DRAGONFLIES AND DAMSELFLIES IN PONDFISH CULTURE. 239 
LIBELLULA LUCTUOSA. 
The Egg.—The egg of this species is an almost perfect ellipse, o.57 mm. long and 0.30 mm. wide. 
The neck is conical, as wide at the base as it is high, with a distinct basal segment and a divided tip. 
There is also a short process at the posterior end of the egg; the yolk granules are comparatively large 
and distinct. Eggs laid on July 12 began to hatch July 22, and the hatching was entirely completed 
by July 30. Several lots of eggs from this species were hatched during the summer, and the period of 
incubation was practically the same for each lot. 
The Nymph.—The newly molted nymph is just 1 mm. in length, exclusive of the antenne; the 
head and abdomen are the same width, 0.38 mm.; the head is one-fifth wider than long; the hind 
legs are about the same length as the body, the first two pairs are proportionally shorter; the antenne 
are a little shorter than the head and rather stout. The head is a deep, sulphur yellow, the eyes are 
dark orange, with black spots, the digestive canal is light yellow, and the legs are banded with gray and 
white. 
As soon as the pronymph has molted and becomes a true nymph, the latter swims up to the surface 
of the water, accomplishing this locomotion by means of the legs, without any help from water ejection 
at the rectum. Having reached the surface the nymph is able to hold itself there by clinging to the 
surface film with its claws. It remains there for a long time almost motionless, so that, if the tumbler 
be examined at any time, the undersurface of the water film will be found covered with nymphs 2s 
Fics. 38 to 40.—Development of Libellula luctuosa: 38, egg; 39, mask of newly hatched nymph; 4o, newly hatched nymph. 
close together as they can stick. It often happens that one coming up from the bottom finds another 
already clinging to the film when it reaches the latter. It then fastens to the other nymph instead of 
to the film, and the combined weight of the two nymphs is more than the film can sustain, so that 
they sink slowly back to the bottom. Under natural conditions such a seeking of the surface brings 
the nymphs to the floating alge or other surface vegetation, which is evidently the location they seek 
for safety and food. It is also possible that the young nymph, like the teneral imago, needs the stronger 
sunlight for hardening its chitin integument and maturing its color pattern. 
The Mask.—Mentum twice as wide as long; distal margin two times the length of the proximal; 
four sete on the inner surface along either side near the lateral margin; three mental sete on eack 
side of the center in a straight line; a toothed prominence on the midline behind the distal margin. 
Lateral lobes one-half longer than wide; two marginal sete on the outer border near the base; two lami- 
nate sete on the blade of the lobe near the inner margin; raptorial seta just reaching the tip of the 
movable hook, the latter long and slender; distal border of lobe with five teeth near the outer corner, 
the second tooth the longest. 
