatomy of the 
Insecta. 
I commenced studying the Dragonfly in 1903, at the Sutton 
Broad Laboratory; but it was not until July 1906 that I seriously 
undertook the investigation of the life-history. From the litera- 
ture on the Odonata I was able to obtain but little assistance. 
Packard (1866) published a paper on the development of the 
Dragonfly Diplax; but that paper deals for the most part with 
embryology, and the illustration of the newly-hatched larva— 
which is reproduced by Dr. Sharp, (1895, p. 419),—although truly 
representing the first stage of the true nymph, does not represent 
the creature as it comes out of the egg. Brandt, Dufour, Amans, 
Gilson, and various others who have worked at the Odonata have 
dealt with their anatomy and physiology, but not with their life- 
history; and W. J. Lucas (1900), in his book on the British 
Dragonflies, only refers in a general way to the life-history. He 
also makes the mistake of regarding the first stage of the true 
nymph of Sympetrum str iolatwm as the form lel emerges from 
the egg. 
It was necessary therefore to start de novo, and for this 
purpose I endeavoured to collect some eges from the dykes in 
the neighbourhood of the Laboratory. The females of all the 
Zygopteride, or thin-bodied dragonflies, like those of the 
AMschnide but unlike those of other Anisopterids such as Libel- 
lulide, Gomphidee, &c., are possessed of an ovipositor and lay 
their eggs in the tissues of floating aquatic plants. ‘They settle 
on a floating leaf of Hydrocharis, Potamogeton, Anacharis, &c., 
and dip the end of the abdomen into the water, often immersing 
the whole of it. According to some books, the females actually 
go under water at times when ovipositing; but I have never 
seen this. In the case of those plants with broad floating leaves, 
the apex of the abdomen is curved under the leaf so ‘that the 
ovipositor, which is on the ventral side of the 9th abdominal 
segment, is brought into contact with the lower surface. The 
ovipositor consists of two equal lobes placed side by side, each 
with a sharp point projecting backward. The two halves of the 
ovipositor work together and pierce a small hole in the leaf- 
tissue. They then separate slightly from each other, and 
between them a single elongated egg passes down and becomes 
wedged in the hole in the leaf. Only one egg is buried in each 
hole. Some discrimination is exercised as to the piercing of the 
plant-tissues, as the ovipositor moves about over the surface 
